I am constructing a multi channel temperature data logger.
I wrote some codes in mikroC to test which channel is connected to thermocouple. The codes was attached as well. However, the result was not satisfactory. The results from RA1 pins (analouge input voltage pin) were stored in eeprom even the pin was left floating. The voltage at RA1(analouge input voltage pin) was non-zero when the input pin was left floating. I think this is electronic problem. The schematic diagram of the circuit was attached. Can someone help to figure what problem??
Thanks.

 

Any input pin will float to some level if not pulled explicitly high (or low) with a resistor. See what size is recommended in the data sheet.

That 1458 is a bit dated. You must have got the schematic from a device built some time ago.

I guess you have a table in the uC to correct the thermocouples' readings? I did not see an ice point reference.

I would think battery life would be considerably extended if the logger did not run continuously.

 

I am constructing a multi channel temperature data logger.
I wrote some codes in mikroC to test which channel is connected to thermocouple. The codes was attached as well. However, the result was not satisfactory. The results from RA1 pins (analouge input voltage pin) were stored in eeprom even the pin was left floating. The voltage at RA1(analouge input voltage pin) was non-zero when the input pin was left floating. I think this is electronic problem. The schematic diagram of the circuit was attached. Can someone help to figure what problem??
Thanks.

You might want to use a conditioning amplifier between the thermocouples and the analog inputs...I imagine they're very high impedance, and subject to stray signals, if not dealt with deliberately.

eric