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Old 28th March 2006, 02:51 AM   #11
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the least expensive, standalone isolated data-acquisition USB device I have seen is $549...but I haven't done that much looking as an analog opto isolator chip from Vishay or Avago is only a couple bucks -- about the cost of a decent opamp.
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Old 28th March 2006, 11:59 AM   #12
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by andrei

I'd rather isolate the digital bus... Does anyone know if there is off-the-shelf galvanic isolator for USB?
Actuallly, I am not sure youc an isolate the USB bus, but f you chose a USB codec interface with an external codec, you could isolate the codec-interface link. Look at the ADUM series of galvanic isolators from Analog Devices - fairly cheap, very fast, great isolation.
BTW be careful with PC codecs, most have a built in digital high pass for both input and output, so you can't get DC in or out
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Old 28th March 2006, 12:34 PM   #13
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you can also isolate with a voltage-to-frequency converter --- if you square up the pulse on the other side you can directly read the value off the parallel port.

the article by Steber can be found here:
"Tracing Current and Voltage: Design a Unique PC Sound Card Curve Tracer", by George Steber, p. 56 Jan 2004
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Old 29th March 2006, 11:15 PM   #14
andrei is offline andrei  Canada
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Quote:
Originally posted by ilimzn
BTW be careful with PC codecs, most have a built in digital high pass for both input and output, so you can't get DC in or out
You are right. I really did not want to screw around programming MCUs, but I guess I'll have to. I've ordered a few of Silicon Labs evaluation boards. (BTW, one of them is 1Msps dual 16-bit SAR ADC with USB interface. At $25, that is by far the cheapest data acqusition board I've seen. If it performs anywhere near the specs, it will make an awesome PC scope...)

On the analog side, things are shaping up. Heater and screeen supplies will be regulated switchers running from 15V/35W floating DC. I am inclined towards manual controls for them, but I guess adding provisions for DAC control could be made...
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Old 30th March 2006, 02:55 AM   #15
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fwiw -- this is a two channel, "positive going" ADC isolator with a 10Hz LPF -- should be able to derive a real 12 bits of info without risk to your PC -- the "cheat" is that it borrows 5 VDC from the USB bus to power the isolated side's opamps (which are rail to rail devices that I had on hand). I worked this out for SMT, the prior version used through-hole devices:

Click the image to open in full size.
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Old 18th August 2007, 08:15 AM   #16
Yvesm is online now Yvesm  France
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Hi there !

I'm working a bit slow, but I really work !
Here is a screen capture of the current display:


Click the image to open in full size.

Data where sampled using a very simple (and for from perfect) setup like this one:

Click the image to open in full size.

The outputs labelled "To O'scope" was used to feed a "standard" PC sound board inputs.

I'm while trying to obtain stairsteps from the sound board output too.
A kind of AC/DC up converter :

Click the image to open in full size.

Any simple suggestions appreciated !
To be continued . . . .

Yves.
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Old 18th August 2007, 11:06 AM   #17
EC8010 is offline EC8010  United Kingdom
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Three cheers for Yves! An excellent set of results.
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Old 18th August 2007, 12:49 PM   #18
SY is offline SY  United States
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Yves, pardon a dumb question, but... is there an easy way to generate a sine or sawtooth wave that can be varied in amplitude, but always has its most negative-going part at zero or some small fixed voltage?
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