This equipment 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. Electric cost will become high if an air-conditioner is always operated. Then, 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.
- LED display and SW reading circuit
7 bits of low ranks of PORTB are used for lighting of 7 segment LED, and reading of BCD switch in common. PORTC and the 8th bit of PORTB is used for designation of a device. The mode change of PORTB is required of LED control and BCD-SW control. This change is performed by software.
The diode connected to the BCD switch is for prevention of illegal current. With a BCD switch, a common terminal and each terminal corresponding to a bit short-circuit by setup. If there is no diode, the setting state of a switch will influence operation of other devices. In the case of a silicone diode, VF is about 0.6V. When L level detection of the PIC cannot be normally carried out with this voltage, it is better to change a diode into other kinds.(Germanium etc.)
- External equipment drive circuit
This is the circuit which controls external equipment. Although based on the drive current of the relay to be used, in this case, the drive circuit which uses a transistor is adopted.
- Temperature sensor circuit
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.
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