pic microcontroller based temperature monitoring and control

[scientistumair]

I am new in microcontroller. I have task to design pic microcontroller based temperature monitoring and control using pt100 as sensor. Total 8 pt100 are to interface with pic16f877a. Set points are to be given by keypad and display should be on lcd. Control technicque should be pwm.I am using CCS compiler
First I am controlling and display 1 temperature(i.e. using 1 pt100)
Can single pic16f877a controller can do this task?
I have following difficulties:
when I interface pt100 to pic then my pic doesnot read analog voltage voltage drop to constant -0.875volts at input of microcontroller. Circuit is as follows
1ma current source-voltage follower-noninverting amplifier-pic16f877a
I am using lm324 quad opam ic for current source and for amplifier.
Second how to develop variable pwm in pic using pic(difference b/w set point and process variable=pwm duty)
Third how to interface keypads.Should I have to interface rs485 for communication?

 

[rajbex]

I can't see your circuit. But yes, you can read temperatures from 8 analog sensors, interface a keypad, and LCD screen to PIC16F877A. A 4x4 Keypad can be interfaced using 8 pins of microcontroller. There is no need to know about RS485 for this. Search on google for Keypad interfacing.

- Raj
Experiments with PIC16F628A

 

[scientistumair]

ok thanks. But what type of control technique(e.g. pwm pi or pid) should I have to use? Can I also use 8 pins as output for 8 different heater's control?

 

[rajbex]

If you just want to turn heater On and Off, you don't need to use PWM. You can simply use relay switch for that purpose. There are altogether 33 I/O pins in a PIC16F877A, so I think you can reserve 8-pins for individual heater control.

-Raj
Experiments with PIC16F628A

 

[scientistumair]

pwm or pi control is required

If you just want to turn heater On and Off, you don't need to use PWM. You can simply use relay switch for that purpose. There are altogether 33 I/O pins in a PIC16F877A, so I think you can reserve 8-pins for individual heater control.

-Raj
Experiments with PIC16F628A

thanks. But I dont want to use on/off control because it will cause great overshoot and I want to control with large accuracy.I want to use pwm or pi control.