“A while ago I started using home assistant on a pi and bought some inexpensive 433Mhz ac wireless switches. However, after one month of intense use the Raspberry Pi didn’t have enough power, so I bought a cheap computer of eBay for this purpose and it worked well expect that I didn’t have control over my switches. Sure I could have use the raspberry in conjunction with the computer but that would be overkill, so I started designing an Arduino on a stick with USB and 433Mhz tx and rx. The first design I made was way too optimistic I planed to use a rf switch to switch between rx and tx and use a single sma port for the antenna but that didn’t go so well and neither tx nor rx was working, so I just gave up for a few weeks and then made version two.
Version two is smaller and have two coiled antennas instead of a sma port and it works well enough. It’s still based around an atmega328 running at 16MHz with the Arduino UNO bootloader and a CH340 USB to Serial converter. As it’s so versatile in its operation, I also added expansion port for SDA / SCL / A0 / Pin8 (PD0) in addition to the iscp header with the spi bus so that the board could be used as standalone transmitter to send sensor values for example.”