Como hacer un oscilador casero

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How to assemble a homemade oscillator or simple pulse generator with relays. Easy to assemble and well explained with their diagrams.

How to make a home oscillator

For many things, especially in mechanics, it is necessary to use some type of pulsating circuit that we can regulate to put signals to lamps, coils, injectors among other things. In this article I will tell you then how to make an oscillator with easy-to-acquire components and with few elements:

The first of all:

The oscillator with relay:

Or pulse generator to relay. It is very common to see this circuit on the internet:

oscilador casero usando un relé

The relay has two contacts, one normally open and the other normally closed. The load to be fed is usually connected to the NO contact of the relay, which gives the greatest amount of pulse time. The frequency is given by the values ​​of C1 and the load that in this case is D1 and R1 in series. Increasing the values ​​of C1 we obtain lower frequency.

The recommended values ​​are between 100uF and 2000uF.


- R1: 690 ohm.

- D1: Led diode.

- 12V relay with two contacts.

- C1: electrolytic capacitor of more than 300 uF.

Operation and analysis of the circuit:

In this case the circuit will operate as seen in the following image:

oscilador de relé funcionando

1.- When the circuit is energized by closing the button, the relay is activated and capacitor C1 is also charged.

2 .- At this time there is a slight delay framed in the time it takes the C1 to load, then most will go through C1 instead of the coil.

3.- When C1 is loaded, current flows through the relay coil and the contact is activated, leaving the relay coil again without a negative supply.

4.- At this moment the load of the C1 keeps the coil closed, consuming its energy.

5.- When the load of C1 is consumed, the relay changes state again and the cycle is restarted.

As you can see, the frequency is given by C1 and the resistance that we have connected to the normally open contact of the relay. So we do not have a stable frequency because it depends on what we connect there.

High voltage transients

You can check the existence of high voltage transients by mounting the following assembly:

oscilador de rele con transitorios de bobina

The additional thing is:

D2: Rectifying diode 1N4007

C2: Electrolytic capacitor 20uF 250V.

Remember to be very careful when handling the charged capacitor. Causes dangerous electric shocks. If the capacitor is more than 20 uF They can be deadly.

The operation of the circuit is simple, as there is no longer C1 (it is open), a phenomenon of high voltage transients inverse to the current occurs in the coil. They pass to the capacitor C2 by means of D2 that leaves them retained so that they do not reach the rest of the circuit.


To solve this situation I propose the following circuit:

Proposed Relay Oscillator:

mejora al oscilador de rele por chica mecanica

Like the previous circuit, it operates in the same way to generate the pulses, except that in this case a complete square wave will be produced in the output load, which will be handled by a secondary relay that will oscillate as a function of the frequency of C1 and the resistance value of Rele 2.

In this circuit add another relay in order to stabilize the pulse frequency for the load. For this, we can stabilize the + 12V voltage of relay 1 (RL1) with some regulator such as 7812, and independently power relay 2 (RL2). Then we will always have the same pulse frequency.

The other particular thing in this circuit, is the way of connection of the relay 2, placed in a double polarity arrangement, to the output we will obtain a complete square wave, which results in a more stable and better designed oscillator.

I added the diodes D2 and D3 to avoid the internal surges produced in the coils of the relays when the contacts operate. The surges if not handled well, shorten the useful life of the capacitor and inserts noise to all circuits that connect to that system. In some cases this noise is deadly. So you have to be very careful with these.

Another proposed circuit to generate pulses with relays:

oscilador de rele con pulsos iguales

For this oscillator two relays are needed as the previous one that I proposed, except that with this a symmetrical pulse is produced; that is, our oscillator has the same operating cycles in both the off and the on.

Its operation is simple:


When we close the switch, the relay RL1 is off and its NC contact passes energy to the relay RL2 by actuating it.

When RL2 is activated, RL1 is activated, leaving RL2 consuming the energy of capacitor C2.

When C2 is completely discharged, RL2 is opened, it is at this moment that RL1 is activated with the load that C1 has. Leaving RL2 without tension and in the same resting position.

Once C1 is discharged, RL1 is deactivated and re-energized to RL2. Restarting the cycle in this way.

