4-channel audio mixer using LM3900 IC

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

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

Differential Temperature Controller.

This circuit measures the temperature difference between 2 sensors and activates a relay when they are different

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

Over-temperature alarm using operational amplifier.

This over-temperature alarm circuit uses a common semiconductor diode as a temperature sensing element.

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.

Inverting Summing Amplifier using Op Amp

The inverting summing amplifier using op amp outputs a voltage equal to the sum of the voltages it has in its inputs. The following explanation is based on an adder of three inputs, but applies to an adder of any number of inputs

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.

This High – Low Temperature 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.

1 Input – 4 Outputs Stereo Audio Splitter

This 1 Input – 4 Outputs Stereo Audio Splitter has a single input and 4 independent outputs, each amplified with an operational amplifier.

Each operational amplifier is configured as an emitter follower, to take advantage of its high input impedance and low output impedance, thus avoiding distortion in sound.

An oscillator circuit can have many applications.

The diagram shows how to make it work as a light sensitive sound generator using a LDR and a 741 operactional amplifier

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

This mixer can even work as an amplifier and portable mixer because of its few components.