Monday, October 10, 2016

ATM90E26 + ESP8266 Energy Monitoring

Before I commit a design to a PCB, I usually make a messy jumpers everywhere version on a breadboard. This is not always possible for a full complex design, often sections get committed to PCB and then modules find a home on the overall breadboard prototype.

This has been the fate of my ATM90E26 Breakout. I plan to eventually make it into a single board /accurate wifi enabled Energy Monitor. For now it is living next to a NodeMCU on a breadboard. The ATM90E26 has the flexibility to be accessed both over SPI and UART. However the SPI mode it supports is only Mode 3, which is an unsupported mode of the ESP8266 Arduino stack. So I ported my ATM90E26 Arduino interface code over to UART mode with CRC check and everything worked okay after a few days of head scratching. You can find it on the UART branch in github.

I would like to build a self-powered energy monitor, so I pulled out a venerable 7805 and added it to a half-wave rectifier from the 12V AC-AC transformer used for voltage waveform sampling. When I was using a full-wave rectifier in the past the overall DC voltage was too much for thr 7805 to regulate without a heatsink, however with the 1/2 wave version, the diode takes care of dropping half of the voltage leaving the 7805 functional without a massive heatsink.

I calibrated the set-up with some magic multipliers found using the datasheet, maths and my 116W calibration lamp and it all works like a charm as shown in the video below.

There seems to be some noise leakage onto the UART when AC signals are applied, I will attempt to rectify this with an optoisolator. However a simple reboot of the ESP8266 platform seems to quickly fix any software serial communication issues. Meanwhile I am putting it all together into a featherwing form factor for PCB manufacture.
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