Car battery monitor circuit using 4 LEDs

This simple Car battery monitor, allow us to know the voltage of the battery at all times. To achieve this 4 leds are placed somewhere on the dash of the car. Each LED has a label indicating the battery voltage at that time.

This 2 LED Temperature change indicator shows us, by means of two LEDs, when the sensed temperature is above or below a set limit.

When the temperature is above the pre-set temperature level, LED D1 will light up and if it is below, LED D2 will light up.

12V Power Supply using Zener and 741 Op. Amp.

This 12V Power Supply has, as its main characteristic, a low output impedance. This is a very desirable feature in voltage sources and is achieved with a large open loop gain that the operational amplifier has.

Microphone Mixer using operational amplifiers

This Microphone Mixer combines signals from 3 different sources (3 microphones) easily and economically.

Variable voltage regulator using 7805 and 741.

Very simple variable voltage regulator with very few components. Output Voltage from 5 to 30 volts

Op Amp Tester Circuit Diagram

Very simple circuit to test 741 op amp or another IC with the same pin configuration. Circuit working explanation

Shadow detector alarm circuit with two LDRs

This circuit detects if there is a difference of lighting between two LDRs, and sends an audible and visual warning. Circuits that use two LDRs are more reliable than those that use only one.

Electronic sound control circuit (applause)

This electronic sound control circuit works like a sound activated relay and can activate or deactivate a device connected to it, by two consecutive claps.

Twilight switch circuit with Op. Amp.and LDR

This Twilight switch circuit activates a light, a lamp, a motor, etc., at the time of sunset and performs the reverse process at dawn.

This is an ideal circuit for activating a security light that must be on all night.

This 12v battery charger circuit using a LM350 and LM301A op-amp.

This 12v battery charger circuit allows you to charge a 12-volt car battery using a LM350 voltage regulator and a LM301A operational amplifier.

Temperature alarm circuit with 741 operational amplifier

This temperature alarm circuit with operational amplifier activates a relay when the temperature of the place to be controlled exceeds a set level. Useful for an oven temperature control or a cooling system

This continuity tester using 741 operational amplifier, operates as a differential amplifier.

A good application for this circuit would be to test welds made on a printed circuit board. It could be also used to test continuity of wires, connections, etc.