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:
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):
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):
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.
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:
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!