We’ve seen no shortage of projects that use the ESP8266 or ESP32 to add “smart” features to existing home appliances, often by pairing the microcontroller with a radio or IR transmitter. If your device has an existing remote, integrating it into a custom home automation system is often just a matter of getting a few cheap modular components and writing some simple code to glue it all together.
But what if the appliance you want to control doesn’t use a common frequency? That’s a question that [eigma] recently had to answer after finding the remote control for the bedroom ceiling fan was operating at a somewhat unusual 304 MHz. Something like the MAX1472 could probably have been tuned to this frequency, but the chip doesn’t seem to be available in a turn-key module as the popular 315 MHz transmitters are.
There were a few possible options, including using a software defined radio (SDR), but [eigma] didn’t want to spend a fortune on this project or wait months for parts to get shipped from overseas. The most straightforward solution was to design a custom transmitter tuned to the proper frequency using discrete components; something of a dark art to those of us who’ve been spoiled by the high availability of modular components.
What follows is an fascinating look at the design, testing, and troubleshooting of a truly scratch-built transmitter. You won’t find any ICs here, the carrier signal is generated with just a transistor, some carefully measured pieces of wire, and a handful of passive components. By modulating the signal with an ESP32, [eigma] successfully makes the oddball ..
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