This is an update of the Nixie Thermometer/Hygrometer (110321-I) published in the June 2012 issue of our magazine. In the original design a small SHT21 sensor carrier PCB was connected to the main board via a four wire cable (I2C bus plus power supply lines) . Now this cable is replaced by two small microcontroller boards establishing a wireless link using two RFM modules. The remote PCB carries the sensorboard and is powered by one CR2032 lithium battery.
No modifications of the original boards needed, just plug & play. The pictures show our prototype with the 433MHz version of the RFM12 modules, but also 868MHz and 915MHz versions will be supported.
Since the circuit for the transmitter and receiver are almost identical, only one PCB layout is needed. The shape of the PCB is designed to fit exactly on the corner of the main PCB.
PCB and programmed controllers can be bought at the Elektor shop: