Inverting Detector Circuit

This is a design circuit for basic infrared and visible inverting detector circuit. This circuit is use LM339 voltage comparators are the active element for the controller. Here’s the figure of the circuit;

All of the comparators on the PCB are wired so that when the photo sensors are dark, the output of the comparators will be LOW and the LEDs will be ON. The detection voltage level for the circuit as shown is set at 1/2 of the supply voltage. If a lower or higher detection level voltage is needed, the values of resistors R9 / R10 and R19 / R20 can be adjusted. This circuit does not need a regulated power supply and can operate on supply voltages of up to 32 volts. The 1K output resistors can be replaced by jumper wires if they are not needed such as for inputs to control or signals circuits that have their own current limiting resistors. For phototransistors a value of 470K ohms will work for most room light situations. If the light is dim, selecting a higher value resistor such as 1 Mega ohm will give better sensitivity. This High Impedance Test Voltmeter circuit can also be used for testing phototransistors installations.