scaling voltages for A/D reading

ktekx

I would like to scale down a higher voltage (example: 0v-15v) to a 0v-5v level for reading. What is the best way of doing this?

Newzed

Are you talking about ADC input voltages?

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Sid Weaver
Do you have a Stamp Tester yet?
http://hometown.aol.com/newzed/index.html

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ktekx

yea, i'm measureing a varying voltage line that is around 0v-15v DC, the chip reading can only measure 0v-5v. I need to scale it down so that it can be read. Somebody mentioned OP AMPs, but I'm not entirely familiar with them.

Newzed

Use a 5K pot across your input voltage and ground.· Connect the wiper to the ADC input.· Set your input voltage for 15 volts - or the max - and adjust the pot until you get 254-255 for an 8-bit, 1023-1024 for a 10-bit or 4094-4095 for a 12-bit.

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Sid Weaver
Do you have a Stamp Tester yet?
http://hometown.aol.com/newzed/index.html

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ktekx

Cool, thanks for the fast response, I'll give it a try.

PJAllen

Op-amps not necessary -- just make a voltage divider using some high-value resistors (preferably metal-film), say three 330K in series.

Chris Savage

This was recently covered in another thread.

http://forums.parallax.com/showthread.php?p=580965

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Chris Savage
Parallax Tech Support
csavage@parallax.com

Javalin

Interestingly the formula to work out the voltage outputted to the ADC is easy :-



(quoted from: http://www.doctronics.co.uk/voltage.htm)

James