Sunday, February 27, 2011

The NE556 based Theremin

This is my second entry for the 555 contest.

It is the famous instrument, the theremin in a 556-based version.
I had to overclock the timer to about 4Mhz and it works!
This is pretty cool since the timer has a maximum frequency of about  200kHz.
This is the schematic:

The two 555 cores of the NE556 work both as rectangle oszillators.
The frequency of the second one is altered by my body frequency.
Now both signals are mixed in the middle and amplified via Q1.
An earplug makes it hearable.

This is what the signal looks like:

It is basically HF with some NF modulated on it. AM. Like in the radio.
In LTSpiceIV, you can simulate a sound output and play it in real life!
Simply add the SPICE directive .wave C:\waveout.wav 16 44100 V(n010) to your simulation file.
What it does is:
It generates a .wav-file with 16 bit resolution and 44,1kHz samplerate in C:\waveout.wav that sounds exactly like the voltage on node 10.
Here is a sound example of this schematic.

Now, I etched a DCB in my standard procedure.

The lower pad left is the pad to put your hand on. Then move the other hand over the big upper ground plane.
Resistors were the first parts to be populated.

Now the timing caps followed.
At first, I wanted to use 1206 54pF caps but they didn't fit. Well, the dangers of a self drawn board I assume. As a replacement, two 20pF caps in 0805 on every side came to the rescue.
The two bars on the right side act as a cap bench. I do this on lot of my circuits: First I just solder in a 100nF ceramic capacitor and if it is not sufficient, I solder in other caps. In this particular case, I soldered in quite a few caps. Starting from the upper border: 270pF x2, 100nF x2, 800nF x2, 1µF.

After having done this, some silicon followed:

Then the NE556 and some other stuff and it's all ready to use!

It is really difficult to play specified tones on this thing.
I end up most of the times getting WEEEH-UUUUH-WEEEEH-UUUUUH sounds.
But hey, it works!
Here is a prove:

What do you think of it?
As usual, you can download the simulation file here.


1 comment:

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