Voltage scaling with OP AMP

FlyingFishFinger

Hi-
I've been trying to get this to work. I've got a 0-5V signal (analog) and would like to scale it to -10 - +10V. I hooked up an op amp with the chip supply at +10 and -10, the negative amp input to ground and the positive one being my signal. If I understand correctly, this should work (it doesn't).
Once I get that working, can I use the same logic to boost a waveform from my laptop soundcard to 0-5V range?
Thanks

Rafael

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~

Peter Jakacki

There are a few problems here:
1) You are not setting the gain of the opamp so it will simply use it's very high gain to swing a small signal as far as it can go. Switching in other words.

2) The opamps negative input needs to be higher than the low signal you are inputting but your input signal only goes down close to ground.

Solution:
1) Use feedback resistors to set the gain (opamp 101 basics)
2) bias the negative input up to bias the output

Set the gain for 4 altogether that is including the non-inverting gain of 1. Instead of taking the feedback shunt to ground you need to take it to 3.3V (magic number) which will correctly bias the output for +/-10V. Bear in mind that unless the opamp is a rail-to-rail opamp it's outputs won't swing to the supply rail so you may need to up your opamp supply or choose another opamp.

*Peter*

FlyingFishFinger

Yeah I just realized the feedback resistor thing >< I shouldn't have forgotten. Embaressing...
Thanks

Rafael

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
You've got to play the game.
You can't win.
You can't break even, except on a very cold day.
It doesn't get that cold.
~Laws of Thermodynamics~