Well, it’s time for another viewfinder hack! I’ve been after one of these for a while, this is from an early 1980’s era Sony Trinicon camera, and instead of the tiny ½” round CRT display, these have a 1.5″ square CRT – a Matsushita 40CB4. Luckily I managed to score a pair of these from eBay for very little money. Update: The second camera’s viewfinder module turned out to have a dead flyback transformer, but at least I have a good spare CRT & the rest of the support components. More to come later on the teardown of the camera itself.
Mirror & Eyecup Assembly
The eyecup assembly with the magnifying lens & turning mirror is easy to remove, with clips & a single screw holding it onto the CRT holder sticking out of the side of the main casing.
Top Cover Removed
Removing some screws around the case allows the top cover to be removed, revealing the electronics. There’s certainly more in here than the later camera viewfinders, in this unit there are two boards slotted together with a board-to-board interconnect at the bottom. The CRT is at the top of the photo, hiding inside the plastic housing & deflection yoke assembly.
Bare PCBs & CRT
Here’s the CRT & one of the control boards removed from the case, having been stripped of the heatshrink tube that held the final anode lead in place. Just like on larger CRTs, this viewfinder has the final anode on a cavity connector fused into the bell, instead of being led out to a pin on the base. This is probably due to the much higher anode voltage of 5kV, a big jump from the 2kV on the ½” round tubes.
40CB4 CRT Label
Yup, it’s definitely the elusive 40CB4. Apparently these CRTs are still manufactured to this day for professional camera viewfinders, as the resolution of this small vacuum tube is still better than similarly sized modern tech such as LCDs or OLEDs. The phosphor used is type P4 – ZnS:Ag+(Zn,Cd)S:Ag, with an aluminized overcoat.
Bare 40CB4 CRT
After the base connector & deflection yoke are removed from the tube, the very long neck can be seen, this long glass neck apparently giving better focus & resolution than the stubbier tubes.
Electron Gun
The electron gun is the usual single unit as usually found in monochrome tubes.
Deflection Board
The bottom board in the assembly has all the control circuitry for the CRT, including the HA11244 deflection IC, composite sync separator & vertical deflection drive circuit. There are also circuits here to display a video waveform on the CRT, along with iris & white balance markers.
Horizontal Board
The other board has the horizontal drive circuitry, along with the video input amplifier. Despite the attempt to miniaturize the entire assembly, these are still well packed boards. Some of the resistors & diodes are bussed together in custom SIL hybrid modules to save PCB space. Like all the other CRT viewfinders, these units are meant for viewing via a mirror – the horizontal deflection coil connections need to be reversed to show a correct image without the mirror. The Red & Blue wires to the yoke need to be swapped here.
Flyback Transformer
The horizontal board on this unit also supports the flyback transformer, which is massive compared to the other viewfinder circuits. Biasing, focus & filament supplies for the CRT are also derived from this transformer, via auxiliary windings.
Boards Connected
The boards slot together in the centre to form the fully operational circuit.
Video Input
Out of the 3 plugs emerging from the cable feeding the viiewfinder, only this one is important, on the horizontal drive board. Black is ground, Brown +8.5v & red is composite video input. There’s also a resistor tied into the positive rail to the video input pin, which pulls it high to 8.5v – this is R1 right next to this connector. Desolder this 22K resistor to help protect anything feeding a signal into the unit, like a RPi, it’s not needed for normal operation.
Fallout!
As usual for a CRT post, the Fallout loading screen on the display. The picture quality isn’t as good as it should be, probably due to the noisy buck-converter I have rigged up for testing. If it doesn’t get better with a linear regulator, I’ll start replacing the 39 year old electrolytic capacitors. Current draw is 130mA at 7.5v. Schematics for this unit & the CRT datasheet are available below:
Time for another headphone amplifier! This is the Topping NX2, the upgrade from the NX1 I previously posted about. This one has a built in Burr Brown Audio DAC, along with the analogue audio input.
Audio I/O
The front of the unit has the audio connections, power switch & volume control wheel. Standard 3.5mm TRS jacks are used.
USB I/O
The other end holds a pair of USB Micro B connectors – one for charging the internal lithium cell, and the other providing a data interface for the internal DAC. A charge indicator LED is provided next to the charging port.
Main PCB
The PCB slides out of the casing, revealing a nice compact layout. The biggest item here is the lithium cell, providing all power to the unit.
Chipset
Audio amplification is handled by a Texas Instruments TP9260 Current-Feedback Class AB amplifier IC, with the USB Audio DAC being a Burr-Brown PCM2704. Nice Wima film capacitors are used on the input stage, although this amplifier suffers from a total lack of bass response – all low frequencies seem to get cut.
Well it was only a matter of time until we had a major failure of the onboard hydraulic system on board the boat, and this weekend proved to be that point in time.
Hose End
This is what remains of one of the main hoses to the propulsion motor, the fitting has been blown off the end of the hose! This occurred when I moved into reverse to stop the boat for oncoming traffic, and suddenly I lost all drive. The end result is a bilge filled with hydraulic oil, and zero power for manoeuvring.
The hose outer cover has been cut through by the fitting, like it had been sliced through with a knife, what remains of the inner liner & outer sheath is still in the fitting:
Fitting
Here’s the end of the offending fitting, with the remains of the hose. I suspect this termination wasn’t done correctly in the first place – either the swage was done too tight, cutting into the hose, or the fitting was never pushed all the way onto the hose before swaging, resulting in reduced strength.
Now comes the effort of cleaning out the roughly 40L of oil now in the bilges, refilling the oil tank & getting new hoses made up.
Here we have another piece of tech from Sterling Power – this is their Advanced Alternator Regulator, the Pro Reg D. Since I’m rejigging the alternator setup onboard, I figured I’d do a little teardown.
Cover Removed
Removing the top cover reveals the main PCB, which is slotted into the Aluminium heatsink extrusion. It’s a pretty well packed board, with both sides packed with tracks. There’s a small fan at the top of the unit, to keep the heatsink cool, but this has never worked for as long as this regulator has been in service.
Thermistor
Here would be the reason the fan has never operated – the thermistor which is supposed to monitor the temperature of the heatsink the MOSFETs are clamped to isn’t even in contact with it. Simply glopped with heatsink compound & stuck behind the SIL pad. This is a little sloppy to say the least, and should be in close thermal contact with the heatsink. I’ll have to adjust this mounting.
Field Control MOSFETs
Removing the heatsink shows the main field control FETs, both a P-Channel IRF4905 74A for positive field control, and a N-Channel IRF1010E 84A for negative field control. These are selected by moving the blade fuse between 3 spade terminals. Incedentally, Automotive-type blade fuses are not quick enough to protect semiconductors in the event of a serious fault, the likely result being an intact fuse & totally blown MOSFET. Nevermind.
Microcontroller
The unit is controlled by a Microchip PIC16F874, in a large package. There’s a couple of trimmers onboard for tweaking the calibration of the regulator, along with a dual DIP switch & a 12/24v link. Display is taken care of by a large row of indicator LEDs on a mezzanine board, there’s also a 4-pin Molex connector for a remote status display.
LED Board Mounting
The LED board is mounted to the main PCB with long pin headers, with no other support. Given the naturally vibrational nature of boats & their engines, having solder joints flapping about in the breeze isn’t a great plan, and fatigue is likely to set in here before long.
Loom Damage
Speaking of vibration, since the cable loom emerging from the aluminium case of the regulator is totally unprotected, the sharp edge of the extrusion has already begun chewing through the insulation! This has occurred after about 50 hours running time since the unit was installed. I’ll add a sleeve over the loom where it pops out of the corner to protect things better. Having the earthed aluminium casing munch it’s way through the insulation & short the entire loom out would not be a great result.
PCB Reverse
While I’ve got the board out of the casing, I’ve applied a heavy coat of PCB conformal coating to the back to help keep the moisture out, once everything is back together the top of the PCB will get the same treatment after masking off the parts that wouldn’t take kindly to a blasting with conformal coating.
Here’s another piece of tech, the electric air pump that’s available as an optional extra with Airbeam tents. I expected this to be a centrifugal blower, but instead it’s a large reciprocating air compressor – even if the construction quality is a little dubious for a device that costs over £70.
Pump Section
The internal parts of this pump are almost entirely made of plastic – not what I’d expect for an air compressor.
Valves
The valves are located on the end of the cylinder, the right hand on is the intake valve, the right is an pressure relief valve. The outlet valve is hidden inside the tube.
Drive Motor
The drive motor has the same model number as the overall pump, likely made specifically for this unit. This motor does have some cooling from a fan on the armature.
Crankshaft
After the cover has been removed from the pump unit, the main drive is visible. The driven gear is made of plastic, most likely nylon. The motor pinion is of brass. Ball bearings are used on the crank gear, but it appears that the big end bearing is a simple bushing on the steel pin.
Plastic Piston
The working cylinder & piston are also made of plastic, so I don’t hold up much hope of this unit wearing well, even though the plastic feels like Nylon 66, glass fibre reinforced. Plenty of grease has been applied to the moving parts at least, to help keep the friction down. The 20 minute limit on operating time most likely has a lot to do with the almost entirely plastic construction – the adiabatic heating of the air as it’s compressed will make short work of the relatively low melting point of the Nylon.
Electronics Section
The electronics are on a pair of PCBs tucked into the upper cover, one dealing with the pressure measurement, microcontroller & power control, and the other dealing with the display & buttons.
Power Control Board
The power control board has a 10A relay to switch power to the motor, along with a small microcontroller & pressure sensor, which is under the plastic adaptor on the PCB.
Display Board
The display is a standard 7-segment LCD, with a zebra strip connection to the PCB. Underneath hides the LCD controller itself. I’m not going to take this one off, as zebra strips don’t usually work properly once removed.
Microcontroller
The microcontroller is an Atmel ATTINY24A with 2K of onboard flash. The pressure sensor is on the right, although I haven’t been able to decode the laser-etched number on the top. Power is handled by a small linear regulator at the bottom edge of the board, with a couple of large electrolytics for filtering.
Power Control Board
Here’s an overall view of the power control board, with a better view of the pressure sensor & relay. This also gives a hint to the actual manufacturer of the pump – with the model number HB-630A. Since this unit is rated by their own admission at 13.5A, the 10A relay is likely to take a real beating over time. I measured 11A current draw at 7PSI output pressure.
Cheap car air compressors for inflating tyres are so cheap these days it’s almost impossible not to have to cut some corners. This one has failed catastrophically! These units are usually very poorly cooled, being housed in a closed plastic casing, with no airflow to speak of. The motor on this unit was fine, but the rest of the mechanical parts have taken a real beating.
Main Drive
I’ve removed the motor from the compressor head, leaving the main plastic drive gear exposed. The originally D keyed hole is now completely round, having been melted at some stage, the gear then just spins on the shaft without transmitting any drive.
Shaft Bearing
Here’s the crank main bearing, just a simple sleeve. There’s extreme wear present, about 2mm in total! This bearing has probably run dry of lubricant, then the steel shaft has just chewed through the relatively soft metal of the bearing, which is probably pot metal.
Bearing Wear
I’ve turned the shaft round here to show the large gap between the shaft & bearing bushing.
Main Bearing
This is what’s left of the bearing, complete with a coating of swarf.
Crankpin
The big end bearing of the connecting rod is also damaged – probably due to the play introduced by the rapidly disintegrating main bearing. At some stage the crankpin has worn through the rod enough for it to slip out entirely, leaving the piston stationary.
Piston Assembly
Wear in the side of the connecting rod shows that the spinning crank has been wearing it away for quite a while, eventually the rod probably fell into just the right spot to jam the crank, causing the failure of the main drive gear.
Here’s a nice little feature-packed USB power meter, the UM25C. This unit has USB-C along with the usual USB type A connectors, along with a bluetooth radio for remote monitoring of stats via a Windows or Android app. Construction is nice, it’s a stack of two PCBs, and polycarbonate cover plates, secured together with brass posts & screws.
Back Cover
The back cover has the legend for all the side connectors, along with the logo.
USB Micro Input
Down the sides are the user interface buttons, and here the Micro-B input connector. The 4-pin header is visible here that takes serial data down to the bluetooth section.
USB-C Connectors
The other side has the remaining pair of buttons, and the USB-C I/O. I don’t yet own anything USB-C based, but this is good future proofing.
LCD Display
Removing the top plastic cover plate reveals the small 1″ TFT LCD module. This will be hot-bar soldered underneath the screen. There’s an unused footprint next to the USB input connector, judging by the pin layout it’s probably for a I²C EEPROM.
Main Board Components
The underside of the top PCB has all the main components. The brains of the operation is a ST STM8S005C6T6 microcontroller. It’s at the basic end of the STM range, with a 16MHz clock, 32K flash, EEPROM, 10-bit ADC, SPI, UART & I²C. The main 0.010Ω current shunt is placed at the top left of the board in the negative rail. A couple of SOT-23 components in the centre of the board, I haven’t been able to identify properly, but I think they may be MOSFETs. The large electrolytic filter capacitor has a slot routed into the PCB to allow it to be laid flat. Providing the main power rail is a SOT-89 M5333B 3.3v LDO regulator.
Bluetooth Radio
The bottom board contains the bluetooth radio module, this is a BK3231 Bluetooth HID SoC. The only profile advertised by this unit is a serial port. There’s a local 3.3v LDO regulator & support components, along with an indicator LED.
Here’s a cheapo 532nm green laser pointer courtesy of eBay, this one rolled in at £7, with 18650 cell & charger included. Advertised at 1mW, I was immediately suspicious of the output power since this unit quite easily causes skin burns.
Laser Warning Label
The warning label rates this laser at Class III, with an output power of <1000mW. Massively higher than the 1mW advertised. The end cap is split into two parts that are threaded – the first one is a starfield effect diffraction grating, while the second one moves the final optic to focus the beam.
Starfield Diffraction Grating
The starfield gratings are mounted inside a brass ferrule, which can be rotated to alter the effect without unscrewing from the main body.
Optics Removed
Removing the output optic barrel reveals the end of the DPSS laser module, which appears to be well glued in. The aluminium cylinder doesn’t appear to have any other purpose other than to protect the laser output end.
KTP Crystal & Lens
Unscrewing the cylinder reveals the glued holder containing the KTP crystal, and the first output optic. The beam from this alone is very divergent, expanding to ~100mm over a meter or so. The beam right at the optic though is highly focussed & is quite capable of cutting through black electrician’s tape.
