IC Op-Amp Cookbook Walter G. Jung
Publisher: Prentice Hall

Or check out "ic op-amp cookbook" by Walter G. Op amps, a type of IC chip that is very cheap and easy to work with, are used exactly for that purpose. Use a search engine to look up 'OP AMP COOKBOOK'. A circuit simulation to get a better understanding of how it works, maybe sweep the value of R354. Http://www.amazon.com/Op-Amp-Cookbook-3rd-Walter-Jung/dp/0138896011. Check out the datasheet of the lm386 for some simple ideas. This book covers basic OP-AMP theory in excellent detail. TONS OF IDEAS AND APPLICATIONS!!! I assume I would have to tweak some resistor values in order to make the circuit run at this lower supply . An appendix containing manufacturers' data sheets. Also try the "Op Amp Cookbook," "IC Timer Cookbook" and others by Walter Jung. Apparently it's an offset nulling resistor array, described in The IC Op-amp Cookbook. The original circuit runs on 12 VDC, but since the A/D converter IC must be supplied with 5 VDC only I want to scale down the circuit, so that 5 V is the maximum voltage present. This edition includes: Over 200 practical circuit applications. It is available in IC (Integrated Circuit) chip. The supply voltage is connected to the op amp to measure its level.