Oh That Stuff: Operational Amplifiers

Operational AmplifierThese past two weeks at work have been a re-introduction to ECE 320: Electronic Devices and Controls. I have to do something that is very simple conceptually, but continually reminds me why I am not a hardware guy with how complex it actually is.

The problem:
I’ve got a signal that runs from 0 to 18 Volts. I have an analog to digital converter board that can handle voltages from -10 to 10 volts. I need to essentially subtract 10 volts from my input signal. In C:

signal = signal – 10;


In hardware this involves 4 resistors and operational amplifier and expensive 10 volt reference, two regulators and power supplies to handle the power requirements, and more capacitors than you can shake a stick at. Save me now.

Well, I got some help, cause we employ people who actually know how to do this stuff and he came up with some designs for me. But I had to check them out. He told me what they would do, but I had to confirm, build it, and test it. I was very impressed with myself in how much I remembered. I was able to, in the span of half an hour, figure out the whole thing, including all the intermediate steps. It was just like taking a test in college. I can now add another class to the list of classes where I learned something that I have applied directly in work. There are a lot of those by the way. Maybe OSU CSE isn’t as bad as I thought it was in school.

The circuit didn’t work when I tested it. Today we discovered I managed to screw up and pick the one, in stock, op amp available that is not at all what I need. It was a current feedback amplifier, whatever that is. Apparently there are more than one kind; but can’t blame the ECE department for not telling me that. I’m not supposed to have to worry about this stuff.

One Response to “Oh That Stuff: Operational Amplifiers”

  1. Rob says:

    signal -= 10;