Having now tested the supply I wrote about in my previous post, I can now say that it’s nameplate rating far exceeds it’s actual capability.
On running the supply under load, at 6.5A the operating frequency drops into the audible range, a big sign of overload. (It makes an irritating continuous chirping noise). The output voltage also drops to 10.5v.
The temperature of the unit while it’s been running under such a load is also questionable, the external casing gets hot enough to cause burns, I haven’t yet been able to stick a thermocouple into the case to see what the internal temperature is.
I’m currently talking with the eBay seller (wwwstation) regarding this, however they are arguing that the supply is only for LEDs & CCTV cameras.
However those two loads are very different, and the supply has no internal regulation for supplying LEDs. As a simple switchmode supply, any load is suitable, providing it’s within the load rating of the supply.
I would estimate that the supply is only capable of 5A as an upper limit.
They are requesting that I return the supply, but I’m yet to find out if they’re going to cover return postage. The item as listed is not as described, and I will escalate things if required.
I will update this post when I hear more back from the eBay seller.
I recently ordered a PSU to run one of the TVs I converted to 12v operation, and being an older TV, it’s a fairly heavy load at 6.5A. eBay to the rescue again, with a cheap 10A rated supply.
Power Brick
Like all similar supplies these days, it’s a SMPS unit, and feels suspiciously light for it’s power rating.
Cover Removed
Luckily this one is easy to get into, no ultrasonic welding on the case, just clips. Here’s the top cover removed, big alloy plate between the heatsinks.
PCB
The top heatsink plate was glued to the top of the transformer with silicone, some gentle prying released it. From the top, things don’t look too bad. There’s some filtering on the mains input & it’s even fused!
Primary Side
Here’s a closeup of the primary side of the PSU, the main DC bus capacitor is a Nichicon one, but it’s clearly been recovered from another device, look at the different glue on the end!
it’s also flapping about in the breeze, the squirt of silicone they’ve put on does nothing to stop movement.
Also here is the mains input fuse, filter capacitor & common mode choke. At least there is some filtering!
The main control IC is a UC3843B High Performance Current Mode PWM Controller, operating at a switching frequency of 250kHz.
The main switching transistor is visible at the bottom left corner, attached to the heatsink.
Secondary Side
Here’s the secondary side of the supply. The transformer itself is OK, nice heavy windings on the output to suit the high current.
It’s using proper opto-isolated feedback for voltage regulation, with a TL431 reference IC.
The output diodes are attached to the heatsink at the top of the photo, I couldn’t read any numbers on those parts.
The output filter capacitors are low quality, only time will tell if they survive. I’ll put the supply under full load & see what the temperature rise is inside the casing.
PCB Bottom
On the bottom of the PCB things get a little more dire. There isn’t really much of an isolation gap between the primary & secondary sides, and there’s a track joining the output negative with mains earth, which gets to within 2mm of the live mains input!
As with all these cheapo supplies, there’s good points & bad points, I will update when I’ve had a chance to put the supply under full load for a while & see if it explodes!
I caught even more abuse on the local repeater this afternoon, this went on for a long time, into the early hours of the morning, having a conversation with himself as per usual. By the sounds of it alcohol was involved, the speech got more slurred as time went on. As usual, here’s the audio for your listening pleasure 🙂
Here we go again with the GB3MR local idiot. He does always try to get a response from people, but we seem to be able to filter out this crap. 🙂 Here’s the audio for your listening pleasure. 🙂
With every piece of Chinese electronics I obtain, mainly Baofeng radios, they come with a Europlug-type power adaptor, and a universal plug adaptor for the mains.
The charger units aren’t too bad, there’s a fair amount of isolation between the primary & secondary, and even though they’re very simple & cheap, I can’t see any immediate safety problems with them.
The plug adaptors, however, are a different matter. These things are utterly lethal!
Baofeng PSU
Here’s the inside of the PSU. It’s just a very simple SMPS, giving an output of 10v 500mA. The fuse is actually a fusible resistor.
PCB Reverse
Here’s the back of the PCB with the SMPS control IC. I can’t find any English datasheets for this part unfortunately.
Universal Travel Adaptor
Here’s the dangerous adaptor. There’s no safety shield, so the live parts are exposed.
