I was struggling very much to get an ESP-12-E and a RFM95 to work together and run LMIC, and transmit a packet to TTN. The biggest issue I had was figuring out which pins on the ESP should be grounded, and which should be pulled high. And when and in which order. I finally got the whole thing working yesterday.
In this post I'll give an outline of how I connected everything. Next time I will hopefully summarize what I had to do to get the software side working, as different library versions caused some headaches.
The ESP8266 module I have is this one: http://www.esp8266.com/wiki/doku.php?id=esp8266-module-family#esp-12-e_q
My final connection diagram looks like this:
Things to take note of:
- The ESP should be powered from an external 3.3 volt source, not via USB. Big capacitors are needed to suppress the spikes of current the ESP module needs during startup. USB does not like big caps on its voltage lines.
- The ground connection of the ESP should be connected to your power supply and the USB-UART (FTDI) board.
- Note the pull-up and pull-down resistors on pins GPIO0, GPIO2, GPIO15, EN and Reset of the ESP module. This is very important for the ESP to boot up into the correct mode, as well as the SPI slave select line to work.
- To boot the module up in programming mode, hold down switch "Program", then press and release switch "Reset", and then release switch "Program". After a successful program, press and release the Reset switch to boot up into normal mode.