Some LED circuits explained examples from various projects: flashing LEDs, 220V LEDs and more.
We start by showing you the LED circuit in series with a resistor. You must make some calculations to figure out the resistor value, depending on voltage power supply, LED voltage drop and desired current.

There are many ultrasonic pest repellers available on the market but a major drawback is that their power output is low and their effectiveness suffers. The electronic pest repeller generates powerful ultrasonic signals to repel pests.

This simple and cost-effective ding dong electronic doorbell circuit is based on IC 8021-2. The IC has an in-built circuitry to produce ding dong sound each time its pin 3 is pulled low. The sound is stored in the IC as bits, as in a ROM. The sound output from the IC can’t however drive a speaker directly, as this puts strain on the device.

This home smoke detector circuit warns the user against fire accidents. It relies on the smoke that is produced in the event of a fire and passes between a bulb and an LDR, the amount of light falling on the LDR decreases. This type of circuit is called optical smoke detector. Do not use it as a home smoke detector it’s jus for electronic projects.