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Temperature data format
For the purpose of transmitting temperature data from the sensor to the receiver, a dedicated data format has been designed. There are several points which enable reliable and long lasting operation of transmitter-receiver pair worth mentioning:
Putting all this together, a code word consisting of five 8-bit IR bytes emerges. At data rate of 1kbps, the complete emission lasts merely 1/25 second. One such short code word is emitted every 30 seconds which means that IR communications channel gets occupied 1/600th of overall time. That is good for two reasons: 1) Battery drain is very low. Despite IR LED conducting up to 500mA of current from batteries while emitting IR bits, average current consumption is barely 80ľA which leads to more than a whole year of uninterrupted thermometer operation from a single battery pack. 2) IR communication other than thermometer data transfer can take place in the same room inside which a remote thermometer operates. Therefore, using a TV remote control is as easy as usual even if more than one thermometer unit is active in the same room.
In order to enable using standard IR remote control receiver modules, IR bits are On/Off keyed at the rate of 38kHz. This means that each bit is transmitted as a short burst of 38kHz IR impulses. Most IR receiver modules put some constraints on bit duration which has been taken into account when designing the data format. There is a broad spectrum of cheap yet extremely high quality rceiver modules on the market. The most popular ones belong to TSOPxxxx family produced by Vishay (Siemens).
designed by LP 2011