There’s also no IR filter anywhere in the optical path – so there is going to be a high power 808nm/1064nm component to the beam since these wavelengths are used in the DPSS process. Since these components are totally invisible, the risk for eye damage is higher due to lack of a blink reflex.
Power Reading
On to the power reading… 351mW of output at 532nm. So quite a bit more than the advertised spec then, but lower than the warning label states. This puts this unit into Class IIIB.
Cell Capacity
From a full charge, down to 2.8v, the “4000mAh” cell provided with this unit managed a pitiful 1128mAh. I knew from the second I got this cell that it would be a fake, since decent 18650 lithium-ion cells cost about the same as this whole package.
Fake Cell
This cell claims a 4000mAh capacity, and built in protection circuit. Let’s dig under the sleeve…
Nope. No protection circuit here. It’s easy to tell anyway – protected cells are longer, and usually the strap buggering off to the other end of the cell is visible through the sleeve. There is a dual-layer sleeve though, of clear PVC under the BRC branded one. No other markings on the cell at all, and it’s suspiciously light in weight.
Here’s the CRT & it’s drive board removed from the main chassis. Nicely modular this unit, all the individual modules (radio, tape, TV), are separate. This is effectively a TV itself, all the tuner & IF section are onboard, unlike in other vintage units I’ve modified, where the tuner & IF has been on a separate board. There’s a 3-pin header bottom centre for the tuning potentiometer, and external antenna input jack. The internal coax for the built in antenna has been desoldered from the board here. here a the usual controls on the back for adjusting brightness, contrast & V Hold, all the other adjustments are trimmers on the PCB.
Unfortunately after 30+ years of storage, this didn’t work on first power up, neither of the oscillators for vertical or horizontal deflection would lock onto the incoming signal, but a couple of hours running seemed to improve things greatly. The numerous electrolytic capacitors in this unit were probably in need of some reforming after all this time, although out of all of them, only 21 are anything to do with the CRT itself.
Anode Cap
Here’s the anode side of the unit, with the small flyback transformer. The rubber anode cap has become very hard with age, so I’ll replace this with a decent silicone one from another dead TV. The Horizontal Output Transistor (a 2SC2233 NPN type) & linearity coil are visible at the bottom right corner of the board. Unfortunately, the disgusting yellow glue has been used to secure some of the wiring & large electrolytics, this stuff tends to turn brown with age & become conductive, so it has to be removed. Doing this is a bit of a pain though. It’s still a little bit flexible in places, and rock hard in others. Soaking in acetone softens it up a little & makes it easier to detach from the components.
Neck PCB
There’s little on the neck board apart from a few resistors, forming the limiting components for the video signal, and the focus divider of 1MΩ & 470KΩ feeding G3. No adjustable focus on this unit. There’s also a spark gap between the cathode line & ground, to limit the filament to cathode voltage. The flyback transformer is nestled into the heatsink used by the horizontal output transistor & a voltage regulator transistor.
Tube Details
The CRT is a Samsung Electron Devices 4ADC4, with a really wide deflection angle. It’s a fair bit shorter than the Chinese CRT I have which is just a little larger, with a neck tube very thin indeed for the overall tube size.
Unusually, while the filament voltage is derived from the flyback transformer as usual, it’s rectified into DC in this unit, passing through a 1Ω resistor before the filament connection. I measured 5.3v here. The glow from the filament is barely visible even in the dark.
Electron Gun 1
The electron gun is the usual for a monochrome tube, with 7 pins on the seal end.
Electron Gun 2
The electrodes here from left are Final Anode, G3 (Focus Grid), Accelerating Anode, G2 (Screen Grid), G1 (Control Grid). The cathode & filament are hidden inside G1. In operation there’s about 250v on G2, and about 80v on G3.
Chipset
The chipset used here is all NEC, starting with a µPC1366C Video IF Processor, which receives the IF signal from the tuner module to the left. This IC outputs the standard composite signal, and a modulated sound signal.
This then splits off to a µPC1382C Sound IF Processor & Attenuator IC, which feeds the resulting sound through the two pin header at the right bottom edge of the board to the audio amplifier in the chassis.
The composite video signal is fed through a discrete video amplifier with a single 2SC2229 transistor before going to the CRT cathode.
The remaining IC is a µPC1379C Sync Signal Processor, containing the sync separator, this is generating the required waveforms to drive the CRT deflection systems from another tap off the composite video line.
From this chip I can assume the unit was built around 1986, since this is the only date code on any of the semiconductors. Besides these 3 ICs, the rest of the circuit is all discrete components, which are well-crammed into the small board space.
There are 5 trimmer potentiometers on the board here, I’ve managed to work out the functions of nearly all of them:
SVR1: IF Gain Adjust
SVR2: H. Hold
SVR3: V. Size
SVR4: B+ Voltage Adjust
SVR5: Tuner Frequency Alignment? It’s in series with the tuning potentiometer in the chassis.
PCB Bottom
The PCB bottom shows the curved track layout typical of a hand taped out board. The soldermask is starting to flake off in places due to age, and there a couple of bodge wires completing a few ground traces. Respinning a board in those days was an expensive deal! Surprisingly, after all this time I’ve found no significant drift in the fixed resistors, but the carbon track potentiometers are drifiting significantly – 10KΩ pots are measuring as low as 8KΩ out of circuit. These will have to be replaced with modern versions, since there are a couple in timing-sensitive places, like the vertical & horizontal oscillator circuits.
Anode Cap Replaced
Here the anode cap has been replaced with a better silicone one from another TV. This should help keep the 6kV on the CRT from making an escape. This was an easy fix – pulling the contact fork out of the cap with it’s HT lead, desoldering the fork & refitting with the new cap in place.
Here I’ve replaced the important trimmers with new ones. Should help stabilize things a little.
Composite Injection Mod
Injecting a video signal is as easy as the other units. Pin 3 of the µPC1366C Video IF Processor is it’s output, so the track to Pin 3 is cut and a coax is soldered into place to feed in an external signal.
CRT In Operation
After hooking up a Raspberry Pi, we have display! Not bad after having stood idle for 30+ years.
Datasheets for the important ICs are available below:
[download id=”5690″]
[download id=”5693″]
[download id=”5696″]
Here’s a destructive teardown of an automotive in-tank turbine fuel pump, used on modern Petrol cars. These units sit in the tank fully immersed in the fuel, which also circulates through the motor inside for cooling. These pumps aren’t serviceable – they’re crimped shut on both ends. Luckily the steel shell is thin, so attacking the crimp joint with a pair of mole grips & a screwdriver allowed me inside.
End Bell
The input endbell of the pump has the fuel inlet ports, the channels are visible machined into the casting. There’s a pair of channels for two pump outputs – the main fuel rail to the engine, and an auxiliary fuel output to power a venturi pump. The fuel pump unit sits inside a swirl pot, which holds about a pint of fuel. These are used to ensure the pump doesn’t run dry & starve the engine when the tank level is low & the car is being driven hard. The venturi pump draws fuel from the main tank into the swirl pot. A steel ball is pressed in to the end bell to provide a thrust bearing for the motor armature.
Turbine Impeller
The core of the pump is this impeller, which is similar to a side-channel blower. From what I’ve been able to find these units supply pressures up to about 70PSI for the injector rail. The outside ring is the main fuel pump, while the smaller inner one provides the pressure to run the venturi pump.
