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Basic Electronics » Converting input signal for ADC, impedance matching?

July 18, 2011
by kayrock
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I am trying to sample a guitar pickup. I believe that the signal coming out is +/-200mv. Could anyone point me toward a good circuit to convert this to a 0-5V signal? On a related theme, given a 0-5V output signal, and only a +5v power supply, is it possible to convert that to a +/-1v line level signal?

July 18, 2011
by Ralphxyz
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Sorry kayrock, I do not have an answer for you but there are some interesting guitar discussions in the nerdkits forums. You might ask on one of those threads to connect with someone with some answers and experiences.

Ralph

July 18, 2011
by kayrock
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Thanks ralph, I will do some searching there.

July 18, 2011
by 6ofhalfdozen
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Heya Kayrock,

Any thoughts on using a seperate ADC chip for this? It might be a lot easier than trying to build a +/-1V to 0-5V converter. There are a bunch of them out there that will do +/-1V easily with from 8 to 24bit resolution and then send it to the mcu in whatever format you prefet (SPI,UART,I2C, etc). I am not sure what sampling rate you would need, but some of the newer cheaper chips are >250KSps.(which is definately faster than standard CD sampling at 44.4KHz) In all my work with ADC's I am looking for ultralow voltage (0-300mV in 24bit res), so I haven't spent much time looking for +/- voltage ADC's but there are lots out there. For what you need, you might even be able to use some of the cheaper audio ADC's meant for audio systems. Analog devices and Texas Instruments have pretty good ADC chip selectors on their websites. just a thought.

July 18, 2011
by kayrock
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That sounds like a good idea. I already have a 12 bit external DAC in my project that I talk to via SPI at 48khz.

July 19, 2011
by kayrock
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So I played around with this some more, and the atmega has a perfectly good ADC, I dont see a need for an external ADC, and I think I will have the same issues anyway. I can currently sample and output a signal from an ipod headphone output, as well as a 0-5v signal from an avr synth that I made. The sound quality is pretty good. I guess I just need to research impedance matching buffers and dc offset for the input signal.

July 20, 2011
by BobaMosfet
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kayrock,

What you are (by definition) wanting to do is amplify the output--- doesn't that sound like you might want to look at using a transistor (a BJT) or even an op-amp, like a 741 to raise the signal from 200mV to more?

Just thought I'd give you a nudge in the right direction :P

BM

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