PCB & Mechatronics Design

This circuit is designed to use a photoresistor sensor to measure the amount of light in a room and comparator operational amplifier to determine if an LED should be turned on or off accordingly. This system consists of:

​

• 10K resistor (x3)

• 1K resistor (x1)

• Photoresistor (x1)

• Comparator Operational Amplifier (x1)

• LED (x1)

• 100 uF Capacitor (x1)

​

An operational amplifier is used to compare the voltages between two voltage divider configurations, one with a 10K resistor and photoresistor, and the other with two 10K resistors. As the amount of light received by the photoresistor decreases, the resistance of it increases, resulting in a higher output voltage from the voltage divider. An opt amp is connected to 9V and GND for its positive and negative voltage terminals. The opt amp has two connection pins, a non-inverting input that connects to the photoresistor based voltage divider, and an inverting pin that connects to the other voltage divider. When the photoresistor receives significantly less light, the voltage at its connected opt amp pin will increase and be higher than the other pin, connecting the 9V to the opt amp output pin, which powers the LED. When the photoresistor is exposed to more light, the voltage at its designated opt amp pin will be less than that of the other voltage divider, therefore the opt amp will connect the output pin to GND and the LED will not light up.

A capacitor is also included in the circuit to stabilize fluctuations and spikes in source voltages.