Voltage

Judith · 2007-07-18 13:19

Hey--
I'm trying to make some simple circuit things for a local rocket competition. Sorry if my question isn't worded clearly, this is my first time doing this sort of thing.
Anyways, I was wondering whether you guys knew whether/how I could amplify the output of a barometer so that i could get a clearer reading of the lower values? Say, increase the 2.5 V-4.3V range to 0-5V, since that's the range that my ADC can read? I've read about step up transformers, but that would just double or triple the voltage supply--2.5 would just become 5, I couldn't make it 0, right?

Thanks

Mike Green · 2007-07-18 13:37

You need an op-amp (operational amplifier) which is a general purpose fairly precise amplifier. Most op-amps have a differential voltage input where their output is proportional to the voltage difference between the two inputs. You would use a voltage divider to provide 2.5V (the lower end of your range) from your 5V supply and connect that to the (-) input of an op-amp. You'd connect the barometer to the (+) input and adjust the gain of the op-amp (using a feedback resistor) so the output goes from 0-5V with an input range of 0-1.8V.

For a discussion of op-amps and their use, try the Wikipedia (Google "Wiki operational amplifier")

Dave Hein · 2007-07-18 16:55

Judith,

I agree with Mike Green's suggestion. However, there may be other ways to do it. Which ADC are you using? It may have built-in offset and gain controls. If it is an 8-bit ADC you could get a gain of 16 by going with a 12-bit ADC.

There has been a lot of discussion about altimeters on the Rocketry Forum. I did a search for the keyword "altimeter" and the reults are at www.rocketryforum.com/search.php?searchid=19631.

Dave

Judith · 2007-07-18 18:15

Thanks a lot Mike and Dave, that's really helpful. I'm using a 12-bit ADC. I'll check out the rocketry forum, I'm sure I'm not the first person who's encountered this problem.

Voltage

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