4-channel audio mixer using LM3900 IC

4 operational amplifiers, some resistors and capacitors to implement an audio mixer with a very simple design.

12 to 5 volt converter circuit (for cars)

This 12 to 5 volt converter circuit for cars is very useful. It can be used to connect 5-volt electronic devices in a car with a 12v battery. (Automotive lead-acid batteries may have a voltage of up to 13.5 volts).

Light Operated Relay Circuit using LDR.

The LDR varies its value (ohms) depending on the amount of light that illuminates it. The more light less resistance and less light more resistance, The level of light that makes the relay activated is adjusted to the desired value with a potentiometer.

12V Auto Turn-off Battery Charger

This 12V Auto Turn-off Battery Charger with current limiter, uses only 4 transistors, will stop charging the battery when it has 14 volts between its terminals and limits the charging current to a maximum of 2 amps.

Car Burglar Alarm using two 555 timers

This is a simple Car Burglar Alarm circuit that uses a dual contact relay and two 555 timers, each of them working as a monostable multivibrator.

The alarm will activate the car horn, approximately 5 seconds after either door is opened and has not been properly closed.

This temperature to voltage converter circuit, convert the sensed temperature by a thermistor into a voltage level.

The circuit achieves an acceptable performance between 0 and 24°C

Delayed activation 15V voltage source using LM317.

This circuit uses the LM317 voltage regulator. This voltage source also uses a bipolar PNP transistor and an electrolytic capacitor, to achieve a delayed activation of the voltage regulator

This simple humidity sensor circuit using a 555 timer, shows us the humidity level that a ground under test has. To achieve the goal, a couple of probes are used.

These probes are placed on the ground to be tested.

6-LED VU meter using one transistor

This simple 6-LED VU meter allows us to visualize the level of an audio signal. Due to its few components, it is a cheap circuit and easy to build. The components are very common and very easy to obtain.

This clock signal generator using 7400 IC, is an astable circuit which uses the TTL 7400 integrated circuit.

The 7400 IC has four 2 inputs NAND gates (NOT AND). We only use two gates of this integrated circuit.

Logic Probe using NOT Gates (Inverters)

This logic probe using NOT Gates is implemented with three NOT gates, one rectifier diode, two LEDs and two resistors.

Dimmer / AC motor speed controller

If you want to control the light level of a room or if you want to control the speed of a drill or a fan (devices that use AC motors), this is the circuit you are looking for