DPS5005, now with comms

It’s exciting to see the continued development of the DPS5005 and ‘3005. Today Rd Tech released a version with USB/Bluetooth connectivity and I just ordered one to make sure OpenDPS runs on it. The new version seems be fitted with a JST connector which makes connecting an ESP8266 a bit easier. It also has different MOSFETs by the looks of it.

Now I only need to wait 25-36 days for shipping. Oh, and in case you wonder. I am not affiliated with Rd Tech.

Hacking the DPS5005

Some time ago I found the DPS5005 while browsing AliExpress for programmable power supplies. To be honest, I dismissed the ‘5005 since it was not a complete product. Then HAD wrote about it in december last year and after watching YouTube user @iforce2d’s video I just had to get one. The overall impression was quite good but the software was a bit cluttered and the DPS5005 could not be instrumented via a serial port (or wifi). Looking closely at the sandwich PCB design I noticed the DPS is powered by an STM32, which is pretty much what I expected. And so begun the OpenDPS project, a free firmware replacement for the DPS5005 and friends.

OpenDPS, wifi connected
OpenDPS, wifi connected

This write up of the OpenDPS project is divided into three parts. Part one (this one) covers reverse engineering the stock firmware and could be of interest for those looking at reverse engineering STM32 devices in general. Part two covers the design of OpenDPS, the name given to the open DPS5005 firmware. Part three covers the upgrade process of stock DPS:es and connecting these to the world. If you only want to upgrade your DPS you may skip directly to part three.

Reverse engineering the DPS5005

The reverse engineering of the DPS5005 can be summarised as “bring up of the STM32 based DPS5005 hardware and writing an application for it”. This is pretty much my day job but I always have the hardware schematics and the hardware design engineer at hand. This time, obviously, I had neither which was a bit more challenging. So where does one start? Looking at the PCB, I quickly found the serial port. That was a dud, completely silent. Fake port! I later realised the DPS5005 stock firmware does not even initialise the serial port. The STM32 is covered by the TFT display, which in turn is soldered using eight pins. As I did not have the time to play with iron and solder wick I resorted to a metal saw and promptly sawed the TFT display off (please note this is not the unit in the pictures below).

SWO pinout
Top: SWO pinout, UART below

Warranty voided, oh there actually was none to begin with. Having the STM32 in the open quickly allowed me to identify the five test points at the top of the PCB, the expected SWO trace port. But had the producers locked the SWO port when flashing the firmware? Luckily, no.

Debugger connected
Debugger connected

After some soldering, connecting an STLink clone and selecting an appropriate OpenOCD configuration for the STM32F100, I had a go at it:

Yay! Next I connected to OpenOCD to examine the target:

So “readout protection” is enabled which mean you cannot read the firmware from flash. Not a biggie as I was not interested in the stock firmware in itself, only what it controlled. So what would be needed to create the OpenDPS firmware?

  • Learn how buttons and other IOs are connected.
  • What STM32 peripheral drives what function?
  • Controlling the output voltage (controlled by the DAC?)
  • Current limiter (maybe ADC?)
  • Measuring input and output voltage (definitely ADC)
  • Dimmable TFT (not needed 🙂
  • Write a TFT driver

To assist, I created a Python script (ocd-client.py) connecting to OpenOCD for dumping various STM32 device registers. Eg, by dumping the entire DAC register area I could determine the DAC was in use. The buttons I could identify by dumping the GPIO input registers, pressing the button and dumping the registers again. The entire GPIO setup can be recreated by this script and I learned the output voltage really is driven by the DAC. The TFT backlight is driven by timer 4 and the output current, input voltage and output voltage are measured using ADC1 on channels 7, 8 and 9. The 1.44″ TFT is an ILI9163C and I used @SumoToy’s driver for this. The SPI select pin for the display is grounded which is a clever way of saving one pin for designs where there is only one device connected on the SPI bus. Additionally, the display does not use the MISO pin. The most important thing now was how to control the DAC to set a desired output voltage, how to interpret the ADC1 values measuring the output voltage, current draw and input voltage. Normally, one would look at the schematics to figure out what an ADC reading means but in this case I had to reverse engineer that. I simply connected a multimeter, tried a few settings on the stock firmware, observed the ADC1 reading and plotted the result. Next, I created a simple application using the lovely libopencm3 and tested in on a “Bluepill” before wiping the DPS5005. Telnetting to port 4444 again I tried:

Failed! Hmmm, let’s do a power cycle, restart OpenOCD and try that again.

