Hobby Projects - Insulation tester, LED Circuits, Meters.

Saturday, October 21, 2017

Simple Cheap Dark-Detecting LED Circuit

Here's a simple problem: "How do you make an LED turn on when it gets dark?"  EMS Labs.

Simple Cheap Dark-Detecting LED Circuit

When light falls on the phototransistor, it begins to conduct up to about 1.5 mA, which pulls down the voltage at the lower side of the resistor by 1.5 V, turning off the transistor, which turns off the LED......

Simple Cheap Dark-Detecting LED Circuit

Parts -On top: a CR2032 lithium coin cell (3 V). On the bottom (L-R): the LED, an LTR-4206E phototransistor, a 2N3904 transistor, and a 1 k resistor. This LED is red, blindingly bright at 60 candela, in a 10 mm package. It casts a visible beam, visible for about twenty feet in a well-lit room.