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10 september 2011

Op Amp experiments I

Op Amp Experiments (necessities):

I been dabbling in electronics for a little while now, and of course I used Op Amps in a few circuits. A lot of those circuits were adaptations from what I found in books and datasheets.

However, I never fully understood how things worked.

So I set myself the goal to get a better understanding of Op Amps. What can you do with them, and how. Back to basic!

Also I decided to do these experiments with as few parts as possible. For the Op Amp I choice the lm358, readily available and cheap (and I had some laying around). A breadboard, wires, a few potmeter, some capacitors of different standaard values and some other knickknacks.

I use a DSO nano and cheap multimeters to measure things.

A while back I made myself a function generator from a xr2206 which I use for signal generation.

There is a little audio amplifier build into the function generator (well the function generator is build into the audio amplifier). I based mine of a circuit I found in an Elektor magazine from the ‘70’s (could be ‘80’s), but here you can find something similar.

SparkFun used to sell a xr2206 kit, but it’s retired now. The one I build is a little more involved. I can choose between DC offset or not and I can manipulate the symmetry and amplitude of the waves. Don’t have schematics laying around anymore but if I find them I will post. To be honest the xr2206 isn’t the easiest thing to find.

Maybe it’s time for someone to design a cheap and useful function generator kit based on more modern techniques.

One of the first things I want to explore is the use of positive voltage, negative voltage, ground and virtual ground with Op Amps. I always seem to screw that up when designing a circuit.

To do this I first needed a power supply that could deliver positive voltage, negative voltage and ground.

I found this nifty little circuit based on a 555 timer that could deliver just what I needed. It works well with a 12 volt DC walwart.

I found this circuit on my computer in a folder with hunderds of circuits. I unfortunately don’t know who the designer was. I believe I got it from somewhere. I just added a 7812 volt regulator to it on my prefboarded circuit.

The first experiment will be “How to amplify a sinusoidal signal with no DC offset (aka audio signal)”

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