Internals
Here’s the adaptor split apart. The output contacts are on the left, and rely just on pressure to make contact with the brass screws on the mains input pins to provide power.
This is a very poor way to get a connection, a dirty or worn contact here would create a lot of heat if any significant power is pulled through, and could quite possibly result in a fire.
Not surprisingly, I bin these things as soon as I open the box, and charge all my radios with a 12v charging system.
Thanks to Lewis over at Distant Signal Radio, the bad influence he is on my bank balance ;), I’m the proud new owner of a new Baofeng. This time it’s the UV-82.
This radio is a little different from the other Baofengs I have. Here are the main differences:
Dual PTT – This one is going to take some getting used to 😉
Higher capacity battery pack
A more rugged, commercial feel
This radio has a different method of selecting the VFO mode – holding the menu key while the unit is powered on. This is a little awkward, but since I only usually use my local repeaters when I’m mobile, it’s not much of an issue.
UV-82
Here’s the radio itself, it has a much more commercial feel to it than the UV-5Rs, and it’s slightly bigger. Mainly due to the use of a larger standard battery & larger loudspeaker.
Spec Label
Back of the unit with the spec label. As per usual Baofeng are a bit conservative with the power ratings, more to come on that below.
Battery Pack
Here’s the battery pack, a 2-cell lithium-polymer unit. This has a bigger capacity than the standard UV-5R battery, at 2800mAh.
Here are the power settings as measured by my GY-561. Frequencies used are 145.500 & 433.500
Here we go again on GB3MR tonight, the guy jumped in after I finished a QSO (which was mainly centred on the Marine VHF band & busy channels).
He’s then going on about legality, but he’s clearly so pissed that I can’t actually get full sentences out of it. Here it is for your listening pleasure.
Came across this today while scanning through frequencies. Not sure of their exact QTH, but there’s references to the Oldham area in Manchester, about as far away as you can get from any marine or commercial shipping area in the county. I didn’t hear any marine callsigns or vessel names either so I’m guessing that they’re using the frequency illegally.
UPDATE!
I’ve been reliably informed that there is a frequency overlap between the marine band Channel 83 & a local comms repeater here in Stockport.I find the fact that Ofcom have allowed a frequency overlap here a little odd, since the marine band is used on the inland waterways, although not as much as coastal marine locations.
Here’s the final instalment of the new high gain TV antenna & it’s masthead amplifier.
High Gain Antenna
Here’s the new antenna on it’s removable mast. This apparently will give 13db of gain over the old antenna. The masthead amplifier box is mounted just below.
Amplifier
Here’s the amplifier just below the antenna. I do hope the seals on this hold against the weather! The amplifier inside isn’t protected at all.
Amplifier Module
Here’s the module itself. This is powered by +12v injected into the coax with the power supply I previously modified. F-type connectors are used. (I don’t like these connector types, their lack of a true centre pin is poor design in my opinion).
Here’s the power supply, mounted behind the TV where the cable comes through the hull.
PSUAmplifier PCB
Here’s the inside of the amplifier module. It’s very simple, with some input filtering to block out 4G mobile signals, and a single amplifier transistor.
I think the headline speaks for itself… The usual group, with their Baofengs… Grossly over on the power!
After this, they then went up to 446.070MHz, which is in the guard band between channels. All the while admitting they’re using massive high gain antennas as well.
Shortly after, they went over to 446.065MHz, still between the channels, but it’s close enough to have splatter all over the place. So in trying to get on a frequency that can’t easily be heard on PMR (in their opinion), all that they’ve accomplished is interfering with two separate channels at the same time! Here’s the aftermath of their channel switching on 446.065MHz.
One bit of my equipment that I’ve never looked into is my scanner, a handheld Uniden unit. I got this when Maplin Electronics had them on special offer a few years ago.
Uniden Scanner
Here’s the scanner itself, roughly the same size as a usual HT.
Back Cover Removed
Here the back cover has been removed, and the main RF board is visible at the top of the stack. Unfortunately the shielding cans are soldered on this unit, so no looking under there 🙁
On the right hand side of the board next to the antenna input is the main RF filter network, and it’s associated switching. The RF front end is under the shield closest to the front edge.