Pump Housing
The other side of the machined pump housing has the main output channel, with the fuel outlet port at the bottom. The motor shaft is supported in what looks like a carbon bearing.
Midsection
Removing the pump intermediate section with the bearing reveals quite a bit of fungus – it’s probably been happy sat in here digesting what remains of the fuel.
Armature Exposed
Some peeling with mole grips allows the motor to come apart entirely. The drive end of the armature is visible here.
Motor Can
The outer shell of the motor holds yet more fungus, along with some rust & the pair of ceramic permanent magnets.
Brushes
The other end of the pump has the brush assembly, and the fuel outlet check valve to the right. The bearing at this end is just the plastic end cap, since there are much lower forces at this end of the motor. The fuel itself provides the lubrication required.
Potted Armature
With the armature pulled out of the housing, it’s clear that there’s been quite a bit of water in here as well, with the laminations rusting away. This armature is fully potted in plastic, with none of the copper windings visible.
Carbon Commutator
The commutator in these motors is definitely a strange one – it’s axial rather than radial in construction, and the segments are made of carbon like the brushes. No doubt this is to stop the sparking that usually occurs with brushed motors – preventing ignition of fuel vapour in the pump when air manages to get in as well, such as in an empty tank.
Here’s one of the old modems from my spares bin, a Vodafone Mobile WiFi R207. This is just a rebranded Huawei E5330. This unit includes a 3G modem, and a WiFi chipset, running firmware that makes this a mini-router, with NAT.
Specs
The back has the batter compartment & the SIM slot, with a large label showing all the important details.
Cover Removed
A couple of small Torx screws later & the shell splits in half. All the electronics are covered by shields here, but luckily they are the clip-on type, and aren’t soldered direct to the PCB.
Chipset
Once the shield has been removed, the main chipset is visible underneath. There’s a large Spansion MS01G200BHI00 1GBit flash, which is holding the firmware. Next to that is the Hi6758M baseband processor. This has all the hardware required to implement a 3G modem. Just to the right is a Hi6521 power management IC, which is dealing with all the power supplies needed by the CPU.
The RF section is above the baseband processor, some of which is hiding under the bits of the shield that aren’t removable.
SIM Socket
There’s a socket onboard for a standard Mini-SIM, just to the left of that is a Hi6561 4-phase buck converter. I would imagine this is providing the power supplies for the RF section & amplifier.
Unpopulated Parts
Not sure what this section is for, all the parts are unpopulated. Maybe a bluetooth option?
PCB Reverse
The other side of the PCB is pretty sparse, holding just the indicator LEDS, button & the WiFi Chipset.
Realtek WiFi Chipset
The chipset here is a Realtek part, but it’s number is hidden by some of the shield. The antenna connection is routed to the edge of the board, where a spring terminal on the plastic case mounted antenna makes contact.
Now the trolley is pretty much built, some burn-in testing is currently underway before it’s first trial-by-fire at Download Festival. There are a couple of minor issues that have needed fixing, since everything is enclosed in a pretty tight box.
Lagging
The Eberspacher was the first point that needed sorting – the radiant heat from the hot air ducting was pretty much cooking everything around it – the inverter’s heatsink got to temperatures in the 50°C range. I pullsed some ceramic fibre lagging from a decomissioned domestic oven, and entirely lagged the hot end of the heater, securing everything with cable ties. Good stuff this, the inside of the box now hardly even warms up, nearly all of the heat going out through the vent where it’s needed.
The intake was also an issue, since these heaters adjust their power levels based on inlet air temperature, pulling the air from inside the box was infeasible, since within a few minutes the heater thinks the ambient temperature has reached 30°C, resulting in a shutdown. Another vent has been fitted in the back panel, drawing cool air into the heater’s fan.
Finally, meet FrankenCompressor:
FrankenCompressor
I didn’t have the time to order a proper 12v compressor in time for this year, so after some rummaging around in the parts bin & came up with a couple of 12v car tyre inflator type compressor units. These are pretty crap for proper air compressor use, but they should survive just long enough to get me through this year. They’re mounted to a wooden board, with a large 120mm high-speed server fan mounted on the end, blowing a huge amount of air over the cylinders to help cool them down. Output is channelled through a couple of modified 6mm push-fit pneumatic fittings epoxied onto the factory hose barbs. Copper tubing helps cool the compressed air before the transition to poly tube.
Since I do festivals every year, along with a couple of other camping trips if the weather is good enough, I’ve been taking equipment with me for years in flight cases to make things more comfortable. Things like a large battery to power lights & device charging, an old Eberspacher diesel heater for the times when the weather isn’t great, and an inverter to run the pumps built into airbeds.
Red Diesel / Heating Oil is my fuel of choice for camping purposes, as it’s about the safest fuel around, unlike Butane/LPG it is not explosive, will not burn very readily unless it’s atomized properly & it’s very cheap. Paraffin is an alternative fuel, but it’s expensive in the UK, at about £12 per 5L.
The Hexamine-based tablet fuels the UK festivals promote is nasty stuff, and the resulting combustion products are nastier still. (Things like Hydrogen Cyanide, Formaldehyde, Ammonia, NOX). They also leave a sticky black grok on every cooking pot that’s damn near impossible to remove. Meths / Trangia stoves are perfectly usable, but the flame is totally invisible, and the flammability of alcohol has always made me nervous when you’ve got a small pot of the stuff boiling while it’s in operation in the middle of a campsite filled with sloshed festival goers. A single well-placed kick could start a massive fire.
Previous System
Over the years the gear has evolved and grown in size, so I decided building everything into one unit on wheels would be the best way forward. I’ve been working on this for some time, so it’s time to get some of the details on the blog! Above you can see the system used for last year’s camping, the heater is separate, with a 25L drum of heating oil, the battery is underneath the flight case containing all the power components, and it’s currently charging All The Things.
Overview
Above is the new unit almost finished, the bottom frame is a standard eBay-grade 4-wheel trolley with a few modifications of my own, with a new top box built from 12mm hardwood marine plywood. This top is secured in place with coach bolts through the 25mm angle iron of the trolley base. The essential carbon monoxide detector is fitted at the corner.
Internal View
The inside gets a bit busy with everything crammed in. The large Yuasa 200Ah lead-acid battery is at the far end, with it’s isolation switch. Right in the middle is the Eberspacher heater with it’s hot air ducting. I’ve fitted my usual 12/24v dual voltage system here, with the 24v rail generated from a large 1200W DC-DC converter.
Heater Vent
The hot air duct for the heater is fed out through a standard vent in the front. Very handy for drying out after a wet day.
Main Bus Bars & Solar Controller
Here’s a closeup of the distribution bus bars, with both negative rails tied together in the centre to keep the positives as far away from each other as possible, to reduce the possibility of a short circuit between the two when working on the wiring. The EpEver Tracer 4210A MPPT Solar Charge Controller is on the left, tucked into the corner. This controller implements the main circuit protection for the battery, having a 40A limit. Individual circuits are separately fused where required. Solar input on this unit is going to be initially provided by a pair of 100W flexible panels in series for a 48v solar bus, the flexible panels are essential here as most of the festivals I attend do not allow glass of any kind onsite, not to mention the weight of rigid panels is a pain.
DC Output Sockets
I’ve stuck with the 3-pin XLR plugs for power in this design, giving both the 12v rail, 24v rail & ground.
