Powering op-amp with 9v battery

[nheugel]

I need to power an op amp and my only power supply availible is a 9-v battery, the goal is for the device to be portable. I need to feed into the + and - sides of the op-amp. Would I connect the positive terminal to one end and the negative terminal to the other or is there some other set up I should be using to input the + and - voltages?

 

[mingy]

It sounds like you have very little experience with op-amps, so its not that easy to answer your question. What type of op-amp are you using? I would suggest an LM358 (dual) or LM324 (quad) single supply op-amp as a readily available inexpensive choice.

Lets say you are using an LM358. (see http://www.national.com/mpf/LM/LM358.html#Diagrams ) In such a case, you connect the V+ to +9V and GND to the '-' terminal of the battery. The tricky part comes when you try and copy sample circuits, like an inverting ampflifier. You need to make a reference voltage, basically 4.5 volts, which becomes the equivalent to a 0 volt reference in a dual supply circuit. Usually you woul dtake a couple of 1K resistors in series between 9 volts and ground (GND or battery '-'). The point where the two resistors connect to each other will be 4.5 volts. You might add a 0.1 microfared capacitor between the 4.5 volts and ground points. This will work ok if all the other resistors are high values like 330K.

Anyhow, best thing is to snoop around the National Semiconductor (or TI or whoever) website and look at LM358 or LM324 Applications Notes (see http://www.national.com/mpf/LM/LM358.html#Documents or http://www.national.com/ds/LM/LM124.pdf )

Make sure you buy spare op amps and other parts because you'll probably fry a couple.
Good luck & have fun.