Controls & 3.3v Regulator
On the other side of the PCB is the Volume & Squelch potentiometers, along with a dedicated 3.3v switching supply. An NJM2360A High Precision DC/DC converter IC controls this one. A 3.3v test point is visible next to the regulator.
RF Board Reverse
Here’s the backside of the RF board, some more interesting parts here. There’s a pair of NJM3404A Single Supply Dual Op-Amp ICs, and a TK10931V Dual AM/FM IF Discriminator IC. This is the one that does all the back-end radio functionality. The audio amplifier for the internal speaker & external headphone jack is also on this PCB, top left. A board-to-board interconnect links this radio board with the main control board underneath.
Control PCB Front
Here’s the front of the control PCB, nothing much to see here, just the LCD & membrane keypad contacts.
Control PCB Reverse
And here’s the reverse side of the control board. All the interesting bits are here. The main microcontroller is on the right, a Renesas M38D59GF, a fairly powerful MCU, with onboard LCD drive, A/D converter, serial interface, 60K of ROM & 2K of RAM. It’s 6.143MHz clock crystal is just below it.
The mating connector for the RF board is in the centre here.
There is also a Microchip 24LC168 16KB I²C EEPROM next to the main microcontroller. This is probably for storing user settings, frequencies, etc.
EEPROM
The rest of this board is dedicated to battery charging and power supply, in the centre is a dual switching controller, I can’t figure out the numbers on the tiny SOT23 components in here, but this is dealing with the DC 6v input & to the left of that is the circuitry for charging the NiMH cells included with the scanner.
PSU
The last bit of this PCB is a BU2092FV Serial In / Parallel Out 4 channel driver. Not sure what this one is doing, it might be doing some signal multiplexing for the RF board interface. Unfortunately the tracks from this IC are routed on the inner layers of the board so they can’t be traced out.
I’ve always found programming repeaters into the UV-5R manually a bit of an arse, especially since the manual is pretty poor & very concise. Ringway Manchester have done a very good video detailing a simple way to get this done without a computer & most importantly, without any headaches!
Here’s some audio from last night on PMR, the regular group seem to be getting a little hacked off 🙂
(I do love the way these guys go on about abuse on the band when they’re transmitting on enough power to rival the BBC, they mustn’t know that PMR446 is limited to 500mW, the Baofengs they’re using only go as low as 1W, usually more when measured).
Onboard the boat we have a small issue with a weak TV signal, and this coupled with a 60′ long run of coax is an issue. Due to the loss in the coax, we’ve lost most of the already weak signal.
To try & solve this issue, I’m fitting a masthead amplifier unit.
These amplifiers are fed power down the same coax that’s carrying the RF signal, and a special power supply is supplied with the amplifier for this. However it’s only 240v AC, no 12v version available.
Here’s the power supply unit, which fits into the coax between the TV & the antenna.
Amplifier Supply
Luckily the 240v supply is easily removable & here has been replaced with a 12v regulator.
New Supply
There’s not very much inside the shielding can, just a few filter capacitors & an RF choke on the DC feed, to keep the RF out of the power supply system.
The original cable is used, so the supply doesn’t even look like it’s been modified from the outside.
More to come on this when I get the amplifier installed along with the new coax run 🙂
I thought I’d detail the process I use to fit an N-Type connector to a coax cable, as I don’t usually solder these connectors.
Backnut & Seal
Before stripping, fit the backnut, washer & rubber seal onto the cable.
Stripped Coax
The cable is first stripped back to reveal the shield. This cable has a foil tape as well as the usual copper braid.
Shield Connection
Once the inner core has been revealed, the shield washer is fitted. This has a knife edge on the inner diameter, to fit between the outer sheath & the shield, this makes the electrical connection.
Inner Insulation
With the shield washer fitted, the inner insulation can be cut back, it should be just about level with the final washer when you’re done, this allows the connector to fit together properly.
Center Core Trimmed
Trim the center conductor to about double the length required, to allow it to be folded over, as shown. This allows the copper to spring back against the center pin of the connector when it’s fitted, to allow a good connection.
Final Washer
Here the final washer is fitted over the shield washer. The center insulation should be at the same level to allow the center pin to fit properly.
Center Terminal
Finally, the center pin is pushed over the inner conductor of the cable, with it’s insulating spacer. Soldering these usually results in the plastic melting and a ruined connector.
