Recently I had cause to make a 555 circuit on a breadboard for something else I was working on. When I was done with that I still had the circuit on a breadboard and I got thinking what if I mixed two of these with an exclusive or gate? What is here is the result of that.

## Step 1: Schematic

When I was completely finished I drew out the entire schematic of the project. It is a bit involved but I will break it down in subsequent steps.

## Step 2: Schematic Blocked Out

The whole schematic is made up of small circuit blocks. This step illustrates those.

## Step 3: Power Supply

There is a 3 terminal voltage regulator on the breadboard that supplies all power to the circuit. That regulator is supplied with unregulated low voltage direct current which I will address in the next step.

## Step 4: Raw Power Supply

I have a metal box on my desk I keep a step down transformer in. I use that reduced alternating current when I need power for my projects. Someone could use a wall wart or something to get low voltage out of. The 7085 regulator needs a couple volts over its output voltage in order to function. So anything over about 7 volts or so should do the trick. 9, or 12 volts would be great. I'll include a wider angle of my project, and a schematic of the raw side of the power supply here.

In the wider shot you can see a tan metal box in the back with black wires coming out of it going to another board with some parts on it. That is the raw side of the power supply that feeds the voltage regulator on the breadboard.

## Step 5: Astable 555 Timer

The most popular circuit of all time. It turns itself on, and off. This version is adjustable too. The smaller value capacitor you use for C1 the faster the circuit runs. Adjusting the variable potentiometer resistors R1, and R2 has an effect on circuit duty cycle as well.

What I do is I build the circuit with a large C1, say about 2.2μF, then I connect an LED to the output, and see if it blinks. If the LED blinks then I know I built the circuit properly. If I don't get any blinking then I know something is wrong. I then try to fix whatever that is.

I am providing two schematics here. It is the same circuit, just drawn differently. This circuit will be built twice for the project though.

## Step 6: Mixer

This is what I really wanted to do. I wanted to run the outputs of both 555 timers into this logic gate IC. The outputs of both 555 timers go into the inputs of a gate on the chip. The output of that gate gets fed into a preamplifier. I will cover the preamplifier in the next step.

## Step 7: Audio Preamplifier

I wanted to hear what the signal sounded like but did not feel as if the logic IC could supply enough power so I built this preamplifier for the circuit. It turns out the preamplifier itself is weak too, but it does work. I adapted this circuit from another schematic I found on the Internet, but I used a TL072 op amp as opposed to whatever that circuit called for. I imagine any single supply operational amplifier IC would work here.

This part of the circuit probably isn't even needed, but I didn't know that myself when I was building the circuit. So this step could likely be skipped. I'm including it because I built it though.

## Step 8: LM386 Audio Amplifier

Initially operating the circuit I felt I could use some more volume so I added this. It is a 50 gain LM368 amplifier and it really does boost the sound level up considerably. Again I am offering the same schematic in two different formats. Only one of these needs to be built for the project though.

## Step 9: Conclusion

I know I was brief with this article but I never know what people need to know. So if anyone has any questions please leave them in the comments and I, or someone else will try to answer them.