Inverter Outputs
Tucked under the DC outputs are a pair of panel sockets for the 600W inverter. This cheapo Maplin unit is only usually used to pump up air beds, so I’m not expecting anyone to pull anything near max output, but a warning label always helps.
Power Socket Wiring
Behind the front panel is the hardwiring for the power sockets. The DC jacks are connected together using 2mm solid copper wire, bent into bus bars.The mains wiring underneath is a simple radial circuit straight from the inverter. The large cylinder on the left is a hydraulic pump from a BMW Z3, which runs a hydraulic cylinder for lifting the lid of the top box, used simply because I had one in the box of junk.
Fuel Pump
External fuelling is dealt with by a small gear pump, this is used to fuel up the Optimus Stove & Petromax Lantern. This is in fact a car windscreen wash pump, but it has coped well with pumping hydrocarbons, it currently has a small leak on the hose connections, but the seals are still entirely intact.
Remote Relays
There’s a small remote relay module here, for switching the DC output for lighting & the heater from afar. Very useful when it’s dark, since there’s no need to fumble around looking for a light switch. A car-style fob on my keyring instead.
Heater Timer
Since the Eberspacher 701 controller I have is an ex-BT version, it’s very limited in it’s on time, a separate timeswitch is fitted to control the heater automatically. Being able to return to a nice warm tent is always a bonus.
Just to the left can be seen the top ball joint for the hydraulic cylinder that lifts the top of the box.
Battery Charger
The final large component is the battery charger. This unit will maintain the battery when the trolley isn’t being used.
Router Motherboard
On the left side is the old Atom motherbaord used to provide a 4G router system. This unit gets it’s internet feed from a UMTS dongle & provides a local WiFi network for high speed connectivity. The bottom of the hydraulic cylinder is visible in the bottom right corner.
Fuel Tank Completed
Since the Eberspacher obviously needs fuel, a tank was required. In previous years I’ve used jerry cans for this purpose, but this trolley is supposed to have everything onboard, for less setup time. The tank is constructed from 3mm steel plate, MIG welded together at the seams to create a ~40L capacity. The filler neck is an eBay purchase in Stainless Steel. No photos of the tank being welded together, as I was aiming to beat sunset & it’s very difficult to operate a camera with welding gauntlets on 😉
The tank is the same width as the trolley frame, so some modification was required, having the wheels welded directly to the sides of the tank. This makes the track wider at the rear, increasing stability.
Fuel Dip Tubes
A quick view inside the tank through the level sender port shows the copper dip tubes for fuel supply to the heater, and an external fuel hose for my other fuel-powered camping gear. These tubes stop about 10mm from the bottom of the tank to stop any moisture or dirt from being drawn into the pumps.
Fuel Feeds & Level Sender Port
The top of the tank is drilled for the fuel fittings & the level sender and has already been painted here. The 1mm base plate has yet to be painted.
Level Sender Installed
Touching up the paint & fitting the sender is the last job for this part. The mesh bottom of the trolley has been replaced by a 1mm steel sheet to support the other parts, mainly the heater. Fuel lines are run in polyurethane tubing to the fuel pumps.
All the instruments & controls are on a single panel, with the Eberspacher thermostat, external fuelling port & pump switch, inverter control, the solar controller monitor panel, cover buttons, router controls, compressed air & fuel gauges.
Panel Wiring
As is usual behind instrument panels, there’s a rat’s nest of wiring. There’s still the pressure gauge to connect up for the compressed air system, and the nut on one of the router buttons is such a tight fit I’ve not managed to get it into place yet.
Eberspacher Fuel Pump
The support components for the Eberspacher heater are mounted underneath the baseplate, with the fuel dosing pump secured to a rail with a pair of cable ties, and some foam tape around to isolate the constant clicking noise these pumps create in operation. The large black cylinder is the combustion air intake silencer, with the stainless steel exhaust pipe to the left of that. Silencing these heaters is essential – they sound like a jet engine without anything to deaden the noise. Most of this is generated from the side-channel blower used in the burner.
Eberspacher Exhaust
Bolted to the underside are a pair of exhaust silencers, one is an Eberspacher brand, the other is Webasto, since the latter type are better at reducing the exhaust noise. Connections are sealed with commerical exhaust assembly paste, the usual clamps supplied do not do a good enough job of stopping exhaust leaks.
Next update to come when I get the parts in for the air compressor system.
Since I seem to be the local go-to for any dead electrical equipment, this brand-new Silverline polisher has landed on my desk. Purchased cheap from an auction this was dead on arrival. Checking the fuse revealed nothing suspect, so a quick teardown to find the fault was required.
Above is a photo of the commutator with the brush holder removed, and the source of the issue. The connection onto the field winding of the universal motor has been left unsecured, as a result it’s managed to move into contact with the commutator.
This has done a pretty good job of chewing it’s way through the wire entirely. There is some minor damage to the commutator segments, but it’s still smooth, and shouldn’t damage the brushes.
Chewed Wire
A quick pull on what’s left of the wire reveals the extent of the problem. It’s entirely burned through! Unfortunately the stator assembly with the field windings is pressed into the plastic housing, so it’s not removable. An in-place solder joint was required to the very short remains of the wire inside the housing. Once this was done the polisher sprang to life immediately, with no other damage.
This unit probably ended up at an auction as a factory reject, or a customer return to a retail outlet. If the latter, I would seriously question the quality control procedures of Silverline tools. 😉
The Sterling charger we’ve had on board nb Tanya Louise since Feb 2014 has bitten the dust, with 31220 hours on it’s internal clock. Since we’re a liveaboard boat, this charger has had a lot of use while we’re on the mooring during winter, when the solar bank isn’t outputting it’s full rate. First, a bit of a teardown to explore the unit, then onto the repair:
Active PFC Section
There’s the usual mains input filtering on the left, with the bridge rectifier on it’s heatsink.
Underneath the centre massive heatsinks is the main transformer (not visible here) & active PFC circuit. The device peeking out from underneath is the huge inductor needed for PFC. It’s associated switching MOSFET is to the right.
Logic PSU Section
On the other side of the PFC section is the main DC rail filter electrolytic, a 450v 150µF part. Here some evidence of long-term heating can be seen in the adhesive around the base, it’s nearly completely turned black! It’s not a decent brand either, a Chinese CapXon.
The PCB fuse just behind it is in the DC feed to the main switching supply, so the input fuse only protects the filter & Active PFC circuitry. Luckily this fuse didn’t blow during the failure, telling me the fault was earlier in the power chain.
The logic circuits are powered by an independent switching supply in the centre, providing a +5v rail to the microcontroller. The fan header & control components are not populated in this 10A model, but I may end up retrofitting a fan anyway as this unit has always run a little too warm. The entire board is heavily conformal coated on both sides, to help with water resistance associated with being in a marine environment. This has worked well, as there isn’t a single trace of moisture anywhere, only dust from years of use.
There is some thermal protection for the main SMPS switching MOSFETS with the Klixon thermal fuse clipped to the heatsink.
DC Output Section
The DC output rectifiers are on the large heatsink in the centre, with a small bodge board fitted. Due to the heavy conformal coating on the board I can’t get the ID from this small 8-pin IC, but from the fact that the output rectifiers are in fact IRF1010E MOSFETS, rated at 84A a piece, this is an synchronous rectifier controller.