Finished Plug
Finished plug. Make sure the backnut is tightened fully home, without twisting the connector body itself. After I’m done with the termination, I use self-amalgamating tape to form a strain relief on the cable. This prevents it from breaking at the point where it enters the backnut.
I’ve been terminating these connectors this way for a long time & have not had any issues with SWR or bad connections, dispite the fact that I don’t solder them. This also has the advantage that fewer tools are required for the job & the connectors can easily be reused should the cable wear out.
Here’s a rather unique device for protecting safes & vaults from attack by thefts.
It’s an Aritech VV602 seismic detector, based on piezoelectric sensors. Not surprisingly, this unit is covered in tamper sensors as well. There are several different sensor types in use:
Piezoelectric vibration sensing
Thermal sensing
Magnetic sensing
Manual Tamper Switches
Sensor Unit
Above is the main unit, with the thermal sensor. This is just a thermal fuse, very commonly used in everything from room heaters to hairdryers. This one triggers at 84°C. The adjustment pot is also visible here.
Mounting Plate
Above is the magnetic mounting plate used to attach the device to the safe. These units are apparently mounted over the keyhole of the safe to protect the lock, so they need to be easily removable to access the safe. This is a very strong magnet & it isn’t possible to pull it from a metal object without triggering the sensor.
Piezo Sensor
Above is the piezo vibration sensor, bonded to the backplate. When the unit receives vibration or shock, this transducer generates a voltage, which is fed to the control logic below.
Control Logic
Here’s the reverse of the main PCB with the control logic ICs. These are basic logic gates, with a couple of comparators. One of the tamper switches is in the bottom left corner.
Main PCB
Main PCB with the connection terminals. Another tamper switch is in the top left corner, the solid-state relay is under the shield, next to the magnetic tamper switch. (Reed switch).
Some adjustment is provided for sensitivity. I’ve not found much of a difference in sensitivity though when it’s set to different levels.
Reed Tamper
Magnetic reed switch tamper on the right. Main output solid-state relay on the left under the shield.
This unit was given to me after it apparently went faulty. But on applying power it seems to work fine. Must be those experts again 😉
As per my site update post, I have migrated my radio log onto a new system, from CQRLOG.
CQR log has served me well since I first started in Amateur Radio, however it’s a bit complex to use, requires a backend MySQL server for it’s database, and as it’s a local application, it’s not possible to share my log with other Hams without some difficulty.
The only other major system with an online logging system is QRZ, and I find that particular site a bit of a pain, and many of the features there aren’t free. (Although it’s not horrendously expensive, I’m on a very tight budget & I must save where I can).
CQRLOG Screenshot
Because of these points, I went on a search for something that would better serve my needs. I have discovered during this search that there’s liitle out there in the self-hosted respect.
I did however find Cloudlog, a web based logging system in PHP & MySQL.
This new system allows integration with the main site, as I can run it on the same server & LAMP stack, it’s very simple to use, is visually pleasing and it even generates a Google Map view of recent QSO locations.
It will also allow me to save some resources on my main PC, running a full-blown MySQL server in the background just for a single application is resource intensive, and a bit of a waste of CPU cycles. (CQRLOG and it’s associated MySQL server is 300MB of disk space, CloudLog is 27MB).
Backups are made simpler with this system also, as it’s running on my core systems, incremental backups are taken every 3 hours, with a full system backup every 24 hours. Combined with offsite backup sync, data loss is very unlikely in any event. All this is completely automatic.
I can also take an ADIF file from Cloudlog for use with any other logging application, if the need arises.
Cloudlog is built & maintained by Peter Goodhall, 2E0SQL.
From the looks of Github, there’s also a version 2 in development, although now I have version 1 up & running, I might just stick with it, unless an easy upgrade path is available.
When I am not operating mobile, new QSOs should appear in this system almost immediately, with their respective pins on the map. (These are generated by the Grid Square location, so accuracy may vary).
If you’ve spoken to me on the air & I haven’t updated it, I’m most likely away from an internet connection, in which case your callsign will appear as soon as I have access.
After a few years of running with the same look, I’ve decided on some changes.
New theme!
