Random circuits

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

Courtesy Light

This circuit is intended to let the user turn off a lamp by means of a switch placed far from bed, allowing him enough time to lie down before the lamp really switches off. Obviously, users will be able to find different applications for this circuit in order to suit their needs.... [read more]

Repeating Timer No6

This circuit is the opposite of Repeating Timer No.5. It will only begin to operate if the temperature falls below the preset level. Again - the variable resistor (preset) lets you choose the temperature below which the timer will function.... [read more]

Opamp VHF FM Transmitter

ICs that in the past were far too expensive for the hobbyist tend to be more favourably priced these days. An example of this is the AD8099 from Analog Devices. This opamp is available for only a few pounds. The AD8099 is a very fast opamp (1600 V/ms) and has high-impedance inputs with low input capacitance. The bandwidth of the opamp is so large that at 100 MHz it still has a gain of nearly 40. This means that this opamp can be used to create an RC oscillator. The circuit presented here realises that.... [read more]

Speaker Box Audio Amp

After buying the processor, monitor, and printer, I wasn't willing to spring for a set of speakers too. After going "soundless", I decided to add speakers. Of course, this was the perfect excuse warm up the soldering iron to try out a new design. This original design is a variation on a well-known design, examples of which can be found in a great many texts.... [read more]

3.6 Volt cell phone battery meter

This is a similar circuit to the above and provides a 4 LED bar graph indicating the voltage of a common 3.6 volt Lithium - Ion recharable cell phone battery. The reference voltage is provided by a TL431 programmable voltage source which is set to 3.9 volts where the TL431 connects to the 1K resistor. The lower reference for the LED at pin 14 is set with the 5K adjustable resistor.... [read more]

5V Regulated Power Supply Circuit Diagram

This circuit is a small +5V power supply, which is useful when experimenting with digital electronics. Small inexpensive wall tranformers with variable output voltage are available from any electronics shop and supermarket. Those transformers are easily available, but usually their voltage regulation is very poor, which makes then not very usable for digital circuit experimenter unless a better regulation can be achieved in some way.... [read more]