Oddly, the output filter electrolytics are a mix of Nichicon (nice), and CapXon (shite). A bit of penny pinching here, which if a little naff since these chargers are anything but cheap. (£244.80 at the time of writing).
Hiding just behind the electrolytics is a large choke, and a reverse-polarity protection diode, which is wired crowbar-style. Reversing the polarity here will blow the 15A DC bus fuse instantly, and may destroy this diode if it doesn’t blow quick enough.
DC Outputs
Right on the output end are a pair of large Ixys DSSK38 TO220 Dual 20A dual Schottky diodes, isolating the two outputs from each other, a nice margin on these for a 10A charger, since the diodes are paralleled each channel is capable of 40A. This prevents one bank discharging into another & allows the charger logic to monitor the voltages individually. The only issue here is the 400mV drop of these diodes introduce a little bit of inefficiency. To increase current capacity of the PCB, the aluminium heatsink is being used as the main positive busbar. From the sizing of the power components here, I would think that the same PCB & component load is used for all the chargers up to 40A, since both the PFC inductor & main power transformer are massive for a 10A output. There are unpopulated output components on this low-end model, to reduce the cost since they aren’t needed.
Front Panel Control Connections
A trio of headers connect all the control & sense signals to the front panel PCB, which contains all the control logic. This unit is sensing all output voltages, output current & PSU rail voltages.
Front Panel LEDs
The front panel is stuffed with LEDs & 7-segment displays to show the current mode, charging voltage & current. There’s 2 tactile switches for adjustments.
Front Panel Reverse
The reverse of the board has the main microcontroller – again identifying this is impossible due to the heavy conformal coat. The LEDs are being driven through a 74HC245D CMOS Octal Bus Transceiver.
Now on to the repair! I’m not particularly impressed with only getting 4 years from this unit, they are very expensive as already mentioned, so I would expect a longer lifespan. The input fuse had blown in this case, leaving me with a totally dead charger. A quick multimeter test on the input stage of the unit showed a dead short – the main AC input bridge rectifier has gone short circuit.
Bridge Rectifier Removed
Here the defective bridge has been desoldered from the board. It’s a KBU1008 10A 800v part. Once this was removed I confirmed there was no longer an input short, on either the AC side or the DC output side to the PFC circuit.
Testing The Rectifier
Time to stick the desoldered bridge on the milliohm meter & see how badly it has failed.
Yep, Definitely Shorted
I’d say 31mΩ would qualify as a short. It’s no wonder the 4A input fuse blew instantly. There is no sign of excessive heat around the rectifier, so I’m not sure why this would have failed, it’s certainly over-rated for the 10A charger.
Testing Without Rectifier
Now the defective diode bridge has been removed from the circuit, it’s time to apply some controlled power to see if anything else has failed. For this I used a module from one of my previous teardowns – the inverter from a portable TV.
Test Inverter
This neat little unit outputs 330v DC at a few dozen watts, plenty enough to power up the charger with a small load for testing purposes. The charger does pull the voltage of this converter down significantly, to about 100v, but it still provides just enough to get things going.
It’s Alive!
After applying some direct DC power to the input, it’s ALIVE! Certainly makes a change from the usual SMPS failures I come across, where a single component causes a chain reaction that writes off everything.
Replacement Rectifier
Unfortunately I couldn’t find the exact same rectifier to replace the shorted one, so I had to go for the KBU1010, which is rated for 1000v instead of 800v, but the Vf rating (Forward Voltage), is the same, so it won’t dissipate any more power.
Soldered In
Here’s the new rectifier soldered into place on the PCB & bolted to it’s heatsink, with some decent thermal compound in between.
Input Board
Here is the factory fuse, a soldered in device. I’ll be replacing this with standard clips for 20x5mm fuses to make replacement in the future easier, the required hole pattern in the PCB is already present. Most of the mains input filtering is also on this little daughterboard.
Fuse Replaced
Now the fuse has been replaced with a standard one, which is much more easily replaceable. This fuse shouldn’t blow however, unless another fault develops.
Full Load Test
Now everything is back together, a full load test charging a 200Ah 12v battery for a few hours will tell me if the fix is good. This charger won’t be going back into service onboard the boat, it’s being replaced anyway with a new 50A charger, to better suit the larger loads we have now. It won’t be a Sterling though, as they are far too expensive. I’ll report back if anything fails!
Here’s another random bit of RF tech, I’m told this is a wireless energy management sensor, however I wasn’t able to find anything similar on the interwebs. It’s powered by a standard 9v PP3 battery.
Microcontroller
System control is handled by this Microchip PIC18F2520 Enhanced Flash microcontroller, this has an onboard 10-bit ADC & nanoWatt technology according to their datasheet. There’s a 4MHz crystal providing the clock, with a small SOT-23 voltage regulator in the bottom corner. There’s a screw terminal header & a plug header, but I’ve no idea what these would be used for. Maybe connecting an external voltage/current sensor & a programming header? The tactile button I imagine is for pairing the unit with it’s controller.
PCB Bottom
The bottom of the PCB is almost entirely taken up by a Radiocrafts RC1240 433MHz RF transceiver. Underneath there’s a large 10kΩ resistor, maybe a current transformer load resistor, and a TCLT1600 optocoupler. Just from the opto it’s clear this unit is intended to interface in some way to the mains grid. The antenna is connected at top right, in a footprint for a SMA connector, but this isn’t fitted.
These photos were sent over to me by a friend, an interesting piece of tech that’s used in the retail industry. This is a BluVision BLE Beacon, which as far as I can tell is used to provide some automated customer assistance. From their website it seems they can also be used for high-price asset protection & tracking. These units don’t appear to be serviceable, being completely sealed & only having a primary cell. I’m not sure what they cost but it seems to be an expensive way to contact clients with adverts etc.
Component Side
There’s not much populated on this PCB, the main component here is the CC2640 SimpleLink ultra-low-power wireless microcontroller for Bluetooth Low Energy. It’s a fairly powerful CPU, with an ARM Cortex M3 core, 129KB of flash & up to 48MHz clock speed. There’s a couple of crystals, one of which is most likely a 32,768kHz low-power sleep watch crystal, while the other will be the full clock frequency used while it’s operating. Unfortunately I can’t make the markings out from the photos. There doesn’t appear to be any significant power supply components, so this must be running direct from the battery underneath.
2.2Ah 3.6v Lithium Cell
The other side of the PCB has a single primary lithium cell, rated at 3.6v, 2.2Ah. The factory spec sheet specifies a 2.2 year life at 0dBm TX Power, Running 24/7, 100ms advertisement rate.
Being in technology for a long time, I have seen my fair share of disk failures. However I have never seen a single instance where SMART has issued a sufficient warning to backup any data on a failing disk. The following is an example of this in action.
Toshiba MQ01ABD050
Here is a 2.5″ Toshiba MQ01ABD050 500GB disk drive. This unit was made in 2014, but has a very low hour count of ~8 months, with only ~5 months of the heads being loaded onto the platters, since it has been used to store offline files. This disk was working perfectly the last time it was plugged in a few weeks ago, but today within seconds of starting to transfer data, it began slowing down, then stopped entirely. A quick look at the SMART stats showed over 4000 reallocated sectors, so a full scan was initiated.
