Simple-Add-On Tester PCB

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In June 2023 I was chatting with a friend about my idea to lead a tour of the electronics scene in Shenzhen China and he suggested that we make and assemble a PCB as part of the tour. Since a bunch of us where attending the tour I thought it would be fun to hold a KiCad conference as well. We decided to hold it on the Makerfaire Sunday. As part of the conference I thought this would be the perfect time to do a workshop on assembling a small PCB. I thought it would be appropriate for attendees to assemble a small conference Simple-Add-On (SAO) hat that would plug into the conference badge.

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These are small-ish artistic PCB's that plug into some sort of conference badge to bling it up a bit. You can read more about the SAO 'standard' and it's history via these two links:

https://hackaday.io/project/175182-simple-add-ons-sao
https://hackaday.com/2019/03/20/introdu ... -standard/

Our conference started off being called: Shenzhen KiCon 2023 and later morphed into: KiCon Asia 2023: https://kicon.kicad.org/kicon-asia-2023/ I quickly whipped up the above simple PCB for the workshop. This had 5 components that included a reverse mounted red LED and a RGB SK6812-Mini-e LED. This LED has it's mounting pins laid out flat, so it allows you to fit the LED into a hole cut into the PCB, or as in our case you can push and fold the pins down onto the PCB pads and solder it into place. This means the light will shine up through the PCB. The other components are the SAO 6-pin connector, a 0603 resistor for the red LED and a 0603 100nF capacitor for the RGB LED.

The inaugural Asian KiCad Conference was a success. Some very interesting presentations and interesting people to talk too. It was great to hear from Wayne and Seth who flew over from America especially for the conference. We heard about upcoming features that are slated for version 8 and a few that might make it into version 9. We had talks on automating IC placement, AI routing, flipchips, laying out silicon and lots more. Exciting stuff!

The hands on SAO assembly workshop went well, with lots of fun had by all. Thanks to the volunteers who helped people through the process.

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What other SAO boards could I get designed up before I had to fly off to China?

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Since I was on a SAO Hat making mode, I thought I would have a go at making one for the Shenzhen based TroubleMaker makerspace and a koala for myself:

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I wanted the front side to be a clean as possible, so I used 0805 0 ohm resistors on the back side as track jumping resistors, this way I didn't need to place via's and tracks on the front side of the PCB. These two designs mostly used reverse mounted SK6812 (equivalent to the WS2812 LEDs). Note: these are designed to be powered from 5V with a 5V data signal, but I found that they *kind* of work with 3.3V power and data. I had enough SK6812 LEDs at home, but not enough for 100 boards, so the plan was to purchase more at the Shenzhen HQB electronic markets. It turned out that this was one LED I could not find at least with that part number. I did find an equivalent called: 6028RGB. These where even cheaper, so I purchased 500 of them to play with. I think they might use a GRB data sequence, vs the RGB data sequence used in the WS2812 RGB LEDs. But this all begs the question of how to test these SAO Hat boards?

Time for a SAO Tester PCB...

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I have now designed three SAO hat boards, so initially I designed my SAO Tester PCB with three SAO connectors. In the initial version of the Tester I had one socket configured with a MOSFET switchable power. I think that was so i could test the power side of things, but I never ended up using that functionality, so that was discarded in the next version. Having three SAO ports also meant the ESP32-C3 ran out of GPIO, so version two ended up with two SAO ports. This worked a treat, however once I started writing some example software for each SAO hat I realised that the Tester had no method of identifying what SAO Hat was plugged into a SAO Port.

I fixed that by adding a small SOT23-5 256 byte i2C based EEPROM to each SAO hat. I could then add and store some info and GPIO requirements in the EEPROM. As an aside, my initial code could not write to the EEPROM correctly, so much so that I thought that the batch of EEPROMs I had purchased from LCSC was faulty, so I quickly purchased a different one from a local vendor at the HQB market. When I had the same issue with that one too, I realised that it must be a problem with the library I was using. With some late night hacking, I fixed it that night hacking away in bed.

But this raised another issue that I hadn't thought through properly. When you have two SAO boards plugged into the Tester at the same time, there is no way to read the individual EEPROMs as they have the same address as they are using a shared i2C bus.

This has led to version 1.4 of the SAO Tester board. Here I am using a i2C bus multiplexer so that each SAO Port can be on it's own i2C bus. Just to be safe I am also switching power to each Port. This way I can measure how much power each board is using and more importantly it will allow me do a kind of 'semi Hot-Swapping' of a SAO board. Of course, I will have to do this under software control, so maybe the user presses two buttons on the Tester to turn off SAO Port power and i2C, then they are free to safely swap out the SAO Hat. Pressing the buttons again will re-enable the SAO Ports and the MCU will re-read the Ports to determine whats plugged in.

The Tester Version 1.4 uses a INA219 voltage and current sensor that can be used to monitor the power for each of the SAO Ports. There is no local display attached to the board, so the results will be published via a locally hosted webpage that can be monitored via your mobile phone etc.

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You can find my SAO Tester PCB design files and example software here: https://gitlab.com/parkview/Simple-Add-On_Tester_PCBs

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Hawk volunteered to design up the the conference badge and is based around the Nations Tech: N32L406 MCU, something like this: https://www.lcsc.com/product-detail/Mic ... 81444.html This is a low power MCU and in fact the board ran the OLED display and 12 RGB LEDs for nearly a week 24/7 on a single AA battery. A very impressive design and software engineering, thanks Hawk!

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You can find the badges KiCAD design files and software here: https://github.com/ExponentialDeepSpace ... sia-Badge/