Calibrating temperature in PIC based temperature controller - Electronic Circuits Projects Diagrams Free

Shohadawy · 23rd February 2008, 06:48 AM

How can I calibrate the voltage of a thermocouple connected to a pic16f877 so that I could view this voltage as its corresponding temperature on an LCD display.... In the attachments there is a picture of the complete circuit of the system that I'm talking about .... a PIC based temperature controller

Diver300 · 23rd February 2008, 08:23 PM

It should be a fairly straightforward to read the ADC and transfer the result to the LCD.

I assume that you are using the 5V supply as the ADC reference. If so, the ADC will read 0 at 0V and 1023 at 5V input. That will give about 2.048 counts per degree centigrade.

You will need to get the PIC to do some maths to get the result as deg C, which you can then send to the LCD.

However, I think that is a difficult way to measure temperature. If you need a wide temperature range, use a MAX6675 which converts thermocouple to 3-wire with one IC, no analog to deal with and no power supplies other than the 5V.

For temperature ranges up to about 150 deg C, you can use a temperature sensing IC that doesn't need a separate sensor, such as an LM95071

Shohadawy · 23rd February 2008, 08:43 PM

Then , if I used the max, will its output represent the temperatures directly without calculations..and so can I display this digital signal directly on the lcd so the temperature is displayed directly

Diver300 · 23rd February 2008, 09:29 PM

Sort of.

The output is in binary, and it is 16 bits long. Look at the data sheet.

You will need to shift the result to the right by 5 bits to get the result in degrees C, which will be two bytes if you are wanting to have temperatures above 255 degrees C

However that will be in binary, and you need to convert to BCD to make it meaningful. You can look up BCD routines in the application notes at www.microchip.com or the examples at www.piclist.com

Shohadawy · 23rd February 2008, 09:32 PM

Thank you very much

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23rd February 2008, 08:23 PM	(permalink)
Diver300	It should be a fairly straightforward to read the ADC and transfer the result to the LCD. I assume that you are using the 5V supply as the ADC reference. If so, the ADC will read 0 at 0V and 1023 at 5V input. That will give about 2.048 counts per degree centigrade. You will need to get the PIC to do some maths to get the result as deg C, which you can then send to the LCD. However, I think that is a difficult way to measure temperature. If you need a wide temperature range, use a MAX6675 which converts thermocouple to 3-wire with one IC, no analog to deal with and no power supplies other than the 5V. For temperature ranges up to about 150 deg C, you can use a temperature sensing IC that doesn't need a separate sensor, such as an LM95071

23rd February 2008, 08:43 PM	(permalink)
Shohadawy	Then , if I used the max, will its output represent the temperatures directly without calculations..and so can I display this digital signal directly on the lcd so the temperature is displayed directly

23rd February 2008, 09:29 PM	(permalink)
Diver300	Sort of. The output is in binary, and it is 16 bits long. Look at the data sheet. You will need to shift the result to the right by 5 bits to get the result in degrees C, which will be two bytes if you are wanting to have temperatures above 255 degrees C However that will be in binary, and you need to convert to BCD to make it meaningful. You can look up BCD routines in the application notes at www.microchip.com or the examples at www.piclist.com

23rd February 2008, 09:32 PM	(permalink)
Shohadawy	Thank you very much