Random circuits

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

Fridge-Door Open Alarm Circuit Project

It beeps if the fridge door is left open for too long or hasn't closed properly, to stop food from spoiling. There are lots of other uses as well. A refrigerator or freezer door that is left open or ajar may cause the food contents to spoil. In some cases, the internal temperature of the fridge or freezer will be maintained if the refrigeration system can cope with the open door.... [read more]

Bicycle Back Safety Light Circuit Schematic

This circuit has been designed to provide a clearly visible light, formed by 13 high efficiency flashing LEDs arranged in a pseudo-rotating order. Due to low voltage, low drain battery operation and small size, the device is suitable for mounting on bicycles as a back light, or to put on by jogger/walkers. IC1 is a CMos version of the 555 IC wired as an astable multivibrator generating a 50% duty-cycle square wave at about 4Hz frequency.... [read more]

12V Dimmer

A dimmer is quite unusual in a caravan or on a boat. Here we describe how you can make one. So if you would like to be able to adjust the mood when you’re entertaining friends and acquaintances, then this circuit enables you to do so. Designing a dimmer for 12 V is tricky business. The dimmers you find in your home are designed to operate from an AC voltage and use this AC voltage as a fundamental characteristic for their operation. Because we now have to start with 12 V DC, we have to generate the AC voltage ourselves.... [read more]

Battery Indicator Circuit For The Caravan

This i-TRIXX circuit can prevent a whole lot of trouble for those of you who go on holiday in a caravan. It would be a significant damper on your holiday spirit when you are ready to leave the camping and discover that you have used your battery too much and that you are now unable to start the car. This annoyance can be avoided if you were warned early enough by an illuminated LED when the charge in the battery threatens to become too low.... [read more]

DC or AC Voltage Indicator Circuit

This circuit is not a novelty, but it proved so useful, simple and cheap that it is worth building. When the positive (Red) probe is connected to a DC positive voltage and the Black probe to the negative, the Red LED will illuminate. Reversing polarities the Green LED will illuminate. Connecting the probes to an AC source both LEDs will go on.... [read more]

Bistable Flip Flop

Here are two examples of bistable flip flops which can be toggled between states with a single push button. When the button is pressed, the capacitor connected to the base of the conducting transistor will charge to a slightly higher voltage. When the button is released, the same capacitor will discharge back to the previous voltage causing the transistor to turn off.... [read more]