The AudioProtocolTransmitter module, can encode digital protocols as audio signals from the sound card/audio output from a PC. To be able to transmit the signals, some kind of hardware is needed. This is a description of how to build a generic RF-transmitter working on the 433MHz band.

The first step is to transform the low level AC output signal from the sound card to a digital signal strong enough to drive a transmitter. This is done with a simple OP-Amp circuit as follows:

The OP-Amp can be any general purpose type which can handle single power supply and high power output.

The easiest way to build the transmitter is to modify an existing one. I took an ordinary Nexa remote control, disconnected its logic chip and hooked up the output of the OP-Amp to the transmitter stage of the remote control.

This is how the remote control looks (to the right):

Disconnecting the logic chip requires a steady hand, here are the steps:

Locate the signal output pin from the chip. This is where the digital protocol is sent to the RF-transmitter stage.

Cut the track on the board from the output pin and the pin next to it, remove the surface mounted capacitor. This is a bit tricky, because the tracks are small…