UPM manufacurs wireless thermometers and weather stations. The temerature sensors communicate via a radio protocol with the base station.

The protocol sent from the sensors is actually a digital protocol which is AM decoded over 433.92MHz radio signal. The bit rate of the protocol is actually slow enough to be sampled by the microphone input of a regular PC, so this is the interface we use. All wee need is to find the decoded radio signal, adapt the level and feed it into the microphone input. The NetHome software does the rest.

When we open the base unit, we see that UPM has made it easy for us, the radio receiver unit is a separate card (down to the left) where the decoded radio signal is avaliable!

All we have to do is to adapt the signal level of the decoded signal to the microphone input and mount a 3,5mm microphone connector to the UPM case. The circuit needed to adapt the signal is the following: