Hi there!
Awesome little product - thanks for all the time and effort that’s gone into it. I’ve just built my own and have the unit running fine except for one strange issue. The board doesn’t seem to want to boot with the SD card installed. Once I remove the SD card the board will boot and pause waiting for the SD card to be installed - once it’s installed it starts and runs fine. Any ideas? Something interrupting the SPI bus, is this a known issue?
Thanks!
Alex
No, no known issue. Sounds like an electrical problem. That’s the fun of DIY, you get to debug it too.
Thanks for the quick reply overeasy 
I did sort this out and sharing my findings incase anyone else comes across it. The ESP8266 uses pin 15 (D8), which the IoTaWatt uses for the SD Card CS pin as a ‘boot from SD card’ hardware option if it’s high for 250ms during boot. The -01 series incorporate a 10k pull down resistor between pin 15 and GND on the board however the -12 series do not. This is characterised by the device not booting and the ESP console monitor hanging at “waiting for host” when an SD card is installed.
This is easily overcome by putting a 10k resistor between D8 and GND.
Can you point me to the information on the “boot from sd card” option? That sounds like it might be useful.
Any particular reason you chose the ESP01 when there are tons of cheap ESP12 nodeMCUs available?
Didn’t do it on purpose, was more a question of what my local supplier had (in Australia) and my impatience. I originally bought a NodeMCU v3 which was is a different size profile (didn’t know that at the time, this was my first time working with a ESP8266 > than the Huzzah).
This was the original post that I found:
https://www.esp8266.com/viewtopic.php?f=6&t=1982
And more digging led to this:
http://www.forward.com.au/pfod/ESP8266/GPIOpins/index.html
It’s referred to as “flash boot” in the datasheets, don’t have a reference handy. The software runs fine on the ESP01.
Alex