A lot of remote sensing thermometers have a problem with measuring more than one temperature at a time. To overcome this problem, a different technique is adopted here, which allows you to sense eight (at the most) transducers at a time.
Block diagram of the wireless addressable digital thermometer is shown in Fig. 1. At the transmitting end, an 8-bit analogue-to-digital converter (ADC) continuously scans and converts signals from eight different temperature sensors. The sensors are selected sequentially by a 3-bit binary addressing system. At any moment, output of the ADC is an 8-bit binary number representing the analogue signal developed at the output of a particular temperature sensor, being addressed at that moment.
By using special parallel-to-serial encoders, this 8-bit data, along with the binary address of the sensor, is sent serially to the remote receiving end. Communication between the two ends are met with the help of a pair of 433MHz UHF transmitter and receiver modules operating in ASK/OOK mode.
At the receiving end, the transmitted signal is received by a 433MHz ASK/OOK RF receiver module. The received 8-bit serial signal is then converted back to its original parallel form, by using special data decoders as explained later. An equivalent analogue signal is then developed from this data by an 8-bit digital-to-analogue converter (DAC). A digital multimeter connected at the output of the DAC is used to show the temperature on mV scale.