Now that’s better! I am not sure why it fails the first time, it did so on both my units but succeeded on the second attempt. A simple ‘make flash’ and the display showed my test pattern and the power output was at the expected 5V. Mission, partly, accomplished! I could reflash the DPS5005 and control the voltage setting. Time to write a proper application. More in part two.

OpenDPS Design

This is the second part about hacking the DPS5005. Part one covers the reverse engineering of the DPS5005 and part three covers the process of upgrading stock DPS5005:s to OpenDPS.

 

The goal of OpenDPS is to reflash the stock DPS5005 (and friends) with a firmware that has the same functionality, has a less cluttered user interface and is remote controllable via wifi or a serial port. The application needs to respond to user input both via buttons and the serial port and also via ADC readings telling us if the current draw is larger than what we allowed. Buttons and UART RX are handled using interrupts and obviously the ADC needs to be interrupt based too for fast response (and less smoke). Responding to user input and TFT drawing can be left to the application context.

System Overview

The following modules are used in OpenDPS:

  • event – uses a ring buffer for storing events from the interrupt context to be handled in the application context. Events are button presses, received bytes on the UART and over current protection triggers
  • hw – the hardware abstraction (ADC, GPIO, …)
  • ili9631c – the TFT driver
  • opendps – main application
  • past – for storing persistent parameters in flash
  • protocol – helper for the serial protocol to instrument the OpenDPS device
  • pwrctl – power control, the DAC and calculations to convert ADC readings to eg. current draw
  • ringbuf – a ringbuffer implementation
  • spi_driver – just that
  • tft – TFT utility functions
  • tick systick handler with 1ms resolution
  • uframe – framing of serial protocol spoken
  • ui – handle the user interface

Control Flow

The application in opendps.c sits in a busy loop waiting for events to arrive in the circular buffer. Button presses, serial RX and over current protection events are placed in this buffer. The application calls the UI module that updates the UI with fresh measurements every 250ms. User input is also handled in the UI module. Events are 16 bit integers encoding the event type and optional event data. For the UART RX event the data obviously is the received byte. For button presses we also include information telling us if the press was a long press.

ADC and DAC Management

As I did not have the schematics at hand I had to reverse engineer the formula to calculate voltage/current based on ADC readings. I did some measurements and plotted in a Google Docs spreadsheet to find out

  • V_in(ADC1_IN8) – given a reading on channel 8, what is the input voltage?
  • V_out(ADC1_IN9) – given a reading on channel 9, what is the output voltage?
  • V_out(DAC) – what is the output voltage given a DAC setting? (and the inverse)
  • I_out(ADC1_IN7) – given a reading on channel 7, what is the current draw? (and the inverse)

To reduce complexity in the ADC IRQ handler, I pre calculate the ADC value that corresponds to the dialled current limit to quickly determine if we went over the limit. Here I ran into some issues as the ADC reading of the current draw differed between the two ‘5005s I had at hand. One of the units reported the wrong current draw which was tracked down to a different value when no current was drawn at all. The remedy is to take the first 1000 samples at system startup to calculate the ADC value for 0.00mA current draw and compensate in the calculations (see adc_i_offset & friends in hw.c)

Additionally, I currently collect a number of “over current samples” before triggering the OCP. This scheme needs some investigation.

Persistent Storage

User settings need to be persisted and this is taken care of by the past (parameter storage) module. This module uses two blocks for storing data. One is the “current block” and when it gets full a garbage collection is performed and the data is copied to the other block. Counters tell which block is the most recent one. In theory, power loss should not lead to corruption and/or data loss.

Graphics

An anti aliased rendering of Ubuntu Condensed is used in two different sizes for the UI. The font is found in gfx/fonts and consists of two files. The glyphs itself (eg. ubuntu_condensed_48.png) and one image describing the widths of each character (eg. ubuntu_condensed_48_width.png).

