This is a simple project that uses an AdaFruit Huzzah, a 0.96" OLED, and a serial port to interface with an X-10 Firecracker CM17A to control X-10 modules with OpenHAB. The device fits into a small box and is only marginally larger than the firecracker itself. I decided to use an AdaFruit Huzzah because it was slightly smaller than the NodeMCU and it gave me the option of using a Lithium-Ion battery, which I wasn't quite able to fit in the box.
I used hot glue and an X-Acto knife to create a spot for the board to sit in so the MicroUSB port would be right up against the box. I used 6mm long M2 screws and a little thread locker to hold the OLED against the top of the box. To use it, you obviously need a X-10 FireCracker, but also a receiving unit to receive the radio signals and transmit to the rest of the house.
Another feature I added was to shut the screen off after 5 seconds (or whatever you decided or even not at all) because I didn't like the bright light at n