Random circuits

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

Speed-limit Alert

This circuit has been designed to alert the vehicle driver that he has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving.... [read more]

Symmetrical from a single voltage supply

Many times we needed symmetric voltage, but we do not have the possibility him of taking immediately, from a existing supply. Then it will be supposed him we create from the existing single.... [read more]

Self-powered Sine to Square wave Converter

This circuit is intended to provide good square waves converting a sine wave picked-up from an existing generator. Its major feature consists in the fact that no power-source is needed: thus it can be simply connected between a sine wave generator and the device under test.... [read more]

Touch Activated Light

The circuits light a 20 watt lamp when the contacts are touched and the skin resistance is about 2 Megs or less. The circuit on the left uses a power MOSFET which turns on when the voltage between the source and gate is around 6 volts. The gate of the MOSFET draws no current so the voltage on the gate will be half the supply voltage or 6 volts when the resistance across the touch contacts is equal to the fixed resistance (2 Megs) between the source and gate.... [read more]

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]

Doorbell for the Deaf

This circuit provides a delayed visual indication when a door bell switch is pressed. In addition, a DPDT switch can be moved from within the house which will light a lamp in the door bell switch. The lamp can illuminate the words "Please Wait" for anyone with walking difficulties.... [read more]