Backyard Aquaponics
A place to discuss aquaponics

While working on my DIY PIC Scope I found I needed a programmable gain Op Amp.
They are available but generally more expensive and harder to get (here) than standard Op Amps.

I was sent a circuit by a mate to make any old Op Amp "programmable"



R2-R5 are connected to digital pins on the micro.
To turn a stage on, make the pin an output and drive it to 0V
To turn it off, make it a high impedance input (on PICS watch the internal pull-up resistors on some ports, make sure they are disabled)

Brilliantly simple, and very effective, wish I'd thought of it !

I think only people who graduate from electrical engineering can understand that.

Well, maybe.
But I build circuits I don't fully understand, following someone else's diagram.

This one is pretty simple.
Any understanding of the gain stage of an OpAmp will make this circuit pretty obvious.

More than happy to explain, if anyone needs an explanation

Nobody need explanation on this, i think.
Because if someone know OpAmp then he will understand the circuit easily.
If someone don't know OpAmp you may not be able to make him understand on this forum.

I dont really understand op-amps. But i understand what is happening there

Haha so I missunderstood.

Hehe, yeah.
I don't think anyone _really_ understands them.
You sit down, spend hours working out the gain stages, wire it up and never ever get the calculated results, so then you wing it, swapping out Resistor values until it does what you want.
I don't even bother with the calc stage now, just wing it on proto board right from the start.

What are calcs?

Wing it is how i roll

Dui
I think calc is necessary.
I use Opamp do many functions(comparator, intregrator, schimit trigger, etc.) in my graduate thesis, motor control.
Design in paper before trial and error can save development time.

but math is boring !

No it's not.... you can get pages of posts even out of a simple equation....

So are you just using one amp stage ?

I didn't think you like analogue

I don't, but this circuit is great, it's like digital analogue