The Engineer – Page 12 – Experimental Engineering

Posted on October 23, 2015 by The Engineer — Leave a comment

Another Chinese Charger

I almost forgot about this bit of kit, that came with one of my LED torches as a Lithium Ion charger. As I never plug in anything that comes from China via eBay, here’s the teardown & analysis.

Here’s the unit itself. It’s very light, and is clearly intended for American NEMA power points.

Claimed specifications are 100-240v AC input, making it universal, and 4.2v DC out ±0.5v at 500mA.
Considering the size of the output wire, if this can actually output rated voltage at rated current I’ll be surprised.

Here’s the adaptor opened up. There’s no mains wiring to speak of, the mains pins simply push into tags on the PCB.

Top of the SMPS PCB. As usual with Chinese gear, it’s very simple, very cheap and likely very dangerous. There’s no real fusing on the mains input, only half-wave rectification & no EMI filtering.

Here’s the bottom of the PCB. At least there’s a fairly sized gap between the mains & the output for isolation. The wiggly bit of track next to one of the mains input tags is supposed to be a fuse – I somehow doubt that it has the required breaking characteristics to actually pass any safety standards. Obviously a proper fuse or fusible resistor was far too expensive for these.

The output wiring on the left is thinner than hair, I’d say at least 28AWG, and probably can’t carry 500mA without suffering extreme volt drop.

Posted on October 22, 2015 by The Engineer — Leave a comment

Netgear GS308 Gigabit Switch

Here’s a new addition to the network, mainly to replace the ancient Cisco Catalyst 3500 XL 100MB switch I’ve been using for many years, until I can find a decently priced second hand commercial gigabit switch.

Here’s the switch with some network connections on test. So far it’s very stable & draws minimum power. I’ve not yet attempted to run my core links (NAS) through yet, as I’ve not yet seen a consumer grade switch that can stand up to constant full load without crashing.

Here’s the switch with it’s lid popped. The magnetics can be seen at the back, next to the RJ-45 ports, the large IC in the centre is the main switching IC, with a heatsink bonded to the top. Very minimal design, with only a couple of switching regulators for power supply & not much else.

Here’s a closeup of some of the support components. There’s a 25MHz crystal providing a clock signal for the switch IC, just to the right of that is an EEPROM. I imagine this is storing the switch configuration & MAC address. Further right is one of the switching DC-DC converter ICs for power.

As a quick test, here’s 500GB of data being shifted through the switch, at quite an impressive rate. I’m clearly maxing out the bandwidth of the link here. Soon I will upgrade to a 10G Ethernet link between the NAS & main PC to get some more performance.

Posted on October 20, 2015 by The Engineer — Leave a comment

5-Port HDMI Switch

Here’s another quick teardown, a cheap 5-port HDMI switch box. This is used to allow a single input on a monitor to be used by 5 different external HDMI devices, without having to mess about plugging things in.

Here’s the DC barrel jack & 3.5mm TRS jack for power & remote control. There’s a little IR decoder & remote that go with this for hands free switching.

Here’s the PCB out of it’s plastic housing. The main logic is a pair of PI3HDMI303 3:1 HDMI switches from Pericom Semiconductor. These are cascaded for the 5-ports, the first 3 input HDMI ports are switched through both ICs to reach the output.
These HDMI switch ICs are operated with TTL input pins, the combination of these pins held either high or low determines the input port that appears on the output.
There’s a button on the left for switching between inputs, with a row of 5 LED indicators.

Not much on the bottom side, a lot of passives & bypass capacitors. There’s a 3.3v LDO regulator on the left for supplying the main rail to the active switch ICs. The IC on the right doesn’t have any numbering at all, but I’m presuming it’s a microcontroller, dealing with the IR remote input & pushbutton inputs to switch the inputs.

Posted on October 20, 2015 by The Engineer — Leave a comment

Maplin/Refrakta Torch Modification & Mode Removal

The multimode dimming/flashing modes on Chinese torches have irritated me for a while. If I buy a torch, it’s to illuminate something I’m doing, not to test if people around me have photosensitive epilepsy.

Looking at the PCB in the LED module of the torch, a couple of components are evident:

There’s not much to this driver, it’s simply resistive for LED protection (the 4 resistors in a row at the bottom of the board).
The components at the top are the multimode circuitry. The SOT-23 IC on the left is a CX2809 LED Driver, with several modes. The SOT-23 on the right is a MOSFET, for switching the actual LED itself. I couldn’t find a datasheet for the IC itself, but I did find a schematic that seems to match up with what’s on the board.

