Refrigerator door alarm circuit with two 555 timers

This refrigerator door alarm circuit alerts you when the door has been left open. Very important, because the power consumption increases when this happends. It uses the popular 555 timer IC

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.

Tone generator using two 555 timers

This circuit uses the well-known 555 integrated circuit to generate a range of sounds that are heard through a small loudspeaker.

Water level controller circuit using CD4001

This water level controller circuit controls the level of water in a tank. Unlike mechanical controls using a floating buoy, this circuit uses two sensors, an upper sensor and a lower sensor,

Audio level indicator circuit using LM339

This audio level indicator is very interesting because it allows us to visualize the audio level intensity by connecting this circuit to the input of a loudspeaker.

Rain detector using two transistors

Rain detector using two transistors. Circuit that aims to alert the beginning of the rainfall. Its few components make it an interesting and easy project.

Surge Protection Circuit (Voltage Delay Circuit)

This Surge protection circuit is placed between the DC voltage source and the circuit that you want to power. This circuit delays the voltage given by the power source and allows the voltage to be applied to the circuit or device a few moments later.

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.

Dark detector circuit using LDR and relay

This circuit uses, as a main component, an LDR (photoresistor). An LDR changes its resistance value depending on the amount of light it received. The more light means less resistance, the less light means more resistance.

Microphone Mixer using operational amplifiers

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

Doorbell for Deaf People.

When a deaf person is alone in a house, it would be very difficult to realize that someone is knocking on the door without any visual warning signal.

Inverter for fluorescent lamps (12V to 120 / 220 VAC)

Simple circuit using the 555 timer, a transformer and a transistor Useful to use with a car battery.