Ubuntu Condensed, 48
Ubuntu Condensed, 48

The widths are indicated by a white pixel in the first row:

Width markings
Width markings

The fonts are converted by ‘make fonts’ which invokes font-convert.py. The glyph PNG is converted to BGR565 (used by the TFT) and written to font-X.[h|c]. Each glyph is converted to a separate blob which speeds up blitting to the TFT. See tft_putch(…) in tft.c for usage. Blocking DMA is used to transfer the glyph data. One enhancement would be to have a list of DMA descriptors and fire the next DMA job in ISR context at the completion of the previous one. The icons displayed are handled in a similar manner (see eg. wifi.h) and are converted by ‘make graphics’. You should be able to change the font with little difficulty, in theory 🙂

Remote Control

The OpenDPS device can be controlled via the UART port and you can either connect an FTDI adapter or an ESP8266. The latter is the most fun. A simple serial protocol is used (see protocol.h and uframe.h). Either way you go, there is a Python script to talk to the OpenDPS device, dpsctl.py:

The utility is agnostic as to how the OpenDPS device is connected. Provide an ip address and it will attempt to talk to that. Provide a TTY device and it will attempt to talk to that. For wifi connected DPS:es, you can provide the option –scan to find all OpenDPS devices on your network.

Any good old ESP8266 board with the UART exposed will work. Connect GND, RX and TX, build and flash esp8266-proxy (don’t forget to set your wifi credentials) and you should be good to go.

Note that you currently cannot use the master branch on the main ESP Open RTOS repository as my PR for a function needed for multicast has not been merged yet.

The design of esp8266-proxy is quite minimalistic. It receives UDP packets on port 5005, sends the content on the serial port and returns the answer to the UDP source address and port.

When OpenDPS starts the wifi icon is flashing at 1Hz. When it goes steady your ESP8266 has connected to your wifi and told the OpenDPS that it is connected. Try scanning for it:

Next try pinging it:

The TFT should flash once as a visual indication. If you get ‘Error: timeout talking to device 172.16.3.203’, check if you swapped RX and TX. You can always connect an FTDI adapter on either RX pin on the ESP8266 and OpenDPS to debug the communication.

That concludes part two, please see part three for a description of how to upgrade your DPS5005 to an OpenDPS 5005.

Upgrading your DPS5005

This is the third article about hacking the DPS5005. Part one covers the reverse engineering of the DPS5005 and part two covers the design of OpenDPS.

April 14th 2017 update: is has been verified that OpenDPS can push 5A. Thanks @johannes!

June 9th 2017 update: added a note on saving the STM32 peripheral settings before wiping the internal flash.

Although this guide is written for the ‘5005 it should work for the entire DPS family but I only have 5005s to test with. Before we begin I should mention that the stock firmware will be gone permanently. As readout protection is enabled on the STM32, the FW cannot be extracted and I have no source for it. Additionally, I take no responsibility if you destroy your DPS. That said, let the fun begin. You will need a DPS5005 (or similar), an STLink clone and some wire. Either you solder the wire onto the DPS or you can use female-male dupont wires for flashing.

Teardown

First you need to remove the PCB from the (semi) housing. Use a small flat screwdriver to prey the PCB loose from the retaining flaps.

Teardown
Teardown

Be careful not to break the retaining flaps (not that they’re fragile, but still). They are very much needed for holding the front panel in place when you press the buttons.

Solder some AWG26 wire onto the SWO and UART ports. It is advisable not to solder pin headers as there is limited room inside the housing. I added dupont jumper housings at the end of the cables to aid in connecting them to the STLink clone and FTDI ditto. Hint: make the cables “strech” backwards, from the display.

SWO/UART pinout
Top: SWO, lower: UART

If you do not want to solder (and do not want any remote control) (and have steady hands) you could connect three female-male dupont cables to the STLink clone and hold them pressed against the DPS while flashing.

Debugger connected, UART cable at the top
Debugger connected, UART cable at the top

Building OpenDPS

With that in place you should install OpenOCD and an ARM GCC toolchain. For GCC, Launchpad is a good place to start. For OpenOCD, YMMW. If you are on macOS you can find OpenOCD here (it installs as /Applications/GNU ARM Eclipse/OpenOCD/0.10.0-201610281609-dev/bin/openocd). With the tools in place you’re ready for the next step.

Flashing

Next you need to unlock the internal flash of the STM32 before flashing (which causes a complete erase). Start OpenOCD:

You will receive a few lines of output ending with “Info : stm32f1x.cpu: hardware has 6 breakpoints, 4 watchpoints” if the connection was successful.

Please note! Before you unlock and erase the STM32 flash, you should make a dump of the STM32 peripheral settings of your stock DPS firmware. The DPS hardware might change at any time and if you flash OpenDPS and it does not work because eg. the GPIO pin enabling output power was changed, things get difficult. The ocd-client.py script will assist you now that OpenOCD is running. Please note that OpenOCD might interfere with the stock firmware. When you connect, the stock FW might lock up. First, power on the DPS and make sure the power output is disabled but set to e.g. 5V, start OpenOCD and type:

If needed, restart the unit (and OpenOCD), enable power output @ 5V and type:

Rinse and repeat for one or two more voltage levels. Check the log files, there should be no lines saying “Parsing error”. If your OpenDPS does not work, these files will enable me (or someone else, remember this is open source you 😀 ) to pinpoint the problem.

Now let’s wipe that flash. In another terminal:

and type:

You will probably get the following, ending with an error:

Keep calm. Restart OpenOCD, toggle power on the DPS and try again. This time you should see:

Time to flash:

The last two lines should read:

and your DPS5005 is now an OpenDPS 5005.

OpenDPS
OpenDPS, now with wifi

Congratulations! If things went south somwhere, feel free to ask for help in the comments below.

From here you can use the OpenDPS as a stand alone device, control it via a serial port or control it via wifi by connecting an ESP8266.

Short User Manual

When you power on your OpenDPS, the current voltage and current limit settings are displayed and the power output is always disabled. Pressing ON/OFF will enable power output and the display will now show the measured output voltage and the measured current draw. If the screen flashes once and goes back to displaying the voltage/current settings, the over current protection kicked in. Press ON/OFF again to disable the power output.

Press the SET button to go into editing mode. Press the V and A buttons to move between the voltage and current settings. Press the rotary knob to step sideways and turn the knob to change the values. Press SET again to exit editing mode.

Press and hold the knob for two seconds to lock the keys, long press again to unlock. A long press of the SET key will invert the display.

When your OpenDPS starts it will wait for a wifi connection from a connected ESP8266 and the wifi icon will flash at 1Hz. If it does not get a wifi connection, the wifi icon will be turned off after 10 seconds. If there was an error connecting to your wifi network, the wifi icon will flash at 4Hz.

Remote Serial Control

If you soldered wires to the UART port, connect an FTDI adapter and try the dpsctl.py tool:

The TFT should flash once as a visual indication. If you get ‘Error: timeout talking to device’, check if you swapped RX and TX and/or forgot to connect GND.

The port setting can be set in an environment variable

After setting the DPSIF variable, you can try setting the output voltage to 3.3V:

enable the output:

check the measurements:

If serial control is what you aimed for, you can get rid of the annoying flashing wifi icon by adding WIFI=0 when building OpenDPS

Remote Wifi Control

For wifi control, any good old ESP8266 board with the UART exposed will work. Connect GND, RX and TX, build and flash esp8266-proxy (don’t forget to set your wifi credentials) and you should be good to go.

Note that you currently cannot use the master branch on the main ESP Open RTOS repository as my PR for a function needed for multicast has not been merged yet.

When your OpenDPS has connected to your wifi network, try the ‘scan’ command to find out its IP number:

Next try pinging it:

The TFT should flash once as a visual indication. If you get ‘Error: timeout talking to device 172.16.3.203’, check if you swapped RX and TX. The dpsctl.py tool has the same functionality over wifi as well as the serial port.

Sadly, you cannot power your ESP8266 from your OpenDPS. The VDD pin next to the SWO port is connected to U4 (under the TFT), an MD7133H 3.3V regulator which only provides a measly 30mA (yes, thirty). Additionally, this regulator is powered by U3 (on the backside, next to the screw terminal) which is an XL7005A supplying 400mA @ 5V which could be a bit over the edge for a power hungry, cold booting ESP8266.

 

Todos

There are a few todos in the code but overall OpenDPS should be stable for everyday use.


That’s it, have fun hacking your DPS5005!

 

Goodbye ESP3212

Sometimes you bet on the wrong horse. I put my money down on the ESP3212 as I had seen the images of sample modules and AiThinker seemed to be on the way to mass produce this lovely little thing. As I had a bunch of designs to send off to Dirty PCBs, I quickly whipped up an ESP3212 version of my Esparducam board. The day after the boards went into production (early november IIRC) I read that the ESP3212 was scrapped in favour of the ESP32S. Not a completely bad choice as the 3212 was not pin compatible with Espressifs version of the module. But still.

ESP3212 coaster :)
ESP3212 coaster 🙂

So, if you actually managed to get your hands on a ‘3212 and wish to test it on this board I’d be happy to send one to you for the price of p & p. Goodbye ESP3212, I hardly ever knew you.