Here’s that schematic, the only thing that needs to be done to convert the torch to single mode ON/OFF at full brightness, is to bridge out that FET.

To help save the extra few mA the IC & associated circuitry will draw from the battery, I have removed all of the components involved in the multimode control. This leaves just the current limiting resistors for the LED itself.

The final part above, is to install a small link across the Drain & Source pads of the FET. Now the switch controls the LED directly with no silly electronics in between. A proper torch at last.

Posted on October 20, 2015October 18, 2015 by The Engineer — Leave a comment

DIY SMPS Fan Controller

Now the controllers have arrived, I can rejig the supplies to have proper thermal control on their cooling.

Here’s the top off the PSU. The board has been added to the back panel, getting it’s 12v supply from the cable that originally fed the fan directly. Luckily there was just enough length on the temperature probe to fit it to the output rectifier heatsink without modification.

To connect to the standard 4-pin headers on the controller, I’ve spliced on a PC fan extension cable, as these fans spent their previous lives in servers, with odd custom connectors.

Here’s the controller itself, the temperature probe is inserted between the main transformer & the rectifier heatsink.
I’ve set the controller to start accelerating the fan at 50°C, with full speed at 70°C.

Under a full load test for 1 hour, the fan didn’t even speed up past about 40% of full power. The very high airflow from these fans is doing an excellent job of keeping the supply cool. Previously the entire case was very hot to the touch, now everything is cool & just a hint of warm air exits the vents. As the fan never runs at full speed, the noise isn’t too deafening, and immediately spools back down to minimum power when the load is removed.

Posted on October 18, 2015 by The Engineer — 7 Comments

Maplin/Refrakta XR-E LED Torch

Following on from the teardown & analysis of the charger, here’s the torch itself under the spotlight.

Here’s the torch itself, it’s a sturdy device, made of aluminium. Power is provided by a single 18650 Li-Ion cell.

Here’s the charging port on the torch, there’s no electronics in here for controlling the charge, the socket is simply connected directly to the Li-Ion cell, and requires a proper external charger.

Unscrewing the lens gives access to the LED core, this also unscrews from the torch body itself, leaving the power switch & the battery in the body.

Unscrewing the aluminised plastic reflector reveals the LED itself. Being a new device, I expected an XM-L or XM-L2 Cree LED in here, but it’s actually an XR-E model, a significantly older technology, rated at max 1A of drive current.

Popping the control PCB out from the pill reveals a lot of empty space, but the back of the LED is completely covered by a heatsinking plate, which is conducting heat to the main body of the torch.

Not much to see on the control PCB, just a bunch of limiting resistors, and a multi-mode LED driver IC in a SOT-23 package. There’s no proper constant-current LED driver, and as the battery discharges the torch will dim, until the low voltage cutout on the cell turns things off completely.

Posted on October 18, 2015October 18, 2015 by The Engineer — Leave a comment

Timelapse Canal Trip – Marple To Macclesfield

Here’s the videos from this weekend’s canal trip, from our mooring at Marple to just outside Macclesfield center.

Posted on October 15, 2015October 16, 2015 by The Engineer — Leave a comment

DIY SMPS Fan Speed Control – The Controllers

Finally, after a couple of weeks wait time, the fan controllers for the power supplies have arrived. They’re small boards, which is good for the small space left inside the case of the supply.

Here they are. I’m not certain what the pair of potentiometers are for – there’s no mention of them in the documentation. Possibly for calibration.
Beepers are supplied so an alarm can be heard if the fan fails – very useful for this application.

Here’s a closeup of the PCB. Options are set with the DIP switch bank on the left, details for that below. The main IC is a STM8S103F3 flash microcontroller.

The only issue at the moment is that the temperature probe leads are much too short. I’ll have to make a small modification to get enough length here.

Here’s all the details on the boards, more for future reference when they undoubtedly vanish from eBay 😉

Specifications

Working voltage:DC12V

Circuit load capacity: maximum current per output 5A, the bus currents up 9A

Output Range: The first channel 20% -100%, or 40% -100% (TFL = ON)
The second channel and the third channel 10% -100%

(Note: Above range only for PWM range, the actual control effect will vary depending on the fan.)

