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.

Apexys

The NE555 based inductivty meter

Hi!
This blog is about my new inductivity meter based on a NE555.
For my experiments with switch mode converters, I needed a simple way to compare inductivities of coils.
Since I don't have a multimeter which can do inductivity measurement (but I have a really great multimeter, more infos perhaps in the next blog), I decided to build one.

And this is the schematic of it:

A NE555 works in its most simple rectangle osciallation configuration.
In this mode, the duty-cycle should be around 50%, but this depends on the load on pin 3.
Over the amplifying transistor Q1 the AC is given on an LC circuit.
It oscillates a freqency given by the equation:

This oscillating waves are amplified by Q2 and frequency is converted into a voltage by the RC-network of C3 and the ampmeter.
Due to the capacity of both C3 and C2 being constant, the current through the ampmeter is defined by the inductivity.
Here is a simulated image of what should happen:

Green is 100µH, blue 200µH, red 300µH and so on.
Here is a more entertaining version of it:

Well, that's the concept, let's go to the build!
Here is a image of the DPB (Drawn Circuit Board):

I had to make a capacitor bench out of the one capacitor because my supplier didn't have ceramic 10µF caps. Electrolytic capacitors are a pain in the ass and should only be used to stabilize the power supply.
 After drawing this to a piece of copper-cladded FR4 board material, I dried it using a diy-hotplate: the glass cover of a halogen desk lamp.
Now I heated up the etching solution (Sodium persulfate):

 It is the most easy way to do a board fast and with diy-methods. No big technical machinery, just a gas flame and an erlenmeyer flask.
Maybe I should have cleaned it before taking this image, but it's clean from the inside.
You can easily determine when the liquid is hot enough:
It starts to have a small layer of steam on it.

Here is a image of the board in the etching bath.
I takes about an hour on room temperature and about 20 minutes with the heating procedure.

After all the unwanted copper dissolved, I took it out of it's bath and it looked like this:

Now I used ethanol to wash of the ink.
Acetone helped me at the edges:

Well, time to get it populated!
If you are using lead-free solder, you should tin it first.
Since I'm using lead-containing solder,I had no problem soldering everything on:

The "thing" that's holding it is a third hand.
I think it is in fact the most helpful object whilst soldering.
If you don't have one, get one!
I "recycled" an old analog multimeter to get a nice µA-meter:

So, this is how it looks like with everything on it:

Now, testing time!


The inductivity used is this one:

How do you like it?
I think it's a cool little gadget, saving time and money!
You can download the LTSpice file here.
Have a good time!
apexys