Random circuits

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

Temperature-controlled Fan

This circuit adopt a rather old design technique as its purpose is to vary the speed of a fan related to temperature with a minimum parts counting and avoiding the use of special-purpose ICs, often difficult to obtain.... [read more]

Ultra-simple Voltage Probe

This circuit is not a novelty, but it proved so useful, simple and cheap that it's worth building.... [read more]

Adjustable Current Limit For Dual Power Supply

This current-limiting circuit, shown in this example as part of a small bench power supply, could in principle be used in conjunction with any dual-rail current source. The part of the circuit to the left of the diagram limits the current at the input to the dual voltage regulator (IC4 to IC7) so that it is safely protected against overload. The circuit shown produces outputs at ±15 V and ±5V. The voltage regulators at the outputs (7815/7805 and 7915/7905) need no further comment; but the current-limiting circuit itself, built around an LM317 and an LM337, is not quite so self-explanatory.... [read more]

Simple but reliable car battery tester

This circuit uses the popular and easy to find LM3914 IC. This IC is very simple to drive, needs no voltage regulators (it has a built in voltage regulator) and can be powered from almost every source.... [read more]

3-30V 3A Adjustable Regulated DC Power Supply

This power supply is meant as an auxiliary or as a permanent power supply for all common circuits based on a stabilized DC voltage between 3 and 30V provided that the consumption does not exceed 3A. Of course this power supply unit can also be used for other purposes. Be replacing the trimmer by a potentiometer, it may even be used as an adjustable power supply unit. A good quality heatsink must be used.... [read more]

Whistle Responder Schematic - Circuit Diagram

This device beeps intermittently for about two seconds when a person in a range of around 10 meters emits a whistle. The first two inverters contained in IC1 are used as audio amplifiers. IC1A amplifies consistently the signal picked-up by the small electret-microphone and IC1B acts as a band-pass filter, its frequency being centered at about 1.8KHz. The filter is required in order to select a specific frequency, the whistle's one, stopping other frequencies that would cause undesired beeper operation. IC1C is wired as a Schmitt trigger, squaring the incoming audio signal. IC1D is a 2 second-delay monostable driving the astable formed by IC1E & IC1F. This oscillator generates a 3 to 5Hz square wave feeding Q1 and BZ1, thus providing intermittent beeper operation.... [read more]