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Old 13th August 2003, 01:24 AM   #1
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Default Digital Pot for GC

Well, I built a digital pot for my GC as an experiment, and it turned out pretty well. I used a Dallas DS1802 http://pdfserv.maxim-ic.com/arpdf/DS1802.pdf in Stereo mode. Attached is the view of a 1 kHz 1Vpp sine wave at the inputs and outputs of one channel. Ch1 is the output of the pot, Ch2 is the input. I done have a waveform analyzer to measure distortion, just a 500MHz 2Gs/Second scope. It works pretty well so far, and I am using it between my XM Satellite radio and amp.

Nik
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Old 13th August 2003, 02:32 AM   #2
Elkaid is offline Elkaid  Canada
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If you're looking for an even more high end digital pot, look for BB's PGA2310.
http://focus.ti.com/lit/ds/symlink/pga2310.pdf
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Old 13th August 2003, 02:44 AM   #3
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Quote:
Originally posted by Elkaid
If you're looking for an even more high end digital pot, look for BB's PGA2310.
http://focus.ti.com/lit/ds/symlink/pga2310.pdf
Yup. Nice chip.

One nice thing about the Dallas chip is that it doesn't require any sort of digital interface to control it. You can use simple pushbuttons which is a big plus for those who don't want to mess with microcontrollers.

se
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Old 13th August 2003, 03:08 AM   #4
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Yes, the Dallas pot is nice for the pushbutton control. It also is powered from +5V. There is a slight performance tradeoff, but it's minimal.
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Old 13th August 2003, 03:57 AM   #5
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I have some 1806`s sitting here and havent had the time to test them...glad to hear someone has had success in utilising them

DIRT®
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Old 13th August 2003, 03:58 AM   #6
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Mantram-

Cool. I use an XM SkyFi as my favorite source. I love it. Have a thread with my new headphone amp and skyfi just up tonight:

My new baby

How hard was it to incorporate the Digital pot? Did you run another PSU for the 5v?

Could you post a circuit, with PSU included??

Thanks,

GnD
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Old 13th August 2003, 04:14 AM   #7
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Did you have to build Wheatstone bridges for each of the channels? And does it knock out the DC offset as it goes thru the chip, or do you have to remove it?

GnD
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Old 13th August 2003, 04:18 AM   #8
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Quote:
Originally posted by GrahamnDodder
Mantram-

Cool. I use an XM SkyFi as my favorite source. I love it. Have a thread with my new headphone amp and skyfi just up tonight:

My new baby

How hard was it to incorporate the Digital pot? Did you run another PSU for the 5v?

Could you post a circuit, with PSU included??

Thanks,

GnD
I'm testing the digital pot for inclusion into what I'm calling a "SatAmp", a GC specifically for Satellite radio. It includes a digital pot on the input, and a pair of 3" full range drivers. It will also incorporate either a SkyFi car cradle, or the new Roady Delphi Rx that incorporates the antenna and audio connectors. I'll post a schematic tomorrow, because I left it at work. It is currently powered by an LM7805 off of a 12VDC wall wart, but the circuit will ultimately be powered off of the GC's PSU for simplicity. I'm probably going to be sampling some other digital pots, including the DS1666, which is a single linear taper pot with eeprom to store the wiper settings on power off. I'll use two to eliminate any possible crosstalk. I initially had some hum which was solved by better star-type grounding on the board.

More tomorrow.

P.S. moderators, would it be possible to get off of moderation and be allowed to include images and edit posts?
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Old 13th August 2003, 04:21 AM   #9
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BTW here is my current setup, in the absence of my GC, which parts are being gathered for now:

http://www.xmfan.com/viewtopic.php?t=9163
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Old 13th August 2003, 04:28 AM   #10
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Quote:
Originally posted by GrahamnDodder
Did you have to build Wheatstone bridges for each of the channels? And does it knock out the DC offset as it goes thru the chip, or do you have to remove it?

GnD

I didn't use the Wheatsone bridges, and If I had permission to post images, I'd post a screen capture from my scope that shows a 1 kHz square wave at 1vpp on the input and output of the pot. There is about 2-3 mv DC offset on the low side of the square wave, but I haven't done anything about it. I may try some caps on the input to the pot, similar to what is used on the GC's input. The Whaetsone bridges add too much complexity vs. benefits. I like things "simple without sacrificing features".

Schematics tomorrow.

Nik
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