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DIY Stompboxes => Digital & DSP => Topic started by: ExpAnonColin on July 21, 2006, 03:34:06 PM

Title: Help me find the right DAC/ADC
Post by: ExpAnonColin on July 21, 2006, 03:34:06 PM
There are so many :(

I would like a DAC and an ADC that are
8 bit
Parallel in/out
External clock capabilities
Readily available and very common
Cheap
DIP
Preferably single supply

Help!

-Colin
Title: Re: Help me find the right DAC/ADC
Post by: Peter Snowberg on July 21, 2006, 03:51:54 PM
Good to see you around, Colin. 8)

I think the king of the 8 bit parallel ADCs was probably the National ADC080x line.
http://www.national.com/pf/AD/ADC0804.html

For a matching DAC, try the DAC08 which is currently made by Analog Devices but has been 2nd sourced from a number of other companies including Motorola.

These two chips together ruled the roost for a number of years while 8 bits was the standard.

Both devices conform to everything on your spec list.
Title: Re: Help me find the right DAC/ADC
Post by: Dave_B on July 21, 2006, 03:53:45 PM
I've used the ADC0804 (http://www.national.com/ds/AD/ADC0801.pdf) to connect a piezo drum pad to my C64.  It was real easy to use, IIRC, and you don't have to have a computer to use it.  I also had the C64 hooked to my Moog 20 years ago using a Paia 8-bit DAC card.  I can't remember the DAC they used, but I'm pretty sure it was a National part.  Maybe a DAC808? 

Digikey still has both of those (!)
Title: Re: Help me find the right DAC/ADC
Post by: Dave_B on July 21, 2006, 03:55:20 PM
Sorry, guys.  I could see that someone replied but I couldn't see what Peter wrote to know I was duplicating info. 
Title: Re: Help me find the right DAC/ADC
Post by: ExpAnonColin on July 21, 2006, 04:02:32 PM
Hey Paul,  thought I'd see an answer from you!

The ADC looks great-but the DAC (looking at DAC0800) looks like it needs a bipolar supply-anything I can use a 9v battery to power?

-Colin
Title: Re: Help me find the right DAC/ADC
Post by: Dave_B on July 21, 2006, 04:16:07 PM
Could you use a resistor ladder?
Title: Re: Help me find the right DAC/ADC
Post by: ExpAnonColin on July 21, 2006, 04:25:29 PM
Could you use a resistor ladder?

Yes, I suppose-I always worry about accuracy though.  Perhaps in the end it would be smarter/cheaper.  Can you get precision 2R resistors from Mouser?  Or anywhere else...

-Colin
Title: Re: Help me find the right DAC/ADC
Post by: Dave_B on July 21, 2006, 04:40:26 PM
Yes, I suppose-I always worry about accuracy though.  Perhaps in the end it would be smarter/cheaper.  Can you get precision 2R resistors from Mouser?  Or anywhere else...
I've only used the DAC I mentioned, but I guess the need for accuracy depends on what you're doing.  I'd be tempted to try 1% metal films. 

Have you seen this (http://www.diystompboxes.com/smfforum/index.php?topic=41151.0) thread?
Title: Re: Help me find the right DAC/ADC
Post by: ExpAnonColin on July 21, 2006, 04:43:27 PM
Yes, I suppose-I always worry about accuracy though.  Perhaps in the end it would be smarter/cheaper.  Can you get precision 2R resistors from Mouser?  Or anywhere else...
I've only used the DAC I mentioned, but I guess the need for accuracy depends on what you're doing.  I'd be tempted to try 1% metal films. 

Have you seen this (http://www.diystompboxes.com/smfforum/index.php?topic=41151.0) thread?

No, I hadn't, interesting though.  In my circuit design class last semester, we had a lab on resistor-based DAC's... R/2R and the other method I can't remember now.  R/2R was much cooler.  I think I will end up doing that.

I promise to post a schem when I'm done!

-Colin
Title: Re: Help me find the right DAC/ADC
Post by: Peter Snowberg on July 21, 2006, 06:42:38 PM
Single supply operation of the DAC08:
http://www.analog.com/UploadedFiles/Application_Notes/72999933AB6.pdf

An R-2R ladder made from 1%, 1K film SIP resistor networks can be really good. The important part is consistancy rather than absoute value. I would advise driving the ladder from a CMOS bus buffer like the 74HC573 or, if you need latching, the 74HC574. There are plenty of other CMOS buffers, but the pin layout of the '573 & '574 make them easier to deal with. If you drive them from a TTL part like the 74LS373 you'll have a greatly reduced dynamic range so more noise.

These arrays have 4 resistors in a single package with very very very good consistancy, but at a price premium considering that you need six packages.
http://www.vishay.com/docs/31510/msp.pdf

Once you get an ADC0804, try an R-2R ladder with regular old 5% 1K resistors which are all from the same package, hook up a triangle wave generator to the ADC input, and watch the output on a scope. The results may be more than close enough for rock&roll.

The other Q&D methos is called weighted summing and for that you probably want to use 0.1% resistors, but you only need 8 of them as long as you can get the right values.
Title: Re: Help me find the right DAC/ADC
Post by: ExpAnonColin on July 22, 2006, 04:54:59 PM
The single supply operation looks a little overcomplicated...  I think I will end up with R/2R if it is easy enough to get good results.  It was OK in my circuit design class, but we used no buffers.

-Colin
Title: Re: Help me find the right DAC/ADC
Post by: ExpAnonColin on July 22, 2006, 05:25:29 PM
I was hoping to get a sample of the 0804 but can't really source one... any ideas where I could get 3 or so without having to pay priority shipping?

And maybe some 4049's too?  :)

-Colin
Title: Re: Help me find the right DAC/ADC
Post by: R.G. on July 22, 2006, 05:39:48 PM
At the risk of restating the obvious, both PIC and AVR uC's have built in ADC capability to about 10 bits, and PWM capability to about the same resolution.

The primary limit you'll find with these is that they're not going to ... quite... make full audio within the single chip.

They're $2.00 to $5.00, available lots of places, and generally have more than one channel of each.

And the rest is A Simple Matter Of Programming.    :icon_biggrin:
Title: Re: Help me find the right DAC/ADC
Post by: ExpAnonColin on July 22, 2006, 05:41:06 PM
At the risk of restating the obvious, both PIC and AVR uC's have built in ADC capability to about 10 bits, and PWM capability to about the same resolution.

The primary limit you'll find with these is that they're not going to ... quite... make full audio within the single chip.

They're $2.00 to $5.00, available lots of places, and generally have more than one channel of each.

And the rest is A Simple Matter Of Programming.    :icon_biggrin:

I'm just making a bit crusher.  No programming here.

-Colin
Title: Re: Help me find the right DAC/ADC
Post by: Arno van der Heijden on July 24, 2006, 11:02:10 AM
Please post a schematic when you're done!!  :icon_mrgreen: :icon_razz:
Title: Re: Help me find the right DAC/ADC
Post by: Celadine on August 24, 2006, 12:32:40 AM
FYI - The AVRs' on-board ADCs have a top (incoming signal) frequency limit of something like 3.5 kHz.  They buried that one in the manuals, its not specifically stated.   :icon_confused: