Sound-emitting Oscillator With a Variable Tini Foil Capacitor

Hello everyone, I hope you like this instructable about tinfoil. Any doubt, comment or correction will be well received.

We are going to make a really big capacitor, and we will use it in a circuit that emits sounds of different frequencies (because it will be a variable capacitor). Let´s start!

What do we need?

• LM324 Operational Amplifier
• 3 resistances of 10k
• 1 resistance of 1M (it could variate if your plates doesn't measure 1.5nF aprox)
• cable and wire
• scissors and glue
• contact paper
• tinfoil (at least 6m*35cm)
• Cardboard (it could be a pizza box, as I did)
• 1 protoboard
• a 12V or 18 V power supply (i recommend 18V)
• a buzzer (piezoelectric)
• multimeter with capacitance-meter

To avoid problems with the resistance of 1M, in step 3 i will let you how to calculate it.

To do this step, we need the cardboard (the pizza boxes), contact paper, tinfoil, scissors, glue, and cable, and if you want to measure the capacitance, the multimeter.

[Picture 1 and 2]: We will put in the box the necessary tinfoil to cover all of it. Make sure that all the tinfoil is in contact with the other pieces (this, so that the plate will be the same conductor). We can put some glue so that the tinfoil doesn't move.

[Picture 3]: Then, we will cover all of it with the contact paper, so that, when bringing both plates closer together, they do not touch (if they did touch, it would no longer be a capacitor, since we need a dielectric, or rather, an insulator between both plates)

[Picture 4 and 5]: When you have finished both, you are able to put one cable in contact with each plate (the only requirement is that the cable touches the aluminium).

[Picture 6]: Once you have put the cable to each plate, we are ready, we have our new Capacitor.

But... How do we need it´s capacitance? with the multimeter. We need to put the plates in a stable place, one on top of the other as you can see in the Picture 7. We connect the multimeter to the wires and select to measure capacitance (Picture 8), and then, we know the capacitance.

Let´s go to the next step.

In this step, we need: LM324, 3 resistances of 10k, 1 resistance of 1M, the buzzer (or piezoelectric), protoboard, the power supply, multimeter, and the capacitor we made in step 1.

NOTE: if your capacitor doesn´t measure 1.5nF, maybe you will need another value, but don't worry, in next step I will show you how to find the correct value

We need to assemble the components on the protoboard, as it appears in the schematic.

Once you assemble it, you just need to use your power supply and put in pin 4 the positive cable, and in pin 11, put the ground of your power supply (as you can see in the schematic).

The second picture is the assembled circuit.

In the left inputs (where it says "Capacitor"), there will be the cables of the plates you did in step 1, you need to connect it here. Be sure the plates are as I mentioned in the step 2 (in a stable place).

So, when you have connected all, you will hear the sound if it is in a range of 20 to 20,000 Hz (if not, it will be for the capacitance). If you don't hear nothing (or if the sound does not like you), go to step 3 to correct the frequency you hear.

If you separate one plate from another, the sound must change (the frequency will increment).

If you have problems with the sound, you need to re-calculate R_f

Let's suppose that now we want a higher sound, that is, at 1000Hz, and that our capacitance on the plates we made was 0.2nF, and if we separated them, we could measure up to 0.02nF. So, we need to calculate with the higher value of capacitance:
f=1000

C=0.2*10^-9

if we calculate with the equation in the picture, we have:

R_f=1/(1.386*1000*0.2*10^-9)

R_f=3607503.6075

R_f=3.6*10^6

R_f=3.6M ohms

We obtain 3.6M with these capacitance and frequency.

So, R_f=3.6M

Go see the video from minute 5:30, and ENJOY!