SMART Test Failure
After the couple of hours an extended test takes, the firmware managed to find a total of 16,376 bad sectors, of which 10K+ were still pending reallocation. Just after the test finished, the disk began making the usual clicking sound of the head actuator losing lock on the servo tracks. Yet SMART was still insisting that the disk was OK! In total about 3 hours between first power up & the disk failing entirely. This is possibly the most sudden failure of a disk I’ve seen so far, but SMART didn’t even twig from the huge number of sector reallocations that something was amiss. I don’t believe the platters are at fault here, it’s most likely to be either a head fault or preamp failure, as I don’t think platters can catastrophically fail this quickly. I expected SMART to at least flag that the drive was in a bad state once it’s self-test completed, but nope.
Internals
After pulling the lid on this disk, to see if there’s any evidence of a head crashing into a platter, there’s nothing – at least on a macroscopic scale, the single platter is pristine. I’ve seen disks crash to the point where the coating has been scrubbed from the platters so thoroughly that they’ve been returned to the glass discs they started off as, with the enclosure packed full of fine black powder that used to be data layer, but there’s no indication of mechanical failure here. Electronic failure is looking very likely.
Clearly, relying on SMART to alert when a disk is about to take a dive is an unwise idea, replacing drives after a set period is much better insurance if they are used for critical applications. Of course, current backups is always a good idea, no matter the age of drive.
Ah the curse of the Chinese Electronics strikes again. These large DC-DC boost converters have become very common on the likes of AliExpress & eBay, and this time my order has arrived DOA… On applying power, the output LED lights up dimly, and no matter how I twiddle the adjustment pots, the output never rises above the input voltage.
Boost Converter Topology
From the usual topology above, we can assume that the switching converter isn’t working, so the input voltage is just being directly fed through to the output. The switching IC on these converters is a TL494,
Control Circuitry
The switching IC on these converters is a TL494,with it’s surrounding support components, including a LM358 dual Op-Amp. Power for this lot is supplied from the input via a small DC-DC converter controlled by an XL Semi XL7001 Buck Converter IC. Some testing revealed that power was getting to the XL7001, but the output to the switching controller was at zero volts.
Inductor
The 100µH inductor for this buck converter is hidden behind the output electrolytic, and a quick prod with a multimeter revealed this inductor to be open circuit. That would certainly explain the no-output situation. Luckily I had an old converter that was burned out. (Don’t try to pull anything near their manufacturer “rating” from these units – it’s utter lies, more about this below).
Donor Converter
The good inductor from this donor unit has been desoldered here, it’s supposed to be L2. This one had a heatsink siliconed to the top of the TL494 PWM IC, presumably for cooling, so this was peeled off to give some access.
After this inductor was grafted into place on the dead converter, everything sprang to life as normal. I fail to see how this issue wouldn’t have been caught during manufacture, but they’re probably not even testing them before shipping to the distributor.
The sensational ratings are also utter crap – they quote 1.2kW max power, which at 12v input would be 100A. Their max input rating is given as 20A, so 240W max input power. Pulling this level of power from such a cheaply designed converter isn’t going to be reliably possible, the input terminals aren’t even rated to anywhere near 20A, so these would be the first to melt, swiftly followed by everything else. Some of these units come with a fan fitted from the factory, but these are as cheaply made as possible, with bearings made of cheese. As a result they seize solid within a couple of days of use.
Proper converters from companies like TDK-Lambda or muRata rated for these power levels are huge, with BOLTS for terminals, but they’re considerably more expensive. These Chinese units are handy though, as long as they are run at a power level that’s realistic.
A big thanks to my grandad, the collector of all the things, breeder of tropical fish & budgies. A rock of the family for my 29 years on this earth, and who took me in for 5 years during a particularly difficult time of my life, and supported me entirely. It has been an honour to return that kindness in helping you complete your final journey to a funeral I am certain you would have liked. You will be very sorely missed now you’re gone, but you will never be forgotten.
Yesterday, the Raspberry Pi community got a nice surprise – a new Pi! This one has some improved features over the previous RPi 3 Model B:
Improved CPU – 64-Bit 1.4GHz Quad-Core BCM2837B0
Improved WiFi – Dual Band 802.11b/g/n/ac. This is now under a shield on the top of the board.
Improved Ethernet – The USB/Ethernet IC has been replaced with a LAN7515, supporting gigabit ethernet. The backhaul is still over USB2 though, so this would max out at about 300Mbit/s
PoE Support – There’s a new 4-pin header, and a matching HAT for power over ethernet support.
Chipset
The USB/LAN Controller is now a BGA package, supporting gigabit ethernet. The USB connections are still USB2 though, limiting total bandwidth. This shouldn’t be much of an issue though, since anything over the 100Mbit connection we’ve had previously is an improvement.
CPU & Radio
The CPU now has a metal heatspreader on top of the die, no doubt to help with cooling under heavy loads. As far as I know, it’s still the same silicon under the hood though. The WiFi radio is under the shielding can to the top left, with the PCB trace antenna down the left edge of the board.
Power Controller
The power supplies are handled on this new Pi by the MaxLinear MxL7704, from what I can tell from MaxLinear’s page, it seems to be somewhat of a collaborative effort to find something that would do the best job, since they apparently worked with the Foundation to get this one right. This IC apparently includes four synchronous step-down buck regulators that provide system, memory, I/O and core power from 1.5A to 4A. An on-board 100mA LDO provides clean 1.5V to 3.6V power for analog sub-systems. This PMIC utilizes a conditional sequencing state machine that is flexible enough to meet the requirements of virtually any processor.
PCB Bottom
The bottom of the PCB has the Elpida 1GB RAM package, which is LPDDR2, along with the MicroSD slot.
A quick benchmark running Raspbian Lite & a SanDisk Ultra 32GB Class 10 SD card gives some nice results:
Here’s another domestic CO Alarm, this one a cheaper build than the FireAngel ones usually use, these don’t have a display with the current CO PPM reading, just a couple of LEDs for status & Alarm.
Rear
This alarm also doesn’t have the 10-year lithium cell for power, taking AA cells instead. The alarm does have the usual low battery alert bleeps common with smoke alarms though, so you’ll get a fair reminder to replace them.
Internals
Not much at all on the inside. The CO sensor cell is the same one as used in the FireAngel alarms, I have never managed to find who manufactures these sensors, or a datasheet for them unfortunately.
PCB Top
The top of the single sided PCB has the transformer for driving the Piezo sounder, the LEDs & the test button.
PCB Bottom
All the magic happens on the bottom of the PCB. The controlling microcontroller is on the top right, with the sensor front end on the top left.
Circuitry Closeup
The microcontroller used here is a Microchip PIC16F677. I’ve not managed to find datasheets for the front end components, but these will just be a low-noise op-amp & it’s ancillaries. There will also be a reference voltage regulator. The terminals on these sensors are made of conductive plastic, probably loaded with carbon.
Sensor Cell & Piezo Disc
The expiry date is handily on a label on the back of the sensor, the Piezo sounder is just underneath in it’s sound chamber.
Here a tape is installed in the printer. This unit can handle tape widths up to 18mm. The pinch rollers are operated by the white lever at the top of the image, which engages with the back cover.
Li-Ion Battery
This printer is supplied with a rechargeable battery pack, but AA cells can be used as well. Some of the AA battery terminals can be seen above the battery.