The Commadorable 64

Update Aug 28th: The BOM for all variants is now on Github. Please see the notes at the end if you want to build a Commadorable 64 yourself.

The ILI9341 based QVGA displays found on eBay for €4 are well suited for making small screenlets telling the current temperature, weather forecasts, traffic situation to work and spreading them over the house. As PCB design is both fun, cheap and rewarding I did a custom PCB for these tiny displays. Actually, I made three, one for each of the 2.2″, 2.4″ and 2.8″ screens. The 2.8″ version has not been produced but the smaller variant have and work well. From 2.4″ and onwards there is (untested) touch support on the screen modules.

The “Hello World” application for this project also named the PCBs. I call them Commadorable 64. Here is why:

LEGO Stormtrooper added for size reference
LEGO Stormtrooper added for size reference

The cursor blinks but I resisted the urge to create an animated GIF. “Commadorable 64” is a play with “Commodore 64” and “adorable”. It has been scientifically proven that those for whom the Commodore 64 played a significant part of their childhood will look at the 2.2″ version of the C64 start screen and react the same way as cat people looking at kittens. Heads will be tilted slightly sideways, smiles appear and sounds like “naaaaaaaw” will be heard. I have one of these at work and depending on childhood experiences people will either go “what?” or “naaaaaaw”.

ESP side
ESP side

The PCB is soldered directly to the pins of the ILI9341 module. Some of these screens will probably end up in other applications in the future. The other day I read about openframe.io and adding support for these would be fun.

The PCBs can be ordered from DirtyPCBs.com, 2.2″ with a bonus AAduino and 2.4″ version with touch. The BOM consists of the usual components for my ESP8266 designs. We have 0603 resistors and capacitors, a 3x6x2.5mm momentary push button [eBay] for displaying the IP address, a SOT23-3 P-mosfet to control the backlight, an LM1117 voltage regulator and a SOD-123FL schottky diode for reverse power protection and optional mini USB connectors. The PCB can be powered in three different ways depending on personal preference (well, four including the esprog interface). There are footprints for normal [eBay] and vertical [eBay] mini USB connectors, depending on if the module is to stand on a table or hang from a wall (Eagle parts available on Github). In addition there is a 0.1″ header for power. All power paths are protected by the diode.

Further update Aug 28th. I see some 20+ orders on DirtyPCBs for both Commadorable 64 variants which is great fun and I would really love to hear what you will build. I have some recommendations you might find useful. I have received a few broken ESP-12e/f modules on eBay over time and one broken ILI9341 module. Because of that I always try the modules before soldering them using my Esparducam board with the ESP Pinlet add on board. When a module passes testing I flash it with the ESP Open RTOS OTA basic demo meaning I can OTA any device directly after soldering. Also, you will note there is no FTDI connector on these boards, the reason is described here. As UART output is still useful, I have one “development” variant with leads from an FTDI connector soldered to the GND/RXI/TXO esprog pads. Oh, and I also have one Commadorable 64 board with a female header for testing the ILI9341 modules before soldering them. If you have any questions about building the boards, sound off in the comments below.

Code and schematics on Github, as always.

Bridging ISM radio and wifi for lunch money

The ESP8266 has taken the maker community by storm and the hype is well deserved. Before the ESP we had the HopeRF ISM radio RFM12 and its successor RFM69. So is the ESP8266 an RFM69 killer? I would say no. Hell no even 🙂 The RFM69 is still very well suited for certain applications and the ESP8266 will not run for 2+ years on a set of AA batteries. The two can however play nicely together as a low cost ISM/wifi bridge. I did a custom PCB for this in the shape of a somewhat large USB stick, dubbed “Espism”.

 

Currently it works as an ISM sniffer posting the received packets on the MQTT topic espism-<macaddr>. Packets are posted in hex followed by the RSSI value:

A set of four LEDs indicate received packets. Well three LEDs as I made a mistake on the ground plane. The MQTT server IP and RFM69 network information is hard coded into the binary.

I ported Andreas Heßling’s STM32 RFM driver to the lovely ESP Open RTOS, my swiss army knife for ESP8266 development. The type-A right angle 90 degreee USB connector and 3x6x2.5mm push button can be found for little money on eBay. The push button currently serves no purpose but the plan is to perform a “master reset” of the device using this button. The rest of the BOM consists of 0603 resistors and capacitors, an LM1117 3.3V regulator and a SOT23 P-mosfet for driving the 0603 LEDs. Oh, and the ESP12F talking to an RFM69CW. The BOM should add up to about the price of lunch.

