Testing
Writing the firmware steadily opened up each feature of the board and I was quickly able to sign off everything as working as designed. An advantage of using the MCU embedded in the Arduino is that there’s a lot of open source code out there to drive ICs and MCU peripherals. Not all of it is great, but even the low-quality code can give you a head start with the fundamentals of how to begin.
I was able to re-use a character font library for the MAX7221 and the popular ‘Wire’ library for driving the I2C peripheral that I needed to talk to the INA226. Here’s a picture of the device up and running, supplying 95mA to a test load.
I’m going to design a case for this power supply with switchgear and banana sockets on the front but until that comes I needed a quick hack to access the switches and the rotary encoder. I did this with a dremelled and drilled piece of stripboard that I could push the switches through and solder them to some access wires on the copper side.
It’s a hack, and it’s had to be patched up once already but it has allowed me to get through this testing phase without a real case.
The temperature monitoring and dynamic fan control also seem to be working well. Here’s a snapshot of the configuration menu item that displays the current temperature.
Now let’s take a look at the data logging. I hooked up the UART pins to one of those little adapter boards that you can get on ebay. The protocol is 19200-8-N-1.
This allowed me to connect a serial cable to the back of my PC and receive the logged data. Each line of data contains the millisecond timestamp of the sample, the voltage and current readings and the 8-bit CCITT CRC of all characters preceding the CRC number itself.
The default configuration transmits a new line once per second but this can be modified in the configuration menu.
