Replace analog pot with digital pot?

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tomas02
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Replace analog pot with digital pot?

Post by tomas02 » Mon Feb 14, 2011 11:45 pm

I want to replace the analog potentiometer with a digital one for my xbox laptop.
The analog one has 6 pins so can i just desolder that and get a digital pot or do i need to make a little circuit?
Also analog pot is a B10K.
Thanks

17daysolderthannes
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Re: Replace analog pot with digital pot?

Post by 17daysolderthannes » Tue Feb 15, 2011 12:27 am

analog pot on what...the joysticks? I think the question is what the output is on the digital one you'd like to use. I don't know much about the way the circuit is laid out, but I'd venture to guess swapping it with a digital one or even a non-analog one would entail quite a bit of hardware and software tomfoolery.

tomas02
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Re: Replace analog pot with digital pot?

Post by tomas02 » Tue Feb 15, 2011 1:09 am

Is for speakers with amp could I wire it in to the audio cord and leave other one?

Snow_Cat
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Re: Replace analog pot with digital pot?

Post by Snow_Cat » Tue Feb 15, 2011 11:12 am

Yes, though if you do decide to replace it you will need to make a little circuit, but I can help design that.

The circuit will contain
  • Digital Potentiometer(s)
    • One potentiometer per channel
  • Jumpers
    • input/output/supply
  • buttons
    • increase/decrease/reset/mute
  • (timer)
    • pulses so that you don't need to (click,click,click,click)
Could you post a picture of the potentiometer (and the opposite side of the PCB) so that I can figure out the wiring?

tomas02
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Re: Replace analog pot with digital pot?

Post by tomas02 » Wed Feb 16, 2011 5:40 am

Thanks Snow_Cat.
Here are some links to pictures of sound amp with pot removed. there are 8 pins because the back 2 pins are the power switch which I'm going to wire a push button to.
http://tomas02.yolasite.com/resources/I ... 73x279.JPG
http://tomas02.yolasite.com/resources/I ... 56x191.JPG
http://tomas02.yolasite.com/resources/I ... 56x191.JPG

Thanks for the help

Snow_Cat
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Re: Replace analog pot with digital pot?

Post by Snow_Cat » Wed Feb 16, 2011 1:08 pm

Could you take some resistance measurements for me so that I can see the correct pot value.

Code: Select all

1──┤R1├──2──┤R2├──3
└──────┤R3├───────┘

4──┤R4├──5──┤R5├──6
└──────┤R6├───────┘

7──────┤R7├───────9
I am expecting R1=R4, R2=R5, R3=R6=R1+R2=R4+R5, R7=closed/open.

tomas02
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Re: Replace analog pot with digital pot?

Post by tomas02 » Thu Feb 17, 2011 3:51 am

will get that done when i find my multimeter in next day or so.
how far should i have knob turned when doing this? all the way? half way?

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Re: Replace analog pot with digital pot?

Post by Snow_Cat » Thu Feb 17, 2011 7:57 pm

If you turned it half-way (rotation wise) that would tell me if it is logarithmic or linear.

But it should not make that much of a difference functionally.

tomas02
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Re: Replace analog pot with digital pot?

Post by tomas02 » Tue Apr 12, 2011 2:13 am

Im really sorry its taken so long but have been busy but here are resistances

1──┤R1├──2──┤R2├──3
└──────┤R3├───────┘

4──┤R4├──5──┤R5├──6
└──────┤R6├───────┘

7──────┤R7├───────9
R1=3.92
R2=6.42
R3=9.82
R4=3.76
R5=5.73
R6=9.30
R7=0.00

These were all taken with meter set to 20k ohms

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Re: Replace analog pot with digital pot?

Post by Snow_Cat » Tue Apr 12, 2011 8:40 pm

If that is at about the halfway point mark then it is not quite log and not quite linear. I'll assume that is called 'audio' for the other options are apparently 'linear' and 'log'.

I'll assume that 7-9 is a normally closed switch.

(search results)
  • Integrated Circuits (ICs), Data Acquisition - Digital Potentiometers
    • digikey.com10K Audio
      10K is the closest 'normal' size to what you measured, and other "Audio" pots include 20K and 45K.
      • maxim-ic.comMAX5456,MAX5457
        $3.00 (CDN) and designed to use push buttons!
        While 3-wire SPI can also be operated by pushbuttion (I've done it before) strictly speaking it would not be user friendly.
Okay, drawing circuit...
Oops.
Could you set the pot to "mute" and remeasure?

tomas02
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Re: Replace analog pot with digital pot?

Post by tomas02 » Wed Apr 13, 2011 12:33 am

with pot turned all the way to left without doing click of switch so switch on but pot off (if that makes sense)
R1=0
R2=9.8
R3=0
R4=0
R5=9.3
R6=9.3
R7=0

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Re: Replace analog pot with digital pot?

Post by Snow_Cat » Wed Apr 13, 2011 2:49 pm

I am going to assume that your measurement for R3 was some sort of error.

Also, the IC is 4x4mm with a pitch of 0.65mm.

docs.google.com2011.04.12.pdf contains
  1. Schematic
    • Based on reference design.
  2. Component Layout
    • Only top traces are needed, bottom is redundant to top and components.
    • "A" shaped pinout is emulated for convenience.
    • The all important MUTE button is seperated from the other three for convenience
    • Note "■●●" is "123".
    • Can be redesigned for different button placement or headers to buttons if requested.
  3. PCB front
    • Both capacitors are 0.1µF
    • Four push buttons are B3F-10XX style
    • Switch is 'small' style
    • LED and resistor remain to be calculated/determined.
  4. PCB back
    • Contains redundant traces for convenience.

tomas02
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Re: Replace analog pot with digital pot?

Post by tomas02 » Wed Apr 27, 2011 4:05 am

Hi,
Thanks so much for that
just a question or two
What is the mode switch for?
how would the design change to have one header for all buttons?
Thanks in advance

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Re: Replace analog pot with digital pot?

Post by Snow_Cat » Wed Apr 27, 2011 2:16 pm

The 'mode' switch toggles the use of the other two buttons so that you can adjust either the channel balance or the volume.
I could redesign using the MAX5456 that has seperate buttons for volume and balance if you want (but that will require more buttons).

docs.google.com2011.04.27.pdf desribes the button-on-a-header design.
  1. Schematic using Max5457.
    2P2T switch used to activate shutdown feature of pot.
  2. Component placement
  3. top wiring/trace layer
  4. bottom wiring/trace layer (only one jumper)
  5. board-to-board wiring
    left edge: buttons, mode indicator, and (on/off+shutdown) toggle switch
    top right: MAX5457 and related components
    bottom right: original pot. foot print
Instead of everything sitting on one PCB, it is broken into two smaller PCBs so that the buttons can be postioned more easily. or wired individually. The push/mom. buttons are from the header to ground. The LED is from the header to VCC. The toggle switch is both (a) from the header to VCC or GND, and (b) open/closed for the original pot. footprint.

tomas02
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Joined:Tue Nov 09, 2010 12:47 am

Re: Replace analog pot with digital pot?

Post by tomas02 » Sat May 14, 2011 5:04 am

Thank you so much for all the work youve put into this snowcat
do you know where i could get a pcb like this made in NZ
as i dont have the equipment available to make this.
Thanks

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