Matrix user forums

Hello,

I bought the stainless steel temperature probe, and I managed to get measured values on my LCD display. Values between 0 and 1024.
My question is: how can I get the right values in degrees Celcius
from these?
Is there somewhere a table with the right values?

Best regards,
Ronny

The formula for getting the temperature can be found in this document, but be warned that is is a bit complex:

http://www2.vernier.com/booklets/tmp-bta.pdf

How do I get the value for the 'R' that is used in the formula?
With flowcode I read a value between 0 and 1024.
How can get from this the value for the 'R' that is neede
in the formula?

Sorry, I haven't got time to give a thorough answer because I'm about to go away for a week. But I can point you in the right direction.

From my memory, the sensor is connected to the PIC with a pull-up to Vcc - I think this is 10k or 20k. This forms a potential divider with the R value of the probe internally connected to ground. The PIC's ADC input value is approx 1023/2 (i.e. 511) for a 2.5V input (assuming a 5V power supply). This voltage will be present when the resistance of the probe is the same as the pull-up resistance.

Hi Ronny,
The value of R (in Kohms) is the relative resistance value of the temperature probe at a given temperature. This value as stated is non linear so you will need to decipher the equation in the document in the previous reply.