External Adc Clock - which solder pads do what

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BeRenz
Posts: 6
Joined: Mon Aug 10, 2020 6:05 pm

External Adc Clock - which solder pads do what

Post by BeRenz » Mon Aug 10, 2020 6:39 pm

I'm trying to modify a 125-14 so that it accepts clock for it's adc over sata. Is is correct that I therefore need to solder the resistors to the pads which are closer to the sma connector?
https://redpitaya.readthedocs.io/en/lat ... xtADC.html is a bit confusing, as the layout shown does not seem to be identical to the current version.
There is a photo attached with the current resistor configuration. (Edit: It would be attached, but for some reason with only a single post without any attachments my "attachment quota has been reached")
Best
Benjamin

alex123go
Posts: 14
Joined: Mon May 04, 2020 4:46 pm

Re: External Adc Clock - which solder pads do what

Post by alex123go » Tue Aug 11, 2020 4:02 pm

Hello BeRenz,

We successfully modified our Red Pitayas to accept a clock from the GPIO E2 connector. While it's not exactly what you're looking for, some steps are similar.

First, you need to remove R25 and R26, which are under the heatsink (you can unsolder or cut the 0 Ohm resistor).

Secondly, you need to solder 2 of the 3 pins of both row on the bottom of the FPGA. We used small portion of wire to solder the pads together.

The zoom layout of R23,R24,R27,R28 makes it difficult to determine which is which, but by looking at the angled capacitor, you can see the position of the resistor.
  1. If you want to connect a clock from an external source via the GPIO E2 connecter, you need to solder the 2 pins closer to the SMAs connector : R23,R24 (https://imgur.com/a/qWZyvsx, I also could not add attachments)
  2. If you want to route the clock via the FPGA, you need to solder the 2 pins farther from the SMAs R27,R28 (I've never tried this, there might be some particularities that I'm not aware)
The sata connectors are connected directly to the FPGA, so I think option 2 is best for you.

Good luck

BeRenz
Posts: 6
Joined: Mon Aug 10, 2020 6:05 pm

Re: External Adc Clock - which solder pads do what

Post by BeRenz » Tue Aug 11, 2020 6:48 pm

Thank you for your quick answer, this helps me a lot. :)
Edit: 13.Aug.20 picture for reference
RedPitaya Resistors for extAdcClock:
https://imgur.com/a/Itj0smq

alex123go
Posts: 14
Joined: Mon May 04, 2020 4:46 pm

Re: External Adc Clock - which solder pads do what

Post by alex123go » Thu Aug 20, 2020 8:50 pm

You're welcome! :)

Did it worked?
I just learned that I'll have to do approximately the same thing for a project I have.

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