This is really Simple level voltage detector circuit. I like it so much because cause me to know principle about comparator circuit form like.
As show in Figure below, We use LM741 OP-AMP circuit highly popular is the base of a circuit.
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As the video below. When we set all components to breadboard successfully. Suppose, we need to detects voltage 2-volts.
I test this circuit with firstly to apply a 9-volt power supply to the circuit. Then, with rotate or adjust a VR1-potentiometer in the breadboard to set a reference voltage to pin 3 (read digital multimeter left is 2-volts), After that apply an input voltage to the INPUT at pin 2 of IC1.(read voltage as Zero) Now LED go out. I used to measure output voltage equals the power supply voltage 8.4V approximately.
Then I increate voltage at pin 2 continuously until to 2-volts as volts multimeter. It is making LED glow on immediately. Although we still add voltage up too many voltage. I used to measure voltage at output as 2-volts it lower than the positive (9V power supply) voltage so LED glow.
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Therefore, When voltage at pin 2 larger than pin 3 cause output pin 6 as low voltage when compare with ground so LED light up.
The resistor-1K is used to control the current to LED1.
3 Others circuit using 741 voltage comparator
1. Simple temperature sensor diode 1N4148
Learn how to use a diode to sensor temperature. The voltage across the diode gets slightly different voltages. We can use 741 op-amps check it easily.
2. Car overheat alarm circuit
We apply Thermistor for this circuit. It is a better diode. Also, we use 741 op-amps as a comparator circuit.
3. Automatic Op-amp night light circuit
Also, this circuit we use 741 op-amps to detect a level voltage across a voltage divider. They include LDR and potentiometer.
The event above circuits is old. But now they are still working. Of course, you can learn Electronics with them.
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