Random circuits

Here are some of over 800 projects from our free circuit diagrams database. For more, try browsing categories menu on the left.

Park Aid

This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm.... [read more]

Transformerless 5 Volt Power Supply

An increasing number of appliances draw a very small current from the power supply. If you need to design a mains powered device, you could generally choose between a linear and a switch-mode power supply. However, what if the appliance’s total power consumption is very small? Transformer-based power supplies are bulky, while the switchers are generally made to provide greater current output, with a significant increase in complexity, problems involving PCB layout and, inherently, reduced reliability.... [read more]

IR Remote Control Tester

This small circuit is ideal for checking the basic operation of an infrared remote control unit. The circuit is based on the brilliantly simple idea of connecting a piezo buzzer directly to an IR receiver IC. This method is almost as simple as connecting a photodiode directly to the input of an oscilloscope, but has the advantage that no oscilloscope is needed: the compact unit is always ready to use and much easier to carry around than bulky test equipment.... [read more]

2Watt Audio Amplifier

This amplifier was designed to be self-contained in a small loudspeaker box. It can be feed by Walkman, Mini-Disc, iPod and CD players, computers and similar devices fitted with line or headphone output. Of course, in most cases you will have to make two boxes to obtain stereo.... [read more]

Automatic Low-Power Emergancy Light

Here is a white-LED-based emergency light that offers the following advantages. 1-It is highly bright due to the use of white LEDs. 2-The light turns on automatically when mains supply fails, and turns off when mains power resumes. 3-It has its own battery charger. When the battery is fully charged, charging stops automatically. The charger power supply section is built around 3-terminal adjustable regulator IC LM317 (IC1), while the LED driver section is built around transistor BD140 (Q2).... [read more]

Components Voltage Tester Circuit Schematic

This simple circuit tests speakers, microphones, transformers and voltage. It's basically a very low frequency oscillator that produces extremely short 'fruity' pulses. The type of sound produced is very easy to hear and to determine the precise direction it is coming from, thus making it ideal for checking the phasing in multiple speaker installations. It is also very useful for car stereo installations as well as public address systems where it can drive dozens of speakers directly on a 100V or 70V line system.... [read more]