ATM90E26 FeatherWing
NOTE: Please only use a maximum of 12VAC rms transformer with the featherwing to avoid LDO overheating. LiPo may also be needed for high/continuous wifi usage since LDO voltage may sag. Pin header not include.
What is it?
An advanced Energy Monitor Featherwing capable of class-1 operation with appropriate Current Transformer and Potential transformer powering it.
Why did you make it?
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 planned to eventually make it into a single board /accurate wifi enabled Energy Monitor. For now it is living next to a Feather Huzzah 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 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 the 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.
Meanwhile I put it all together into a featherwing form factor for PCB manufacture to make it a more complete dev-kit for easily testing the capabilities of the ATM90E26 in conjunction with all the other devices in the Adafruit feather family.
What makes it special?
This board in combination with a few Feathers and Featherwings can provide the functionality of the several hundred dollar Atmel devkit, it is also more flexible and cheaper than the Smart Plug. However Atmel products are very well engineered and I highly recommend trying them if you have the budget.
This is also a fully open source design (working on my OSHW certification), you can get a tested board from me or order one from PCBs.io which will give me some credits towards more boards.
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