Temperature probe parameters: 50K B = 3950

Thermostat temperature zone error: error depending on the temperature probe, generally 3-5%

Stall alarm minimum speed: 700-800 rpm

Function setting switch Description:

TFL (No. 1): The lowest temperature channel PWM setting, when ON state FAN1 PWM minimum is 40%, when OFF the minimum PWM of FAN1 is 20%.

TP1 TP2 (No. 2,3): Temperature channel control temperature zones are interpreted as follows (need to used with the temperature probe):

TP1	TP2	Accelerating temperature	Full speed temperature
OFF	OFF	35℃	45℃
ON	OFF	40℃	55℃
OFF	ON	50℃	70℃
ON	ON	60℃	90℃

When the temperature lower than the accelerated temperature, then output at the minimum rotation speed; when it exceed over the full temperature, then always output at full speed.

BF1 BF2 (No. 4,5): corresponds FAN1 FAN2 stall alarm function switch, when the corresponding open channel fan break down, the controller will alarm with soundand light (works with buzzle), alarm will automatically eliminated when the fan is rotated recovery . If BF1 and BF2 both are open (ON), the FAN1, FAN2 have any one or both stops, the controller will alarm!

Posted on October 13, 2015October 15, 2015 by The Engineer — Leave a comment

Raspberry Pi Timelapse Video Generator Script & Full Script Pack Download

To cap off the series of scripts for doing easy timelapse video on the Raspberry Pi, here’s a script to generate a H.264 video from the images.

[snippet id=”1771″]

This should be run on a powerful PC rather than the Pi – generating video on the Pi itself is likely to be very slow indeed.

I have also done a quick update to the timelapse generator script to generate images of the correct size. This helps save disk space & the video generation doesn’t have to resize the images first, saving CPU cycles.

[snippet id=”1768″]

[download id=”5595″]

73s for now!

Posted on October 13, 2015 by The Engineer — Leave a comment

eBay Special 2.5″ HDD USB Case

Since I have a fair few 750GB disks sat doing nothing, I figured I’d get some USB3 caddies for them. Back when USB -> IDE caddies appeared, they were hideously expensive. Not so much these days!

For £6 on eBay, you get a basic plastic box with the required bridge circuitry.

Here’s the PCB – a very basic affair, with only 2 ICs. The large QFN IC on the left is the USB-SATA bridge. It’s a JMicron JMS567. Unfortunately JMicron are rather secretive about their bridge chips & I can’t find much information about it, nor a datasheet.

Here’s the other side of the bridge PCB – not much on here, the activity indicator LED is a bit of a bodge job, but it’s functional. The IC on the right is a Pm25LD512 512Kbit SPI EEPROM. This is used to store things like the USB device & vendor IDs, device name, type, etc. Here’s what dmesg spits out when the disk is connected on my standard Linux system:

[snippet id=”1769″]

Here’s some speed benchmarks:

First attached to a USB2 port, above

And finally attached to a USB3 port, above

Tests were done with a 320GB 5400RPM Samsung HM321HI drive, direct into the root hub, for the shortest possible signal length.

Posted on October 13, 2015 by The Engineer — Leave a comment

Raspberry Pi Timelapse – Resequencing Images

Sometimes while taking timelapse video on the Pi, it misses frames, for no apparent reason. I have been playing with various combinations of disks/SATA cases to see what the bottleneck is. Oddly enough a faster drive actually made the problem worse!

Here’s an example of some really bad frame skipping, this is with a frame interval of 1250ms, which has worked fine in the past. The disk used is a 750GB WD Black 7200RPM, so disk access time shouldn’t be an issue.

Since frame skipping is rarely a problem in timelapse video I do, I’ve been searching for something to automatically renumber all the frames for processing into video – after writing my own script, which was a bit crusty, I came across a very handy script on SourceForge. It required a couple of small modifications to work correctly with what I want, but here’s the slightly modified version.

[snippet id=”1770″]

With the small modifications, it renumbers the images correctly for processing by AVConv.

More scripting to come when I sort out an automatic transcode kludge!

73s for now

Posted on October 11, 2015 by The Engineer — Leave a comment

nb Tanya Louise Drive Coupling Replacement – The Final Install

It’s time for the final part of getting the boat’s engine & drive back together, now I have the new coupling hub. I decided to address one of the issues with the pump mounting while I had everything in bits. When the hydraulic drive was installed, a custom plate was laser cut to fit the pump stack to, as we had no bellhousing with a standard mounting pattern.