The site now looks much better, and has better support for more eye candy 😉
Addition of my QRZ link
New QSO logging system
Accessible from a button in the header, this is my new preferred system for logging my radio contacts. (I was originally using CQRLOG under Linux). If I’ve spoken to you on the radio your callsign will most likely appear immediately. 🙂
If not, I’m probably working mobile. In that case, drop me a comment or an E-Mail 🙂
Finally there have been some behind the scenes changes to implement some better security on site.
Getting the number of hits I do per day, this site gets attacked by the Internet’s Great Unwashed on a regular basis. No attack has ever been successful but more security never hurts!
Here’s a quick look at a Sainsmart frequency counter module. These are useful little gadgets, showing the locked frequency on a small LCD display.
It’s built around an ATMega328 microcontroller (µC), and an MB501L Prescaler IC. The circuit for this is very simple, and is easily traced out from the board.
Frequency Counter
Here’s the back of the board, with the µC on the left & the prescaler IC on the right. This uses a rather novel method for calibration, which is the trimmer capacitor next to the crystal. This trimmer varies the frequency of the µC’s oscillator, affecting the calibration.
Input protection is provided by a pair of 1N4148 diodes in inverse parallel. These will clamp the input to +/-1v.
The prescaler IC is set to 1/64 divide ratio. This means that for an input frequency of 433MHz, it will output a frequency of 6.765625MHz to the µC.
The software in the µC will then calculate the input frequency from this intermediate frequency. This is done because the ATMega controllers aren’t very cabable of measuring such high frequencies.
The calculated frequency is then displayed on the LCD. This is a standard HD44780 display module.
LCD
Power is provided by a 9v PP3 battery, which is then regulated down by a standard LM7805 linear regulator.
Readout
I’ve found it’s not very accurate at all at the lower frequencies, when I fed it 40MHz from a signal generator it displayed a frequency of around 74MHz. This is probably due to the prescaler & the software not being configured for such a low input. In the case for 40MHz input the scaled frequency would have been 625kHz.
After watching a video over at Scullcom Hobby Electronics on YouTube, I figured I’d build one of these precision references to calibrate my multimeters.
It’s based around a REF102P 10v precision reference & an INA105P precision unity gain differential amplifier.
For full information, check out the video, I won’t go into the details here, just my particular circuit & PCB layout.
In the video, Veroboard is used. I’m not too fond of the stuff personally. I find it far too easy to make mistakes & it never quite looks good enough. To this end I have spun a board in Eagle, as usual.
Precision Ref SCH – Click to Embiggen
Here’s the schematic layout, the same as is in the video.
Precision Ref BRD
As usual, the Eagle CAD layout files can be found at the bottom of the post.
And the associated PCB layout. I have added the option to be able to tweak the output, to get a more accurate calibration, which can be added by connecting JP1 on the PCB.
As in the original build, this unit uses pre-built DC-DC converter & Li-Ion charger modules. A handy Eagle library can be found online for these parts.
I have however left off the battery monitor section of the circuit, since I plan to use a protected lithium cell for power. This also allowed me to keep the board size down, & use a single sided layout.
Toner Transfer Paper
Here’s the track layout ready to iron onto the copper clad board. I use the popular toner transfer system with special paper from eBay, this stuff has a coating that allows the toner to easily be transferred to the PCB without having to mess about with soaking in water & scraping paper off.
Ironed On
Here’s the paper having just been ironed onto the copper. After waiting for the board to cool off the paper is peeled off, leaving just the toner on the PCB.
Etched PCB
PCB just out of the etch tank, drilled & with the solder pins for the modules installed. Only one issue with the transfer, in the bottom left corner of the board is visible, a very small section of copper was over etched.
This is easily fixed with a small piece of wire.
Components Populated
Main components populated. The DC-DC converter is set at 24v output, which the linear regulator then drops down to the +15v rail for the reference IC. The linear section of the regulator, along with the LC filter on the output of the switching regulator produce a low-ripple supply.
SMPS Ripple
Here’s the scope reading the AC ripple on the output of the DC-DC converter. Scale is 100mV/Div. Roughly 150mV of ripple is riding on top of the DC rail.
Linear PSU Ripple
And here’s the output from the linear regulator, scale of 50mV/Div. Ripple has been reduced to ~15mV for the reference IC.
