Sigma Delta ADC resistor question

W9GFO

I am making a Sigma Delta circuit to measure battery pack voltage. The Battery packs could be up to about 7 volts so I will use a voltage divider consisting of 180 k and 150 k resistors.

The Sigma Delta circuit described in the Counters App Note calls for a 150 k resistor in series with the VIN. I'm assuming that I still need that resistor even though there is already a 180 k resistor in series with the battery. To be sure though I thought I would ask.

Do I need that 150 k resistor between the voltage divider and APIN?

Rich H

Phil Pilgrim (PhiPi)

I would skip the divider entirely and use a 330K series resistor between Vin and the APIN, along with the 100K feedback resistor. This will give you at least the 0-7V dynamic range you're after. Just be sure to calibrate it at two points: 0V and 7V.

-Phil

W9GFO

Thanks Phil, I had a feeling there was a way to use fewer resistors but wasn't seeing it.

Rich H

Rayman

Here's a little app to help pick resistors:

http://www.pulsedpower.net/Applets/Electronics/SigmaDeltaADC/SigmaDelta.html

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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm

Mike Huselton

Rayman,

I especially like the Pulsed Power Home page. Lotsa unit conversions, Maxwell equations, etc. I'll add this to my collection.

There is a Firefox app that creates a compact link to Wolfram Alpha. It works like a google Search box. Enter any quantity such as 1000 hz, 47 pf, etc and a result is calculated to convert to a variety of expressions, formulas and examples. Explaining it takes far too long - just install the Firefox Add-on. This is still blowing my mind and is so intuitive to use.

Tools -> Add-ons -> Get Add-ons
See All Results -> Experimental - Wolfram|Alpha

This is transforming my web use. I hope Chip is using this.

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JMH