Even though this plate is 10mm steel, under full load it actually bends – so to strengthen it along the long edge, I have welded a pair of ribs to the plate.

The mounting plate as removed from the mounting brackets. The slotted holes at the sides allow for some movement to adjust the position of the pump & flywheel coupling.

I ground off the paint & grease with an abrasive disc, and am replacing one of the pump mounting studs while I’m at it.

Here’s the plate after welding. a pair of 10mm bars have been attached along the edges, this will give the mounting significantly more strength on the long axis & prevent any deformation.

Here the plate has been loosely mounted on it’s brackets, & I’ve got the pump stack with it’s associated tangle of hoses on the chain hoist. This unit is very heavy on it’s own – a 2 man job to lift it into place on it’s mounts – with the very stiff hydraulic hoses attached & filled with oil it’s absolutely unmanageable.

Here the pump is being jostled into place. The central hole in the mounting plate is a very snug fit, if the pump doesn’t go in exactly straight it will jam & cause damage to both parts. The mating hole in the coupling hub can be seen here – it’s not quite lined up yet.

We’ve got about 10mm to go before the pump is seated. It’s held in place with a pair of large studs & nuts.

Here the pump is fitted enough to get the main mounting bolts into the coupling. These are torqued down to 150ft/lbs – a difficult thing to do considering the restricted space in the engine bay.

The pump has been pulled down onto the plate evenly with the mounting studs, and is now completely flush with the plate. As can be seen, I didn’t bother tidying up the welds with a grinder, they aren’t in any visible place in normal operation, so it didn’t warrant the effort.

Finally, the control cable is reattached to the pump’s control lever & everything is installed! A short test trip proved that everything was stable & no undue movement of the pump or coupling was noticed.

Until next time, 73s!

Posted on October 11, 2015October 11, 2015 by The Engineer — Leave a comment

Raspberry Pi Timelapse Script

To make my timelapse video capture a little easier, I wrote a small script that handles creation of a new folder for every timelapse instance, deals with the runtime & frame interval flags & generally makes everything a little cleaner.

As with most of my code, it’s rough, but functional

[snippet id=”1768″]

[download id=”5593″]

Posted on October 7, 2015 by The Engineer — Leave a comment

Maplin LED Torch Charger Replacement

In my previous post, I mentioned I’d be replacing the factory supplied charging gear with something that actually charges lithium chemistry cells correctly.

Here’s the base as supplied, with an indicator LED on the right hand side. This LED indicates nothing other than power being applied to the charging base. It’s just connected across the power input with a resistor. This also means that any battery left in the charger while it’s unplugged will discharge itself through this LED over time. Great design there China!

Here I’ve removed the PCB – there’s no need for it to be taking up any space, as it’s just a complete waste of copper clad board in the first place. The battery tabs have been desoldered & hot snot used to secure them into the plastic casing.

The charger modules I use are USB powered, so a small hole has been routed out in the casing to allow access to the port.

Here the charging module has been installed & wired to the battery tabs. Output is now a nice 4.18v, and will automatically stop charging when the cell is full.
Safety has been restored!

73s for now folks!

Posted on October 7, 2015 by The Engineer — Leave a comment

Maplin 3W LED Torch Charger Fail

A member of the family recently bought one of these torches from Maplin electronics, and the included chargers for the 18650 lithium-ion cells leave a lot to be desired.

Here’s what’s supplied. The torch itself is OK – very bright, and a good size. Me being cynical of overpriced Chinese equipment with lithium batteries, I decided to look in the charging base & the cigar-lighter adaptor to see if there was any actual charging logic.

Answer – nope. Not a single active component in here. It’s just a jack connected to the battery terminals. There’s all the space there to fit a proper charging circuit, but it’s been left out to save money.

OK then, is it inside the cigarette lighter adaptor?

Nope. Not a single sign of anything resembling a Lithium-Ion charger IC. There’s a standard MC34063A 1.5A Buck converter IC on the bottom of the PCB, this is what’s giving the low voltage output for the torch.

Here’s the IC – just a buck converter. The output voltage here is 4.3v. This is higher than the safe charging voltage of a lithium ion cell, of 4.2v.

