A temperature controller with PIC. It uses two temperature sensors, drives external equipment, and keeps the temperature of the room at preset temperature. The purpose of this equipment is for preventing room temperature going up with the heat of the computers.
I made the equipment which adjusts the temperature of the room automatically using some ventilation fans. The function below preset temperature is a function attached moreover. I think that it can use for temperature control, such as a greenhouse. Control mode(works over preset or below preset) is changed with a switch.
Here two temperature sensors are used. One is indoor temperature detection and another is open air temperature detection. The ventilation fan to be used is the type which performs inhalation of air and an exhaust gas simultaneously used in a bathroom etc. An open air temperature sensor is for stopping a ventilation fan, when the temperature of the open air is higher than an indoor temperature. Open air temperature detection is used only when using a ventilation fan in summer. Since a winter season does not need to take the open air into the room, control by open air temperature is not carried out.
A temperature sensor (LM35DZ) can measure from 0°C to 100°C. However, the output is 0V at 2°C. Therefore, the voltage of minus is required in order to measure 0°C. Since the minus power supply is not used with this equipment, the measurable temperature is above 2°C. The output of a sensor goes up by 10mV for every 0°C. The output voltage in 32°C is 300mV.
The output voltage of a sensor is amplified by an operational amplifier, and is inputted into the A/D converter of PIC. Proofreading of a temperature display is performed by adjusting the gain of an operational amplifier by VR. In this circuit, in order to simplify a circuit, the operational amplifier which operates with a plus single power supply is used.
http://www.hobby-elec1.org/e_pic6_g.htm
