d/a conversion

Cyberpageman

I need to produce reasonably precise voltages between 0 and, say, 5 volts to control an x-y recorder. Is it possible to use the BASIC Stamp to do this directly, or through a d/a converter chip?

Thanks

pwillard

There is no analog out, per se.· PWM is not what you·want.· Actually, there really is very limited analog I/O built in.

You have pretty much answered your own query.· You want an external·D/A solution.· Now it comes down to how accurate you need to be.

You could use and R/2R Ladder with a voltage follower at the cost of a lot of I/O pins, or you could use a simple two wire (AKA I2C)·protocol·MAXIM part called MAX518.

http://www.ortodoxism.ro/datasheets/maxim/MAX517-MAX519.pdf


Me?· I'd go for using the MAX518 or something similar.· I've also been playing with real obscure parts like the I2C TDA8444· (No results to show for it yet)



Post Edited (pwillard) : 8/2/2007 8:35:20 PM GMT

Mike Green

What do you consider reasonably precise? How fast does this voltage need to change?

You probably will need to use an external DAC. The Stamp can put out voltages from near zero volts to near Vdd (about 5V) to about 2 significant places using a resistor and capacitor.

Cyberpageman

Thank you both for your help. I'll take your advice and use a DAC--that is just the information I needed.

Cyberpageman

PJAllen

Well, Cyberpageman has probably left the building, but...

pwillard

Honestly... you might actually have some trouble finding an MC1408 nowadays since it's pretty well obsolete. You might find a NTE2056 equivalent, but... look at how many I/O pins you need. I2C starts to make more sense.

Cyberpageman

Thanks for the NTE2056 suggestion. I have a lot to learn.

PJAllen

Yep, the ol' DAC0808, scarcer'n hens' teeth... don't get much call for them round these here parts, stranger...·probably have to hunt them up at·some niche outlet...

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=14947

Bruce Bates

Gents -

The DAC0808 is not quite as scarce as hen's teeth, as the trusty FindChips search engine
[noparse][[/noparse] http://www.findchips.com/ ] indicates there are at least 10 distributors who carry them, including Jameco.

Regards,

Bruce Bates

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OzStamp

Hi

What about the R2R method with a OPAMP follower.
Has worked for me on several occasions...

cheers

Ronald Nollet Australia

Cyberpageman

There is a discussion of a R2R Ladder DAC at file:///C:/Documents%20and%20Settings/HP_Administrator/Desktop/Ultrasonics/dac.htm. Maybe this would be enough to position the pen of an x-y plotter.

I looked up the DAC0808, and it seems like an elegant solution too.

I suppose I can use the STAMP to supply the binary input. I haven't had a chance to study how.


Tony Russell

Tracy Allen

Since you have to control an x-y recorder, you probably need a dual output. Have you considered a serial DAC that use the SHIFTOUT command? Here are links to code for the TLV5618 and the MAX5722. These are 12 bit dual DACs in 8 pin packages. TI and MAXIM are both helpful with free samples.

http://forums.parallax.com/showthread.php?p=555268
http://forums.parallax.com/showthread.php?p=553090

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Tracy Allen
www.emesystems.com

pwillard

Just to clarify what I mentioned earlier.

The MAX518 is a dual DAC with rail-to-rail 5V output·that uses I2C serial communication (IE; Data Pin & a Clock pin) so only 2 I/O pins on the stamp are needed.· Jon Williams did some excellent Nuts&Volts articles on using I2C style devices so you don't even have to re-invent the wheel on this one. Easily obtainable from DIGIKEY for about $6.00 each.