The cells supplied are “protected” versions, having charge/discharge protection circuitry built onto the end of the cell on a small PCB, this makes the cell slightly longer than a bare 18650, so it’s easy to tell them apart.
The manufacturers in this case are relying on that protection circuit on the cell to prevent an overcharge condition – this isn’t the purpose they’re designed for, and charging this way is very stressful for the cells. I wouldn’t like to leave one of these units charging unattended, as a battery explosion might result.

More to come shortly when I build a proper charger for this torch, so it can be recharged without fearing an alkali metal fire!

73s for now folks!

Posted on October 6, 2015 by The Engineer — Leave a comment

nb Tanya Louise Propulsion Rebuild – Part 1

Time to get on with the job now the parts have arrived! Above is the new coupling hub, as can be seen compared to the old one that I previously posted about, this one has it’s full complement of splines.

The hub bolts into the centre of this rubber coupling, which itself locates on pins attached to the engine’s flywheel. This part wasn’t damaged so it’s being reused with the new hub.

Here’s the hub installed on the input shaft of the main hydraulic pump stack, the pair of holes on the side of the hub are for the grub screws that secure the coupling on the splines. These screws coming loose are what destroyed the old coupling.

Here’s the engine flywheel, where the rubber coupling normally sits. The mounting pins have been greased ready to accept the rest of the coupling.

Here’s the rubber element mounted on the pins – there’s nothing holding it there in normal operation apart from the mating side of the coupling with the pump.

Unfortunately the weather here in Manchester has prevented us from getting any further – more t0 come when the rain stops!

73s for now folks!

Posted on October 6, 2015 by The Engineer — Leave a comment

µRadMonitor RRDTool Graphing

I’ve been meaning to sort some local graphs out for a while for the radiation monitor, and I found a couple of scripts created by a couple of people over at the uRadMonitor forums for doing exactly this with RRDTool.

Using another Raspberry Pi I had lying around, I’ve implemented these scripts on a minimal Raspbian install, and with a couple of small modifications, the scripts upload the resulting graphs to the blog’s webserver via FTP every minute.

[snippet id=”1759″]

This script just grabs the current readings from the monitor, requiring access to it’s IP address for this.

[snippet id=”1760″]

This script sets up the RRDTool data files & directories.

[snippet id=”1761″]

The final script here does all the data collection from the monitor, updates the RRDTool data & runs the graph update. This runs from cron every minute.
I have added the command to automate FTP upload when it finishes with the graph generation.

This is going to be mounted next to the monitor itself, running from the same supply.

The Graphs are available over at this page.

Posted on October 6, 2015 by The Engineer — Leave a comment

Power Supply Cooling Update

While I’m waiting for the fan controllers to arrive for the new cooling fans, I figured I’d get them fitted into the cases of the supplies & just have them run at minimum speed for now.

After removing the original small fan, I cut a larger square hole in the panel to fit the 60mm version. These fans only fit with some minor adjustment to the top & bottom mouldings, but the look isn’t too bad once the covers are back on. The wiring is routed through a small hole next to the fan itself.

I’ve also upgraded on the fans again – these are PFC0612DE, with a higher airflow of ~70CFM at 12,000RPM.

To get the fans to run at minimum speed, the PWM control wire is connected directly to GND.

More to come when the controllers arrive!

Posted on October 1, 2015 by The Engineer — 10 Comments

3M Microtouch 17″ Raspberry Pi Touch PC

A while back I posted about a 3M Touch Systems industrial monitor that I’d been given. I had previously paired it with a Raspberry Pi Model B+, but for general desktop use it was just a little on the slow side.

Since the release of the Raspberry Pi 2, with it’s 4-core ARM Cortex CPU, things are much improved, so I figured I’d post an update with the latest on the system.

The monitor I’ve used is a commercial one, used in such things as POS terminals, service kiosks, etc. It’s a fairly old unit, but it’s built like a tank.

It’s built around a Samsung LTM170EI-A01 System-On-Panel, these are unusual in that all the control electronics & backlighting are built into the panel itself, instead of requiring an external converter board to take VGA to the required LVDS that LCD panels use for their interface.

The touch section is a 3M Microtouch EXII series controller, with a surface capacitive touch overlay.

Above is the touch controller PCB, with it’s USB-Serial converter to interface with the Pi.

