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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
question about voltage adder for 8 bit audio
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EATyourGuitar



Joined: Oct 28, 2010
Posts: 59
Location: Providence, RI

PostPosted: Wed Sep 28, 2011 8:02 pm    Post subject: question about voltage adder for 8 bit audio Reply with quote  Mark this post and the followings unread

I want to take a parallel 8 bit signal and convert it to an analog 8 bit word for audio. I'm guessing a small signal diode and a 100k resistor on each pin should do it. I'm using various CD4000 IC's. I realize that the answer is probably to use a DAC but I have never used one and I'm not sure how they function at extremely low clock rates. I also want to consider using N number of bits in parallel, not just multiples of 8. thats why I'm after the passive approach. I would be ok with using more IC's though. anyone have any experience on this?

also, another noob question. if I want to make modules for my MOTM system (+15, 0 , -15) should I just throw a 9v regulator on +15 for all my logic circuits? how does the V+ voltage affect threshold and voltage of logic going high?
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Kabzoer



Joined: Feb 07, 2011
Posts: 82
Location: Belgium

PostPosted: Thu Sep 29, 2011 11:30 am    Post subject: Reply with quote  Mark this post and the followings unread

The easiest way I can think of is using an R2R-ladder, see the Wikipedia article:
http://en.wikipedia.org/wiki/Resistor_ladder#R-2R_resistor_ladder_network_.28digital_to_analog_conversion.2C_or_DAC.29
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DGTom



Joined: Dec 08, 2008
Posts: 211
Location: Adelaide
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PostPosted: Thu Sep 29, 2011 4:30 pm    Post subject: Re: question about voltage adder for 8 bit audio Reply with quote  Mark this post and the followings unread

EATyourGuitar wrote:
I realize that the answer is probably to use a DAC but I have never used one and I'm not sure how they function at extremely low clock rates.


a DAC will work just fine right down to 0Hz & with quite large numbers, you could easily use 16-24 inputs for an R/2R. I'm using 4bit DACs for a wierd CMOS S&H at the moment. A voltage gets stored to a shift register for infinite hold times; if the inputs of an R/2R are not changing the output is just a steady voltage.

of course, with 8 bits you could put them thru pots Wink


I would just use +15V & put either transistor or op-amps between the outside world & the CMOS, you could use 10V to make scaling the output easier tho
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EATyourGuitar



Joined: Oct 28, 2010
Posts: 59
Location: Providence, RI

PostPosted: Fri Sep 30, 2011 10:21 am    Post subject: Reply with quote  Mark this post and the followings unread

good information guys. in my daydreams I figured that the resistor ladder was one option. I see that in the wiki they use it like a DAC where each bit has a magnitude of 2. they also have an example using equal resistors. I'm more interested with unity mixing where each bit is added equally. I realize that my real world bit resultion is actually more like decimal 8 which is actually only 2^3 or 3 bit DAC. yes 3 bits is way dirty but It lets me make CV signals that follow the distribution of 1's and 0's sitting in a shift register. I will probably run it through a slew or filter anyway.

oh and what about a dac with parallel input. does that exist?
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