PIC CW Temp Circuit

  
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Remotly check the temperature of a few things, in my case the repeater site at GB3PY. A system which used a radio to receive requests for the currenttemperature and send the results back to the user. Requests are by DTMF tones and the response is in CW, mores code. The full design has not been tested, but I`ve managaed to do it with 2 sensors which works fine. This is an ongoing project and after a request
PIC CW Temp Circuit - schematic

from a friend about using PICAXE to decode DTMF I thought I would post details of the project which demonstrates the wayI do it. The PICAXE code, schematic and PCB layout are all available todownload below. The code has afew things worth mentioning in it. When the HT9170B DTMF decoder chip gets a valid DTMF tone it outputs the value in binary (check the datasheet) but DTMF 1 outputs binary 1 or 0001 and DTMF 8 outputs binary 8 or 0100. Not only this there is a line called DV, pin 15 on the HT9170B which goes high when a valid DTMF tone is decode, this is great cause it is a way to tell the PICAXE it is time to read the input pins. You`ll see this in the code on line 41 if pin4 = 0 then goto start`. Basically I have a pin set in the code, this is between lines 42 and 72 and if the valid pin is entered then we read the temp and respond. The code below should be enough to read the DTMF value and store is register B0 using just the DTMF chip and PICAXE. so B0 is the actual value of the DTMF key pressed.



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