As there is much spare space inside the back of this monitor, I have mounted the Pi on a couple of spare screw posts, fitted USB ports where the original VGA & Serial connectors were in the casing, and added voltage regulation to provide the Pi with it’s required 5v.

Here’s the entire back of the panel, the Pi in the middle interfaces with a HDMI-VGA adaptor for the monitor, and the serial adaptor on the right for the touch. A small voltage regulator at the bottom of the unit is providing the 5v rail. There’s a switch at the bottom next to one of the USB ports to control power to the Pi itself. The panel won’t detect the resolution properly if they’re both powered on at the same time.

At 13.8v, the device pulls about 2A from the supply, which seems to be typical for a CCFL backlighted LCD.
Now the Raspberry Pi 2 has been released, it’s much more responsive for desktop applications, especially with a slight overclock.

A full disk image enabled for Desktop & 3M touch monitors is available below for others that have similar panels. This image only works for the Pi 2!

[download id=”5591″]

Posted on September 28, 2015 by The Engineer — Leave a comment

nbTanya Louise Drive Failure

As I have posted about before, the main propulsion system onboard the boat is all hydraulic. To get the drive from the flywheel of the engine to the hydraulic pump stack, a custom drive plate was machined by Centa Transmissions over in Yorkshire, and a Centaflex A coupling was fitted to this.

This coupling is a big rubber doughnut, bolted to a centre hub of steel. The steel hub is splined onto the input shaft of the hydraulic pump stack.

The problem we’ve had is that to prevent the coupling from riding along the splines in operation, a pair of giant grub screws are provided in the side of the centre steel boss, that compress the splines to lock the device in place. These screws are a nightmare to get tightened down (the engineer from Centa who originally came to survey the system said we’d probably shear some tools off trying).

Because of this, the grub screws have loosened over the last 350-odd hours of running & this has had the effect of totally destroying the splines in the hub.

Here’s the backside of the centre boss, with what remains of the splines, the figure-8 shaped gap on the right is where the securing grub screws deform the steel to lock the coupling into place.

Here’s the other side of the coupling, showing the damage. The splines have effectively been totally removed, as if I’d gone in there with a boring bar on the lathe. Luckily this part isn’t too expensive to replace, and no damage was done to the input shaft of the hydraulic pump stack (Mega ££££). Quite luckily, this damage got to the point of failure while running the engine on the mooring, so it didn’t leave us stranded somewhere without motive power.

More to come when the new coupling arrives!

Posted on September 27, 2015 by The Engineer — Leave a comment

DIY SMPS Cooling

The power supplies I have recently built from surplus Cisco switch boards have started displaying a rather irritating problem – continual load of over 9A causes the supplies to shut down on overheat.

This was partially expected, as the original switches that these supplies came from are cooled by a monster of a centrifugal blower that could give a Dyson a run for it’s money. The problem with these fans is that they’re very loud, draw a lot of power (3-4A) and aren’t small enough to fit into the case I’ve used for the project.

The solution of course, is a bigger fan – I’ve got some Delta AFB0612EHE server fans, these are very powerful axial units, shifting 60CFM at 11,000RPM, with a power draw of 1.12A.
They’re 60mm diameter, so only just fit into the back of the case – although they stick out of the back by 40mm.

Here’s the fan, not the beefiest I have, but the beefiest that will fit into the available space.
These will easily take fingers off if they get too close at full speed, so guards will definitely be required.

To reduce the noise (they sound like jet engines at full pelt), I have ordered some PWM controllers that have a temperature sensor onboard, so I can have the fan run at a speed proportional to the PSU temperature. I will probably attach the sensor to the output rectifier heatsink, since that’s got the highest thermal load for it’s size.

More to come when parts arrive!

73s for now 🙂

Posted on September 22, 2015 by The Engineer — Leave a comment

Dell SE197FPf Monitor 12v Conversion

My other monitors are a different model, and have a slightly different main PCB inside, but the process is mostly the same for converting these to 12v supply.

In this monitor type, there is only a single board, with all the PSU & logic, instead of separate boards for each function.

This monitor is slightly different in it’s power supply layout. The mains supply provides only a single 12v rail, which is then stepped down by a switching converter to 5v, then by smaller linear regulators to 3.3v & 1.8v for the logic. This makes my life easier since I don’t have to worry about any power conversion at all.

Here’s the backside of the PCB, the mains PSU section is in the centre.

