Cheap 12 bit DAC and ADC's

[Martin Riddle]

I'm looking for a cheap 5v Rail buffered output 12bit DAC
And a 12bit ADC (8 channel).

Any recommendations?

Cheers

 

[John Larkin]

I'm looking for a cheap 5v Rail buffered output 12bit DAC
And a 12bit ADC (8 channel).

Any recommendations?

Cheers

For the ADC, maybe an ADS7866 and an HC4051?

John

 

[Joerg]

I'm looking for a cheap 5v Rail buffered output 12bit DAC
And a 12bit ADC (8 channel).

Any recommendations?

Define "cheap". Also, none of them truly goes to the rail if that's what
you want. Many are 0V to 4.095V because that gives you a nice 1mV
granularity. Others go by whatever external ref you provide.

 

[Frank Buss]

I'm looking for a cheap 5v Rail buffered output 12bit DAC
And a 12bit ADC (8 channel).

Any recommendations?

Depends on your requirements. There are huge price differences depending on
speed. And there are different interfaces, like SPI or parallel and you
might not like BGA style parts.

A good source for selecting the right part is the parametric search at
Digikey, even if you don't buy it there:

ADC:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556291

DAC:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556292

Not cheap, but nice and fast is the LTC2624, which is on the Spartan3E
evaluation kit, with which I've implemented my signal generator:

http://www.frank-buss.de/SignalGenerator/

 

[Joerg]

Depends on your requirements. There are huge price differences depending on
speed. And there are different interfaces, like SPI or parallel and you
might not like BGA style parts.

A good source for selecting the right part is the parametric search at
Digikey, even if you don't buy it there:

ADC:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556291

DAC:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556292

Not cheap, but nice and fast is the LTC2624, which is on the Spartan3E
evaluation kit, with which I've implemented my signal generator:

http://www.frank-buss.de/SignalGenerator/

I like the AD5328 and the AD7928 but they aren't exactly cheap.

 

[Martin Riddle]

For the ADC, maybe an ADS7866 and an HC4051?

John

I should have mentioned SPI, But I think the AD7927 is the one, half
the cost of the LT part we are using now.
The are some Dacs that are priced right from analog too.

If I had extra port pins then the Mux I would play around with, but
thats not an option.

Thanks

 

[Joerg]

I should have mentioned SPI, But I think the AD7927 is the one, half
the cost of the LT part we are using now.

That falls under "cheap"? Hmm, you guys leave too much money on the
table

The are some Dacs that are priced right from analog too.

If I had extra port pins then the Mux I would play around with, but
thats not an option.

At that cost I'd consider muxing the SPI stream so you can hang a
register onto the SPI that rotates through the ADC channels. Not an
option for the DACs though.

 

[Frank Buss]

I like the AD5328 and the AD7928 but they aren't exactly cheap.

There are some cheap high quality audio DACs, but I don't know if they can
go down to DC.

 

[Joerg]

There are some cheap high quality audio DACs, but I don't know if they can
go down to DC.

They used to, but at least the ADC part of audio codecs often has
inherent highpass filtering in there which can't be turned off. Learned
it the hard way when I wanted to hack a laptop into going down to below
1Hz. But it did go down to about 5Hz.

Also you usually get only two channels. Example of a really cheap audio
DAC, for 3.3V supply though:
http://www.nxp.com/acrobat_download/datasheets/UDA1334TS_2.pdf

They don't even spec the offset of the opamp that does the current to
voltage conversion. It could very well be above the 12bit granularity
because it doesn't matter to the audio guys.

 

[Frank Buss]

They don't even spec the offset of the opamp that does the current to
voltage conversion. It could very well be above the 12bit granularity
because it doesn't matter to the audio guys.

Sometimes it matters. If you have a sample rate change and you have to
disable the output before changing the clock for the DAC to avoid any
clicking noise, it could be a problem. I know a schematic with lots of
transistors, op-amps and a relay, for which I've designed and implemented a
software concept (including FPGA functions), which is really necessary to
avoid any clicking noise for professional audio monitoring systems, where
you can get deaf at signal levels of 0 dBu. I don't care, but looks like
radio broadcasting customers do

 

[Joerg]

Sometimes it matters. If you have a sample rate change and you have to
disable the output before changing the clock for the DAC to avoid any
clicking noise, it could be a problem. I know a schematic with lots of
transistors, op-amps and a relay, for which I've designed and implemented a
software concept (including FPGA functions), which is really necessary to
avoid any clicking noise for professional audio monitoring systems, where
you can get deaf at signal levels of 0 dBu. I don't care, but looks like
radio broadcasting customers do

True, don't ever touch the clock rate or data stream, then it is indeed
a problem. Curing that at the output is like a squelch and it seems that
even manufacturers of professional communications gear no longer fully
understand how to handle this. As evidenced by the popping squelch and
the schematic a guy at the German NG posted a while ago (Michael, the
one with the large model railroad). That was a truly horrid circuitry.

BTW, after we had our "glorious" switch to DTV (don't even get me
started on this #@^&!! ...) we now "enjoy" the occasional tsk, pop, pock
and phsst sound when video content such as news reporter pieces changes.
Oh, and the movie we wanted to watch yesterday pixelated out into a blue
screen, as usual.

 

[Martin Riddle]

That falls under "cheap"? Hmm, you guys leave too much money on the
table



At that cost I'd consider muxing the SPI stream so you can hang a
register onto the SPI that rotates through the ADC channels. Not an
option for the DACs though.

Well I could add like a 74HC595 and feed the mux with that. I think I
have 1 or 2 pare port pins.

Also For the DAC I found a microchip part MCP4922, $3.

Cheers

 

[E]

Also For the DAC I found a microchip part MCP4922, $3.

Microchip? hmm..
For the ADC maybe a dsPic with simple program to output data via SPI, $3
Some devices have inbuild 16-bit DAC also (like dsPIC33FJ64GP802)

 

[Joerg]

Well I could add like a 74HC595 and feed the mux with that. I think I
have 1 or 2 pare port pins.

Well, there's the solution. All you need is to disassert the device
select for the DACs/ADCs and run another CS line to the 595, then use
the regular (same) SPI lines for clock and data.

Also For the DAC I found a microchip part MCP4922, $3.

But that's only a dual DAC. Plenty of those.

 

[Joerg]

Do you have a few favorites?

Not really, each circuit situation is just too different and sometimes
tricks need to be played with the DACs. I like the AD5328 and the AD7928
for ADC when I have to have lots of channels (if I need more than one
channel it's usually lots of them). For a 2ch DAC the DAC7612 is kind of
ok at $3, although a long hard search should turn up less expensive
ones. Whenever I have a project I go by price and most of all widespread
availability. Certain parts are on the black list, but we all know who's
those are.

Most of the time my clients already have DACs or ADCs in their designs
and prefer that I use the same.