Code and schematics on Github as always.

Factory programming ESP8266 gadgets

The FTDI connector can be found on just about any ESP8266 design. If you are building a gadget to be deployed somewhere and not a full blown development board, the FTDI connector is somewhat overkill. And it is quite large. A few pins could be shaved off but we still have a through hole connector invading the other side of the PCB.

I ended up designing my own connector and it has been used sucessfully in all of my recent projects. The connector consists of five test points providing power, GND, TXO, RXI and GPIO0 for boot control. It takes very little single sided PCB space and is inspired by the TagConnect I use at work. Note that the power provided through the connector is unregulated.

I also designed a pogo pin connector to mate the test points and a small board with a DC barrel connector and the FTDI connector. This board has two switches for power and boot mode selection.

If you look carefully on the pogo pin adapter you see that the power pin is somewhat retracted. As the adapter will be hand held, the four other pins can be aligned to the device and with a gentle push power will be applied.

The pins used are P75-B1 1.02 mm (40 mil) [eBay] and the 9x4x8.5mm 3 way switches are also on eBay.

Schematics and my Eagle library with the device connector (“ESPROG-DEVICE”) as always on Github.

The AAduino

Update: you can now order the AAduino PCB from DirtyPCBs.com and get a Commadorable 64 bonus PCB for free.

I have been using Nathan Chantrell’s Tiny328 for quite some time as my swiss army knife ISM radio node. Now I wanted a more slim ISM node as my setup with a Tiny328 on a breadboard is not very “deployable”. I could of course 3D print a case for the Tiny328 but I have limited access to 3D printers and do not feel I have the time to explore that exciting part of the maker world just yet. This leaves me with finding off the shelf project boxes with a compartment for 2x AA batteries and the “radioduino” (and in an acceptable form factor). That search came up disappointingly, and surprisingly, short. I did have a set of standard eBay AA battery holders and looking at the 3x variant it occured to me. I needed to shrink the radio node, and the AAduino was born.

Honey, I shrunk the radioduino!

The AAduino is an wireless Arduino clone the size of an AA battery with Keystone battery terminals rotated 180° to act as positive and negative terminals. It is powered by an ATMega328p and is fitted with an RFM69C companion. There is room for two DS18B20 temperature sensors and an indicator LED.

I still think it looks a bit weird :)
I still think it looks a bit weird 🙂

It runs at 8Mhz to allow for greater life span since the CPU can run at a lower voltage. I have fused the 328 to brown out at 1.7V which is a bit out of spec at 8Mhz and slightly below what the RFM69C needs. Running at 4Mhz would be more suitable but I will see how well the node performs when the batteries are draining out.

AAduino, RFM69C side
AAduino, RFM69C side

Since the RFM69C is somewhat wider than an AA battery I used a file to make it slightly narrower. There is some room for that kind of modification without damaging the module. Update, the RFM69C will fit without modification. Next I clipped the legs of the DS18B20 until about 5mm remained and soldered it to the 3x pin header on the AAduino. I then drilled a hole in the battery box where the sensor can protrude and a small hole for the LED to shine through. The wire out of the battery box was cut, shorted and stuffed away inside the box.

AAduino inside 3xAA box
AAduino inside 3xAA box

I use battery terminals from Keystone available from RS Components, positive and negative. There seems to be a cheap eBay alternative but I have not tested those. The + and – markings on the PCB indicates (this is important, read carefully) the positive and negative poles of the battery we are pretending the AAduino is. The Keystone spring contact should be soldered to the + marking and the button contact to the – marking. There is no protection diode here so be careful. Also note! If you want to power the AAduino from a bench power supply, connect the power supply’s black negative lead to the + marking and the red positive lead to the – marking.

aaduino-v2

The 3xAA boxes are also from eBay and there seem to be two different types. One that is really good and one that is really crappy. I will let you in on the secret of buying the correct one. The good ones have a nice build quality and plastics and look like this. Note the rectangular piece of plastic below the battery compartment extending from side to side.

Good 3xAA holder
Good 3xAA holder

Looking at the crappy ones, well you can tell can’t you? In the top left corner it seems someone used a soldering iron on the poor thing. The lid does not snap in place very well and the plastics is really cheap.

Crappy 3xAA holder
Crappy 3xAA holder

Code, schematics and BOM on Github, as always.