Another symmetric relay oscillator with transistor

This design is much more stable than the previous one and also more economical. I show it below:

oscilador de rele con pulsos iguales con transistor


 - R1: 690 ohm.

 - R3: 20k ohm.

 - R2: 10k ohm.

 - D2: Led diode.

 - D1: Rectifier diode 1N4007

 - 12V relay with two contacts.

 - Q1: Transistor NPN 2N2222

 - C1: electrolytic capacitor of more than 1 uF.

This circuit is a variant of the previous symmetric of two relays. The interesting thing about this proposal is that it uses a smaller and cheaper capacitor, just like the auxiliary relay is removed and replaced by an NPN transistor.

As always in my analysis I offer the advantages and disadvantages of the proposed circuits. Most of all for this one that is simple and quite popular, so I'll list them for you to see them.

Advantages of the relay oscillator:

1.- Very simple to use. Anyone with basic knowledge of electricity can assemble it without any difficulty.

2.- Economic to manufacture.

3.- High output current.

4.- Excellent electrical insulation by the use of contacts. Excellent for producing high power sparks in coils, much higher than that achieved with a transistor.

Disadvantages of the Relay Oscillator

1.- Frequency of operation limited and a little unstable.

2.- Pulses of irregular duration. The ignition cycle is much longer than the off cycle. (For the initial circuits)

3.- If you do not place the diodes in the relay coil, dangerous overvoltage and high frequency peaks are generated. It is not safe to connect it together with electronic equipment. Connecting it to the battery of the car with all the electronic elements of it would be very risky.


Uses of the Relay Oscillator

In the field of electronics:

There are many applications taking into account the diode in the coils of the relays.

In the automotive field:

It can be used as:

- Warning flashing light.

- Activation signal for windshield wipers.

- Coil tester.

- Injector tester, but only for small periods of time.

Remember that the opening pulse is very long and reheats it.

Video how i do it

Questions or suggestions

In the box below questions.

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Written by:

Dennis García




Muy básico y sencillos de armas estos osciladores a relé.

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    Como hacer un oscilador casero

    Como hacer un oscilador casero

    How to assemble a homemade oscillator or simple pulse generator with relays. Easy to assemble and well explained with their diagrams.

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    4 Question(s) answered

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    • Asked by Luis
      on 03/24/2019
      Hola necesito que sea más específico con el diagrama lo armó como pero no me funciona gracias. Answer:
      Luis, todos tienen sus simbolos y valores en la tabla. Los probé y monte todos para verificarlos. En mi video arme el 1ero y el último. ¿Cual es el que no puedes montar?
    • Asked by Victor
      on 03/25/2019
      Que tal chica mecánica un gran saludo desde México. tengo una pregunta en el último oscilador el relé tendría que ser de 12 voltios. pues si sé pone de 5 o 6 voltios hay probabilidad de que se pueda quemar. porque está conectado a los 12 voltios. sería tan amable de aclararme ésta duda y gracias por compartir. Answer:
      Que tal Victor, los resistores de base del transistor son muy altos, y no lo ponen a trabajar en saturación (a plena corriente), sino como amplificador. So colocas un relé de 12V no se acciona. Si colocas un arreglo de transistores en darlington si es posible colocar un relé de 12V.
    • Asked by Eden proño
      on 03/25/2019
      Dennis mucho gusto de ver tus vídeos te pregunto algo estoy fabricando un probador de inyectores osea un banco de prueba y quisiera Aser el circuito pero nesesito tú experiencia que me ayude de manera sencilla para poner los 4 inyectores a funcionar acuérdate que ay que aselerar y desminuir el motor será que me puedes ayudar grasias mi nombre es eden grasias Answer:
      Eden, puedes escribirme por mi instagram, o por el correo con atencion a Chica mecanica o Dennis. Y con gusto te ayudo en lo que pueda.
    • Asked by Flavio Biaggini Véliz
      on 04/18/2019
      Hola, que tal, necesito realizar un generador de pulso, pero para accionar un solenoide de 105 volt, me podrias ayudar con que elementos lo puedo armar?? saludos desde Iquique, Chile Answer:
      Flavio. Puedes escribirme a con todas los requerimientos y dudas y con gusto te ayudo. Es decir, frecuencias, ¿104V AC o DC? ese tipo de cosas.

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