# Using LM386 As an Oscillator.

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## Introduction: Using LM386 As an Oscillator.

Most people know the LM386 as a mono amplifier. What may surprise some people is that the LM386 can also be easily converted into an oscillator without any other specific IC's like the common 555 timer chip.

In this Instructable, I'm going to provide a straight-forward schematic and some brief explanations as to how this will work and also some ideas as to what kind of tinkering you can do with this device.

## Step 1: Components List

LM386 Amplifying IC

Resistors
1k Ohm
10k Ohm
100 Ohm
100k Ohm*

*This resistor can vary between 10k Ohm and 100 k Ohm but other pots (200k or 1M) sound really nice.

Capacitors
470 microFarad Polarized (I prefer something lower than 100 microFarads and I strongly suggest using a 50 microFarad capacitor).

*This capacitor can vary between 0.01 microFarads and 0.27 microFarads. I noticed that  using a 0.1 microFarad capacitor gets extremely close to a square wave.

Misc.
8 Ohm Speaker
9 volt Battery
9 volt Connector

## Step 2: Schematic

This requires only a few components.

The LM386 has a built in feedback resistor (1350 K Ohms) to account for the likelihood that you will use a battery for your projects. By connecting Pin 1 and 8 together, you are bypassing this resistor.

Pin 7 doesn't connect anywhere.

Pin 6 connects to the 9 volt battery.

Pin 4 connects to the ground

As seen in the first picture, the Red X's indicate that there is no connection. So Pin 2 and 3 do not connect, and Pin 2 and 4 do not connect. The rest should be pretty straight forward.

The second picture is an earlier schematic. It is the same but has a few more notes. Rt and Ct indicate that these components can vary. By changing these components you can effect the Frequency being generated.

A simple equation (or so I heard) to determine the Frequency in Hertz is (2.5)/(Rt * Ct). Rt will be between 10,000 and 100,000 Ohms.

If R3 (100 Ohm) is left out or removed, you will get a loud squeal so try to avoid that.

## Step 3: Things to Try

You can insert a volume knob by placing a Variable Resistor in series with the 8 Ohm Speaker. Keep it less than 500 Ohms. I tried this with a 1k Ohm variable resistor and it didn't really work well.

Replace Rt with a PhotoCell to create a Solar theramin type device.

I'm not sure about this but with a 470 microFarad capacitor, I get loud clicks/tapping sounds rather than a tone (maybe I just made a mistake). I fixed this by using much smaller capacitors. I noticed that anything bigger than 100 microFarads sounds like a purring cat but anything smaller sounds like a real tone.

## Step 4: Conclusion

With the LM386, I was able to make a tiny solar theramin which I mounted on a 1 inch by 1.5 inch PCB board. I replaced the 8 Ohm speaker with a 1/8 inch headphone jack. I replaced Rt with a Photocell.

The great thing about this is that it doesn't drain the power of a 9 volt battery. With other projects, the 9 volt drained in a day.

## Step 5: Square Wave

The previous schematic I posted wasn't exactly a square wave, so I made a few changes and experimented with the sound.

The schematic posted in the images should give you a square wave oscillation.

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## Questions

Maybe I have cheap/weak parts but, I've tried this build 3 times and each time I smoke the lm386. Where have I gone wrong? Please help! Thanks in advance

This is an old instructable, but for you and anyone else reading this, there's an error in the schematic. The pins aren't labeled on the diagram, but on most LM386es the second pin down from the top left is the inverting input, and the third pin down is the non-inverting input.

The top of the timing capacitor network needs to be connected to the inverting input (-), and the feedback resistors need to be connected to the non-inverting input (+), not the other way around as they are in the diagram.

Great tutorial.

I put one of these together it was a pretty quick build. I have never tried turning an opamp into an oscillator and this has definitely given me some ideas. I found this www.calvin.edu/~pribeiro/courses/engr332/Handouts/oscillators.pdf neat little page made by texas instruments. It outlines a circuit similar to this one and then explains how to stabilize the wave and also goes on to give instructions on how to build other oscillators with different waves shapes. This was a pretty fun toy for a while so thank you aDimWit for getting me interested and posting this.

Designers work hard to prevent thier amplifiers from becomming oscillators.  So you come along and show them how wrong thery are.  Nice work. ( just kidding ) Nice work, really

åww; is it really just a square wave?  I've sort of been hoping that high-power audio amplifiers might be configured as oscillators and used to drive the primaries of step-up transformers for making HV supplies, easier and perhaps more efficiently than the usual 555+power transistor setups.  After all, a 10W amplifier chip (pretty readily available, and cheap on the surplus market) ought to be good for putting 10W of power through a transformer, with a lot more protections and such than the usual circuit...

Using an amplifier as an oscillator should not be too surprising, since an oscillator is basically an amplifier that feeds some of its output to itself as input, setting up oscillations.  I am sure your Instructable will be helpful to anyone who has not thought of the similarity and wants to make use of it.