Battery Specs
Pretty standard fare for a 2-cell lithium pack. The charging circuitry doesn’t appear to charge it to full voltage though, most likely to get the most life from the pack.
Cartridge Slot
With the cartridge removed, the printer components can be seen. As these cartridges have in effect two rolls, one fro the ribbon & one for the actual label, there are two drive points.
Pinch Rollers & Print Head
The thermal print head is hidden on the other side of the steel heatsink, while the pinch rollers are on the top right. The plastic piece above the print head heatsink has a matrix of switches that engage with holes in the top of the label cartridge, this is how the machine knows what size of ribbon is fitted.
Mainboard
Most of the internal space is taken up by the main board, with the microprocessor & it’s program flash ROM top & centre.
Charger Input
The charger input is located on the keyboard PCB just under the mainboard, which is centre negative, as opposed to 99% of other devices using centre positive, the bastards.
LCD Module
The dot-matrix LCD is attached to the mainboard with a short flex cable, and from the few connections, this is probably SPI or I²C.
Print Mech Drive
The printer itself is driven by a simple DC motor, speed is regulated by a pair of photo-interrupters forming an encoder on the second gear in the train.
Battery Holder Connections
The back case has the battery connections for both the lithium pack & the AA cells, the lithium pack has a 3rd connection, probably for temperature sensing.
Since I do my own PCBs on a somewhat regular basis, I decided it was time to move to a more professional method to etch my boards. I have been using the cheap toner transfer method, using special yellow coated paper from China. (I think it’s coated in wax, or some plastic film).
The toner transfer paper does usually work quite well, but I’ve had many issues with pinholes in the transfer, which cause the etched tracks to look horrid, (not to mention the potential for breaks & reduced current capacity), and the toner not transferring properly at all, to issues with the paper permanently fusing to the copper instead of just transferring the toner.
BigClive has done a couple of fairly comprehensive videos on the dry film photoresist available from AliExpress & eBay. This stuff is used similarly to the toner transfer method, in that the film is fused to the board with heat, but then things diverge. It’s supplied either in cut sheets, or by the roll. I ordered a full roll to avoid the issues I’ve heard of when the stuff is folded in the post – once it’s creased, it’s totally useless. The dry film itself is a gel sandwiched between two protective plastic film sheets, and bonds to the board with the application of heat from a laminator.
The board is first cleaned with scotchbrite pad & soap to remove any tarnish & oil from the copper.
Dry Film
Once the board has been cleaned, one side of the backing film is removed from the gel with adhesive tape, and the dry film is placed on the board while still wet. This stops the film from sticking immediately to the clean copper, one edge is pressed down, and it’s then fed through a modified laminator:
Modified Laminator
I’ve cut away most of the plastic covering the hot rollers, as constant jamming was an issue with this cheapo unit. All the mains power is safely tucked away under some remaining plastic cover at the end. The board with it’s covering of dry film is fed into the laminator – the edge that was pressed down first. This allows the laminator to squeeze out any remaining water & air bubbles from between the two so no creases or blisters form.
After Lamination
Once the board has been run through the laminator about 6 times, (enough to get it very hot to the touch), the film is totally bonded to the copper. The top film is left in place to protect the UV sensitive layer during expsure.
Photomask
The exposure mask is laser printed onto OHP transparencies, in this case I’ve found I need to use two copies overlaid to get enough opacity in the black toner sections to block the UV light. Some touching up with a Sharpie is also easy to do if there are any weak spots in the toner coverage. This film is negative type – All the black areas will be unexposed and washed off in the developer tank. I also found I had to be fairly generous with track spacing, using too small lines just causes issues with the UV curing bits of film it isn’t supposed to.
Exposing The PCB
The PCB is placed on a firm surface, the exposure mask lined up on top, and the whole thing covered with a sheet of standard glass to apply even pressure. The UV exposure lamp in this case is a cheap eBay UV nail curing unit, with 15 high power LEDs. (I’ll do a teardown on this when I get some time, it’s got some very odd LEDs in it). Exposing the board for 60 seconds is all the time needed.
After Exposure
After the board is exposed, the areas that got hit with the UV light have turned purple – the resist has hardened in these areas. It’s bloody tough as well, I’ve scrubbed at it with some vigour and it doesn’t come off. Toner transfer was a bit naff in this respect, most of the time the toner came off so easily that the etchant lifted it off. After this step is done, the remaining protective film on the top can be removed.
After Developing
The film is developed in a solution of Sodium Carbonate (washing Soda). This is mildly alkaline and it dissolves off the unexposed resist.
After Etching
Now it’s into the etching tank for a couple of minutes, I’m still using Ferric Chloride to etch my boards, at about 60°C. Etching at room temperature is much too slow. Once this is done, the board is washed, and then dipped in the strip tank for a couple of minutes. This is a Sodium Hydroxide solution, and is very caustic, so gloves are required for this bit. Getting Ferric Chloride on skin is also a fairly bad idea, it stains everything orange, and it attacks pretty much every metal it comes into contact with, including Stainless Steel.
This method does require some more effort than the toner transfer method, but it’s much more reliable. If something goes wrong with the exposure, it’s very easy to strip the board completely & start again before etching. This saves PCB material and etchant. This is definitely more suited to small-scale production as well, since the photomask can be reused, there’s much less waste at the end. The etched lines are sharper, much better defined & even with some more chemicals involved, it’s a pretty clean process. All apart from the Ferric Chloride can be disposed of down the sink after use, since the developer & stripper are just alkaline solutions.
The rear has the specifications, laser-marked into the plastic. The serial numbers are just sticky labels though, and will come off easily with use.
Contec CMS-50F
This is the Contec CMS-50F wrist-mounted pulse oximeter unit, which has the capability to record data continuously to onboard memory, to be read out at a later time via a USB-Serial link. There is software supplied with the unit for this purpose, although it suffers from the usual Chinese quality problems. The hardware of this unit is rather well made, the firmware has some niggles but is otherwise fully functional, however the PC software looks completely rushed, is of low quality & just has enough functionality to kind-of pass as usable.
Top Cover Removed
A total of 4 screws hold the casing together, once these are removed the top comes off. The large colour OLED display covers nearly all of the board here. The single button below is the user interface. The connection to the probe is made via the Lemo-style connector on the lower right.
Lithium Cell
Power is provided by a relatively large lithium-ion cell, rated at 1.78Wh.
Main Processor
All the heavy lifting work of the LCD, serial comms, etc are handled by this large Texas Instruments microcontroller, a MSP430F247. The clock crystal is just to the left, with the programming pins. I’m not sure of the purpose of the small IC in the top left corner, I couldn’t find any reference to the markings.
Aux Processor
The actual pulse oximetry sensor readings seem to be dealth with by a secondary microcontroller, a Texas Instruments M430F1232 Mixed-Signal micro. This has it’s own clock crystal just underneath. The connections to the probe socket are to the right of this µC, while the programming bus is broken out to vias just above. The final devices on this side of the board are 3 linear regulators, supplying the rails to run all the logic in this device.
Main PCB Rear
The rear of the PCB has the SiLabs CL2102 USB-Serial interface IC, the large Winbond 25X40CLNIG 512KByte SPI flash for recording oximetry data, and some of the power support components. The RTC crystal is also located here at the top of the board. Up in the top left corner is a Texas Instruments TPS61041 Boost converter, with it’s associated components. This is probably supplying the main voltage for the OLED display module.
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