# Analog to digital conversion for a project

digitalblggr
Hey guys,

I am trying to do analog to digital conversion for a project. I don't want to use the digital chip, but want to do it in analog. I need 8-bit resolution. I found one approach: string resistor ladder. It uses 2^n-1 resistors. For 8-bit conversion I will have to use 255 resistors which is way too much since my final project will be housed on a small PCB. Any suggestions for a better approach?

Thanks

Mentor

Hey guys,

I am trying to do analog to digital conversion for a project. I don't want to use the digital chip, but want to do it in analog. I need 8-bit resolution. I found one approach: string resistor ladder. It uses 2^n-1 resistors. For 8-bit conversion I will have to use 255 resistors which is way too much since my final project will be housed on a small PCB. Any suggestions for a better approach?

Thanks

Yes. Use successive approximation, a DAC, and a comparator instead.

Fish4Fun

digitalblggr,

I don't know what your "project" is, but unless it IS building an ADC from components, using an ADC IC sure is a better way to go. If you plan on having an on-board uController, you could even select one that has a built-in ADC (the AVR family is a good example.) For <$10 you can get an ADC, a DAC, and a very powerful uController with a lot of other capabilities......but it depends on what your project actually is. I have used both the DACs and ADCs in the ATMegas, you can do amazing things with them. Good Luck! Fish digitalblggr Yes. Use successive approximation, a DAC, and a comparator instead. This sounds interesting. So I am trying to use as few digital components as possible just as a challenge. Do you think it would work if I used R2R ladder http://en.wikipedia.org/wiki/File:R2r-ladder.png instead of DAC ( the problem I run in there is that apparently: "On a printed circuit board, using discrete components, high precision resistors of 1% accuracy may be employed for a 5 bit circuit, however with bit counts beyond this the cost of ever increasing precision resistors becomes prohibitive." I don't know what your "project" is, but unless it IS building an ADC from components, using an ADC IC sure is a better way to go. If you plan on having an on-board uController, you could even select one that has a built-in ADC (the AVR family is a good example.) For <$10 you can get an ADC, a DAC, and a very powerful uController with a lot of other capabilities......but it depends on what your project actually is. I have used both the DACs and ADCs in the ATMegas, you can do amazing things with them.

So I am building a digital voice recorder, which will sample human voice at 8 Khz and then convert it into digital signal at 8-bit resolution. I am in fact using the Avr mega32 which has in-built ADC, and that's my fall back plan. I just wanted to attempt building ADC and DAC from the scratch because it sounds interesting, and I want to play around with analog circuitry.( Sadly the rest of my project has very few analog components; it's just a bunch of filters and amplifiers)

Fish4Fun

The ATMega32 is an awesome member of the AVR family. Maybe you should consider going the other way...instead of seeing how many analog circuits you can build from scratch and cram onto your PCB, perhaps you should see how few components you can use to complete the project? Just a thought. Obviously the digital voice recorder is a "challenge" project (or you would simply buy something from this page: http://onlinecatalog.digikey.com/WebProject.asp?CodeId=7.4.4.16&pagelabel=682# )

Anyway, have FUN with your project!

Fish

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