Circuit Library

This is an op-amp circuit that turns on a fan when the temperature goes above a certain threshold. The threshold can be adjusted with a potentiometer.

Never built a circuit before? Then start here. You can build this in a couple of minutes. It's a simple LED circuit that's powered by a 9V battery.

This shows a very simple flashlight project with a LED and a resistor. The switch controls if the light is on or off. Build this into a small casing, and you have yourself a homebuilt flashlight. You can use any battery voltage for this, as long as you adjust the resistor value to match.

Do you want to know when there's a bird in your bird feeder? There's a circuit for that! This uses a PIR motion sensor that works with infrared light. And it will light up an LED when there's a bird moving inside the feeder. A PIR sensor stores an image of the infrared light it sees. Then everytime it sees a change in this image, for example from a bird moving, its output will go HIGH for a period of time.

This project sets up two flashing LEDs, one red and one blue, to create a police lights effect. You can use this circuit to integrate into a toy, or just to practice your circuit building skills. The circuit is built around a [555 timer](https://www.build-electronic-circuits.com/555-timer/) in astable mode.

This is a simple project where you connect a buzzer to your Arduino to play a melody. You'll use Arduino's tone() function to play different tones and combine into a melody.

This is a simple Memory Game game built with Arduino. The point of the game is to repeat the sequence of colors that the Arduino comes up with. The sequence gets longer for each level. How many levels can you do?

This is a simple traffic light project that simulates the behaviour of European traffic lights: First Red. Then Red + Yellow. Then Green. Then Yellow. This repeats over and over. You can tweak the times for each stage in the code.

This project shows you how to create a simple remote-controlled on-off switch that will work with most IR remote controls. And you only need four components to build it—an IR receiver, a capacitor, a JK flip-flop, and a relay module. You can connect whatever you want to control to the relay, and then use any IR remote control to turn it on or off.

This circuit creates a light that "runs" back and forth using a 555 timer and a decade counter. It's effect is similar to the light bar on the car from the old television show Knight Rider. It's a really fun circuit to build. I once built a larger version of this for the inside of a party bus when I was a teenager. Unfortunately, I broke it the first day because I increased the voltage too much! But that's another story...