In total the circuit as built has a power consumption of ~0.5W, most of which is being dissipated as heat in the linear part of the PSU.
Here’s another viewfinder CRT, removed from a 1980’s vintage VHS camera I managed to get cheap from eBay.
This unit is very similar to the last one I posted about, although there are a few small differences in the control circuitry.
Viewfinder Schematic – Click to Embiggen
Here’s the schematic, showing all the functional blocks of the viewfinder circuitry. An integrated viewfinder IC is used, which generates all the required scan waveforms for the CRT.
On the left is the input connector, with the power & video signals. Only pins 2 (GND), 3 (Composite video), & 4 (+8v) are needed here. Pin 1 outputs a horizontal sync signal for use elsewhere in the camera, while pin 5 fed the recording indicator LED.
To make connection easier, I have rearranged the wires in the input connector to a more understandable colour scheme:
Input Connector
Red & Blue for power input, & a coax for the video. For the video GND connection, I have repurposed the Rec. LED input pin, putting a shorting link across where the LED would go to create a link to signal ground. Keeping this separate from the power GND connection reduces noise on the CRT.
Viewfinder CRT Assembly
Here’s the complete assembly liberated from it’s plastic enclosure.
PCB Closeup
Closeup of the control PCB. The 3 potentiometers control the CRT brightness, focus & vertical size.
M01KGG007WB CRT
The tiny CRT. Only ~60mm in length, with an 18mm screen size. This tube runs on +2294v final anode voltage. Much higher than I expected.
Electron Gun Closeup
The electron gun assembly, with the cathode, focus & final anode cups.
Phosphor Screen
This screen is just a little bigger than a UK 5p piece! A marvel of precision engineering.
Here’s another active balancing circuit for large ultracapacitor banks, this one is designed for a series string of 6, at 2.5v per capacitor.
Based on the design here, I have transcribed the circuit into Eagle & designed a PCB layout.
Ultracap Balancer Circuit – Click to Embiggen
As can be seen from the circuit diagram above, this is just 6 copies of the circuit from the above link, with screw terminals to attach to the capacitor string.
Ultracap Balancer PCB
And here’s the PCB. the MOSFETs & OpAmps are very small SMT parts, so require a steady hand in soldering. This board can easily be etched by hand as there’s only 3 links on the top side. No need for a double sided PCB.
As always, the Eagle project files & my Eagle library collection are available below:
I recently managed to score a 3″ B&W portable TV on eBay, a Panasonic TR-3000G. As these old units are now useless, thanks to the switch off of analogue TV signalling, I figured I could find a composite signal internally & drive the CRT with an external source.
Panasonic TR-3000G
Here’s the TV in it’s native state. Running from 9v DC, or 6 D size cells. I’m guessing from somewhere around the 1970’s. Here is the CRT & associated drive circuitry, removed from the casing:
CRT Module
After dissecting the loom wiring between the CRT board & the RF/tuner board, I figured out I had to short out Pins 1,2 & 5 on the H header to get the CRT to operate straight from the power switch. This board also generates the required voltages & signals to drive the RF tuner section. I have removed the loom from this, as the PCB operates fine without. It doesn’t seem to be fussy about power input either: it’s specified at 9v, but seems to operate fine between 7.5v & 14.5v DC without issue.
Video Connections
Tracing the wiring from the tuner PCB revealed a length of coax snaking off to the section marked Video/Sync. I successfully found the composite input!
Running OSMC
A quick bit of wiring to a Raspberry Pi, & we have stable video! For such an old unit, the picture quality is brilliant, very sharp focus.
Matsushita 85VB4 CRT
Closeup of the CRT itself. I haven’t been able to find much data on this unit, but I’m guessing it’s similar to many commercial viewfinder CRTs.
Electron Gun Closeup
Amazingly, there isn’t a single IC in the video circuitry, it’s all discrete components. This probably accounts for the large overall size of the control PCB. Viewfinder CRTs from a few years later on are usually driven with a single IC & a few passives that provide all the same functions.
I’ve been doing some tinkering with the RN-52 Bluetooth Audio module from Roving Networks, in prep for building a portable wireless speaker system, & thought I’d share my designs.
Initially I was having some issues with RF noise on the audio output from the RN-52, as I was only using the outputs single-ended. The module didn’t like this treatment, with all the RF whine coming straight out of the speakers.
