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Simple level voltage detector using LM741

This is really Simple level voltage detector circuit. I like it so much because cause me know principle about comparator circuit form.
As show in Figure below, We use LM741 OP-AMP(IC-741) highly popular is base of circuit.

Simple level voltage detector using LM741

As 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-volts power supply to the circuit. Then,with rotate or adjust a VR1-potentiometer in 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 (power supply) voltage so LED glow.

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 current to LED1.

This Post Has 2 Comments

  1. Have a circuit that comes from the dash info center of my Dodge Diesel, it is the low fuel level reminder light driver. It appears to be an Op amp( 8 pin ) and a power transistor. Neither of these parts have #’s which I have been able to use to identify them with. The light will not go off no matter how much fuel is in tank. The circuit is no longer replaceable from the Dealer as it is too old a model. IC # is CB9047n — Transistor # is simply 6209 thought possibly this # might be a Vreg. The circuit has a lot of components just to be a driver such as a voltage to current converter which is what I surmise. There are only 4 connections to the board, so 1 has to be V+, 1 v-, 1 going to the light, and 1 coming from the gauge sending unit, which has 3 wires to it, +,- and the signal wire which is a variable voltage. If the parts can be identified, I would use a replacement of similar value and rebuild the board. If not I must make a new board that will do the same job, turn on the filament lamp when the signal from the sensor reaches a set V. and turn off when the V is out of low limit range. I have some ideas on how this should be done, but starting over from scratch will be more work then simply repairing the original circuit. Got any suggestions?

  2. find that the op amp is a dual so it will not be difficult to replace this if the part does not a critical spec sheet,which I doubt it does. So it looks like I’ on the way to getting it figured out. Still welcome any info or suggestions.

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