al salam aleikom,

Problem Description
I have built a plant consisting of:
1- A heating room.
2- A heater. (220V AC)
3- A sensor. (Thermistor)
The reading of the sensor is converted into a (0-5V) signal using a traditional signal conditioning circuit.
Then this signal is read by a PIC16F877 using the A/D module then a control decision is made.

The problem
How can I represent the control decision and send it back to the heater?
I thought of a PWM signal controlling the heater current. However, I don't know how to interface the uController signal into the heater 220V AC circuit.
One of my friends suggested a TRIAC but I'm not sure if this may help.

Any suggestions?

 

Hello,

Perhaps you can use a part of the dimmer circuit descibed on this page.

http://sound.westhost.com/project62c.htm

You could connect R4 to the output of the pic.

Best is to sync the pic with a zero crossing detector and generate a pulse depending on the power needed.
When you reduce the powersupply of the rampgenerator, on the collector of Q2 is the zero crossing signal.

Greetings,
Bertus