Dark-Detecting LED with Only 5 Components
2016-07-08 | By Nick Normal
License: General Public License
Abstract Overview
This is an abstract only. For full project details, see Dark Detecting LEDs.
If you’re looking for an introductory project to electronics, this dark-detecting circuit might be the project for you. The circuit turns on an LED when light in a room begins to darken. Typical applications for this circuit include night-lights, safety lights, etc.
For this project you need a battery, a phototransistor, an LED, a resistor, and a transistor. The transistor is a 2N3904, which is a common low-power NPN transistor used in many hobby electronics projects. When light hits the phototransistor, the transistor and the led are effectively switched off. But when there is no light present, current freely passes through transistor’s Collector-Emitter junction and lighting up the LED.
Despite only having a few components, it is always best to prototype your circuit on a breadboard. It is worth noting that you will not be able to simply replace components directly. The LED, for example, cannot be simply replaced with a white or blue LED due to differences in forward voltage and other specifications. Prototyping first on a bread board, you can make sure that everything is in order before you commit to soldering the parts.
Once everything is soldered and confirmed to be working, you might want to put a level of protection to your circuit since some of the parts need to be left uncovered: this might lead the parts to be damaged. For this project, you might want to try U Mold, which when heated forms a transparent putty-like substance that you can use to cover your circuit. Be sure to make it in such a way that you still have access to the battery in case it needs replacing.
The Dark-Detecting LED is a fun and simple circuit that can be done by anyone at any level. It can be a great gateway project for more advanced implementations. Experiment! Try out new LEDs, or other sensors, think of practical ways where you would need a dark detecting circuit. Experiment and make this project truly yours!
Have questions or comments? Continue the conversation on TechForum, DigiKey's online community and technical resource.
Visit TechForum