To fix this issue I have used a pair of jellybean LM386 audio power amplifiers, running in differential input mode. This solves the high-pitched whine when the audio is enabled, & also allows the module to directly drive a set of 32Ω headphones at a reasonable level.
In Eagle I have designed a simple board, routing only the audio output, serial TTL & command mode pins out, along with the supporting power supply circuitry to operate from 12v DC.
RN-52 Breadboard
Above is the current incarnation of the circuit on the breadboard. The RN-52 is on the left, audio power stage in the centre & headphone output on the right.
RN-52 Breakout
The bluetooth module on a breakout board. I was cheap in this case & etched my own board. I’m not paying Sparkfun, (as much as I like them), an extra ~£10 for a small PCB with the pins broken out. Much cheaper to spend 15 minutes with the laser printer & the iron, & do a toner transfer PCB.
As this board is single sided, I added a ground plane on the underside with copper foil, to help with the RF issues. Breadboards really aren’t all that good at rejecting noise induced when there’s a 2.4GHz transceiver mounted on them.
LM386 Amplifier
The LM386 audio power stage. The differential inputs from the module are capacitively coupled with 1µF electrolytics. This setup remarkably reduced the noise on the output. I left these at their default gain of 20, as I’ll be connecting another high power amplifier stage to drive large speakers.
RN-52 Eagle Layout
Here’s the circuit laid out in Eagle, ready for PCB.
RN-52 Eagle PCB
And here’s the PCB layout. Only one link required for the +5v line from the TTL serial port.
As always, the Eagle PCB & Schematic layout files are available at the bottom of the article.
*Update 29-01-15*
Rerouted a few things:
Moved the audio power stage to the +12v rail to improve sound response. – As the LM386 has a max input voltage of 12v (absolute maximum 15v), a regulated supply is recommended. The LM386-N4 variant has a higher voltage range, up to 18v. This should be suitable for an unregulated supply.
Removed 1µF coupling capacitors to reduce distortion & amplifier hiss. The capacitors appeared to cause some instability on the amplifier, causing random distortion. Removing them has cured this. No signal hiss has also been reduced to a very low level.
Reversed input polarity on input of one of the amplifiers – this appears to produce better audio.
Added PWR.EN header to allow connection of power button. Saves hassle of cycling power to the board when the RN-52 goes into sleep mode.
It’s official. I’m now part of the uRadMonitor network, & assisting in some of the current issues with networking some people (including myself) have been having.
It seems that the uRadMonitor isn’t sending out technically-valid DHCP requests, here is what Wireshark thinks of the DHCP on my production network hardware setup:
WireShark Screencap
As can be seen, the monitor unit is sending a DHCP request of 319 bytes, where a standard length DHCP Request packet should be ~324 bytes, as can be seen on the below screen capture.
Valid DHCP
This valid one was generated from the same SPI Ethernet module as the monitor, (Microchip ENC28J60) connected to an Arduino. Standard example code from the EtherCard library was used to set up the DHCP. The MAC address of the monitor was also cloned to this setup to rule out the possibility of that being the root cause.
My deductive reasoning in this case points to the firmware on the monitor being at fault, rather than the SPI ethernet hardware, or my network hardware. Radu over at uRadMonitor is looking into the firmware being at fault.
Strangely, most routers don’t seem to have an issue with the monitor, as connecting another router on a separate subnet works fine, and Wireshark doesn’t even complain about an invalid DHCP packet, although it’s exactly the same.
Working DHCP
As the firmware for the devices isn’t currently available for me to pick apart & see if I can find the fault, it’s up to Radu to get this fixed at the moment.
Now, for a µTeardown:
uRadMonitor
Here is the monitor, a small aluminium box, with power & network.
PCB
Removing 4 screws in the end plate reveals the PCB, with the Geiger-Mueller tube along the top edge. My personal serial number is also on the PCB.
The ethernet module is on the right, with the DC barrel jack.
PCB Bottom
Here is the bottom of the PCB, with the control MCU & the tiny high voltage inverter for the Geiger tube.
Control Electronics
A Closeup of the main MCU, an ATMega328p
Logo
PCB Logo. Very artsy 😉
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