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ADC input impedance

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ADC input impedance

Chris Whittenburg

Can someone with access to the Overo schematic verify there isn't any additional circuitry on the ADC input lines going to the PMIC?  It seems like I'm seeing an unexpected loading on ADCIN3 thru 6, and it isn't there on ADCIN2 or ADCIN7.  It's almost like a 2K pull-down?

Thanks.


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Re: ADC input impedance

Ash Charles
Hi Chris,

I can confirm that there is no additional circuitry on the ADC
lines---they go directly from the PMIC to the board-to-board header.
Note though that ADCIN[3456] are multiplexed signals which will be
tied low when the SEL_MADC_MCPC bit in the CARKIT_ANA_CTRL register is
cleared to 0.

--Ash

On Sun, Dec 29, 2013 at 4:01 PM, Chris Whittenburg
<[hidden email]> wrote:

>
> Can someone with access to the Overo schematic verify there isn't any
> additional circuitry on the ADC input lines going to the PMIC?  It seems
> like I'm seeing an unexpected loading on ADCIN3 thru 6, and it isn't there
> on ADCIN2 or ADCIN7.  It's almost like a 2K pull-down?
>
> Thanks.
>
>
> ------------------------------------------------------------------------------
> Rapidly troubleshoot problems before they affect your business. Most IT
> organizations don't have a clear picture of how application performance
> affects their revenue. With AppDynamics, you get 100% visibility into your
> Java,.NET, & PHP application. Start your 15-day FREE TRIAL of AppDynamics
> Pro!
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>

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Re: ADC input impedance

Chris Whittenburg

On Sun, Dec 29, 2013 at 3:47 PM, Ash Charles <[hidden email]> wrote:
Hi Chris,

I can confirm that there is no additional circuitry on the ADC
lines---they go directly from the PMIC to the board-to-board header.
Note though that ADCIN[3456] are multiplexed signals which will be
tied low when the SEL_MADC_MCPC bit in the CARKIT_ANA_CTRL register is
cleared to 0.

Thanks for the quick reply.  It looks like I'm running into the problem where usb3v1 is turned off, causing ADCIN3 thru 6 not to work properly.  On my palo35, if I plug something into the OTG port, and load something like g_ether, then they work fine.  Without doing both of those things, they are pulled down.

I see searching on the mailing list, that this was discussed before, and a patch was proposed in an attachment, but the attachment doesn't get archived, so I'm not able to try it out.  

Does anyone else have a quick patch to solve this?  I'm fine with usb3v1 always being active, if that is easy to do.

Thanks.
 

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Re: ADC input impedance

Scott Ellis
I have this patch in my repos.

https://github.com/Pansenti/meta-pansenti/blob/master/recipes-kernel/linux/linux-gumstix-3.5/twl4030-usb-adc36-enable.patch

I don't remember what it does ;-)  

And I don't remember writing it, so I must have grabbed it from this
mailing list.

It's in the repos of some working projects that use the ADCs,
so at least it shouldn't blow anything up.
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Re: ADC input impedance

Chris Whittenburg

On Tue, Dec 31, 2013 at 3:04 PM, Scott Ellis <[hidden email]> wrote:
I have this patch in my repos.

https://github.com/Pansenti/meta-pansenti/blob/master/recipes-kernel/linux/linux-gumstix-3.5/twl4030-usb-adc36-enable.patch

I don't remember what it does ;-)

And I don't remember writing it, so I must have grabbed it from this
mailing list.

Hi Scott,

Yup, I have that one, but I think there is one more issue as mentioned here:


I think commenting out this other line should fix it, but I haven't verified:


Thanks,
Chris


 

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Re: ADC input impedance

adam
Hi Chris, did you ever verify the comment out (line 391 in twl4030-usb.c) for this issue?

Thanks,

Adam


On Tue, Dec 31, 2013 at 1:23 PM, Chris Whittenburg [via Gumstix] <[hidden email]> wrote:

On Tue, Dec 31, 2013 at 3:04 PM, Scott Ellis <[hidden email]> wrote:
I have this patch in my repos.

https://github.com/Pansenti/meta-pansenti/blob/master/recipes-kernel/linux/linux-gumstix-3.5/twl4030-usb-adc36-enable.patch

I don't remember what it does ;-)

And I don't remember writing it, so I must have grabbed it from this
mailing list.

Hi Scott,

Yup, I have that one, but I think there is one more issue as mentioned here:


I think commenting out this other line should fix it, but I haven't verified:


Thanks,
Chris


 

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