Random circuits

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

LED Tester Circuit Diagram

You have to admit that these tiny electronic lamps are handy, and they last almost forever. Around 40 years after Nick Holanyak developed the first LED, they have become just about indispensable. Any self-respecting electronics hobbyist always has a few in his junk box. But before you use LEDs, it’s a good idea to check them out. With a LED tester, you can even do it in the dark!... [read more]

Crystal Tester

This circuit enables you to test quartz resonators at the range values from 32kHz to 24MHz. Confirmation of good state of quartz resonator is done by diode signalling LED and acoustic signal... [read more]

Sunrise Lamp

In this circuit, a 120VAC lamp is slowly illuminated over a approximate 20 minute period. The bridge rectifier supplies 120 DC to the MOSFET and 60 watt lamp. A 6.2K, 5 watt resistor and zener diode is used to drop the voltage to 12 volts DC for the circuit power. The bridge rectifier should be rated at 200 volts and 5 amps or more. In operation, a 700 Hz triangle waveform is generated at pin 1 of the LM324 and a slow rising voltage is obtained at pin 8.... [read more]

Set/Reset Flip Flop

This is an example of a set/reset flip flop using discrete components. When power is applied, only one of the transistors will conduct causing the other to remain off. The conducting transistor can be turned off by grounding it's base through the push button which causes the collector voltage to rise and turn on the opposite transistor.... [read more]

Transformerless Power Supply

This supply uses no heavy step down transformer and has an extremely low parts count. The circuit can be built very small and can supply small currents for small projects. The major downfall of this supply is that it is not isolated from the AC line and can only supply small currents.... [read more]

High Current MOSFET Toggle Switch with Debounced Push Button.

It is useful where the load needs to be switched on from one location and switched off from another. Any number of momentary (N/O) switches or push buttons can be connected in parallel.... [read more]