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 loading of the C1 keeps the coil closed and additionally it is also consumed by D1 and R1.

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.


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 the load will be handled by a secondary relay that will oscillate as a function of the frequency of C1 and the resistance value of Relay 2.

In this circuit add another relay in order to stabilize the pulse frequency for the load. Then with this arrangement, the frequency no longer depends on what you connect to the output of the oscillator. We will always have the same pulse frequency, which results in a more stable 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.

Relay 2 can also be placed in a double polarity arrangement so that the negative and positive pulse is obtained at the output.

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.

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.

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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