Here’s the pair of 12v supply wires soldered onto the main board, onto the common GND connection on the left, and the main +12v rail on the right. I’ve not bothered with colour coding the wiring here, just used whatever I had to hand that was heavy enough to cope with a couple amps.

A small mod later with a cone drill & the 12v input socket is mounted in the LCD frame.

Some light removal of plastic & the back cover fits back on. Current draw at 13.8v is ~2A.

Posted on September 21, 2015 by The Engineer — 1 Comment

Dell E207WFPc Monitor 12v Conversion

I’m still on my crusade of removing every trace of 240v mains power from my shack, so next up are my computer monitors.

I have 4 Dell monitors, of various models, hooked up to my main PC.

The monitor here is a Dell E207WFPc 20″ widescreen model. There will be more when I manage to get the others apart to do the conversion. However I’m hoping that the PSU boards are mostly the same.

There are no screws holding these monitors together, the front bezel is simply clicked into place in the back casing, these clips are the only thing that holds the relatively heavy glass LCD panel & it’s supporting frame! The image above shows the panel removed. The large board on the left is the power supply & backlight inverter, the smaller one on the right is the interface board to convert the DVI or VGA to LVDS for the LCD panel itself.

Here’s a closeup of the PSU board, the connector at centre right at the top of the PCB is the main power output, and also has a couple of signals to control the backlight inverter section of the PSU, on the left side. The PSU requirements for this monitor are relatively simple, at 14.5v for the backlight & 5v for the logic board.

Here’s the top of the PSU board, very simple with the mains supply on the right side, and the backlight inverter transformers on the left.

Here I’ve hooked into the power rails on the supply, to attach my own 12v regulators. The green wire is +14.5v, and the purple is +5v. Black is common ground.

On doing some testing, the backlight inverter section doesn’t seem to mind voltages between 11.5-14.5v, so a separate regulator isn’t required there. Even running off batteries that’s within the range of both charging & discharging. The only regulator required is a 5v one to reduce the input voltage for the logic PCB.

On applying some 12v power to the regulator input, we have light! Current draw at 12.5v is 2.65A for a power consumption of 33W.

There’s plenty of room in the back casing to mount a 12v input socket, I have left the mains supply intact so it can be used on dual supply.

Here’s the 5v regulator mounted on the back of the casing, all wired up & ready to go.

Posted on September 13, 2015October 16, 2019 by The Engineer — Leave a comment

17mm µMonitor

I’ve had a couple of viewfinder CRT modules for a while, & haven’t done much with them, so I decided to make a very small B&W monitor.

I ordered a small transparent ABS box when I made a large order with Farnell, that turned out to be just about the perfect size for the project! The CRT & PCB barely fit into the space. The face of the CRT itself is about 17mm across.

Here’s the main PCB & tube fully installed into the case. Barely enough room for a regulator left over!
Power is provided by a simple LM7809 IC to take a standard 12v input.

Rear of the case, showing the fit of the control board.

Here’s the back of the monitor, with the DC input jack & a 3.5mm 4-pole jack for audio & video. This allows simple connection to many devices, including the one I’ll use the most – the Raspberry Pi.

Completed monitor. Audio is handled by a very small 20mm speaker, currently mounted just below the CRT face.
Current draw from a 13.8v supply is 117mA.

Posted on September 13, 2015September 13, 2015 by The Engineer — Leave a comment

Rigol DS1054Z DC Power Supply – Linear Post Regulation

Finally, here’s the last part of the Rigol 12v DC Power Supply project, the linear post regulation section to remove some of the ripple.

I have made a couple of layout adjustments since the last post about this part of the project – a little more filtering on the DC outputs. As usual the Eagle project files are at the bottom of the post for those who might find them useful.

Here’s the completed PCB, partially installed in the back of the scope. The missing regulator is the 5v one, since I already have a source of clean 5v from my original attempt at the supply, it’s not a problem not using a linear after the switcher. The filtering is the same on all channels, input from the switchers is on the right, outputs to the scope on the left.

Here’s the bottom of the PCB, with the common mode input chokes. The design of this board has allowed me to remove a couple of the switching modules as well, as I can use a single bipolar supply to run both sets of bipolar regulators on this board. This should help remove some of the noise also.

The ripple level has now dropped to lower than it was originally on the mains supply! Current draw at 13.8v DC is about 1.75A.

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