Hacked Gadgets Forum

May 6, 2010

PIC 12F683 based Temperature Monitor

at 8:09 pm. Filed under Electronic Hacks

temperature-monitor-pic-based


If you need to do some temperature monitoring over a long period of time this is the device for you. It can store 32 thousand measurements and has a current draw of only 50uA. The top picture is version 1 and below is a shot of the surface mount version 2.

Via: Electronics Lab

“The PIC software is written in assembler and based on earlier projects using I2C interfaces. The EEPROM, PIC and external connector all share the same I2C bus and the PIC will not use it unless the thermistor is fitted. The EEPROM address keeps incrementing in this case so that breaks in the data can be seen.

When the temperature measurement is not being made the PIC goes to sleep. It is woken once a second (using an external crystal oscillator and internal counter) to check if it is time to make a measurement. The sampling interval is stored in a fixed location in the external EEPROM and is read at power up.

The thermistor and a resistor form a potential divider that is measured by one of the ADC channels on the PIC. This is measured four times and the four results are added together. This gives a slightly better measurement since the average of four readings is likely to be closer to the true value than a single measurement alone due to the noise present in the circuit.“

temperature-monitor-pic-based_2