Always power up CR?

[wmcelderry]

Hi,

1st up: Thanks for making a great product.

Summary:
I would like a CR (R3 mk2) to start whenever it is powered.  Can you suggest any easy modification to do that?


Details:
I'm intending to use a CR in a test-rig for testing production devices' power consumption to ensure the DUT is within spec prior to shipping.
To that end, I want the CR to power up automatically and remain powered.  Being a software developer, I'm more than happy to modify your source code (thanks again for that too!), but I don't think this is possible with source changes alone?

While I'm less familiar with hardware I've muddled through to identify the MOSFET between Vbus and Vin as the likely modification point: short it so Vbus is shorted to Vin, and I think it will always be on.  (I've tested with momentary shorting and it works and doesn't seem to suffer for it).

I do not see any down side in either (1) leaving the MOSFET or (2) removing it from the board.

A) Can anyone else see a down side of either modification (1) or (2)?
B) Is there a 'better' solution?


Thanks!

Will.

P.S.  Is there a reason that the component designations are not on the board or schematic?  It makes it hard to discuss modifications like this...

[Felix]

After a quick POC test I just did, on R2 you can short the two pads shown below and as soon as battery or USB is plugged in the CR will turn ON and stay ON.



There is no way to do this in firmware, unless you first power up the unit from the power button and then disable AUTO-OFF function.
I would also say hardware user modifications like this one are not encouraged or endorsed or warrantied in any way, for obvious reasons, hence no compelling reason to fill the (otherwise pretty) SMD side with silkscreen designators.

[wmcelderry]

Hi Felix,

Thanks for the feedback, that's just the place I was suspecting.
Totally understand that it's not "as it's maker designed it", so I certainly wouldn't be sending it back if it breaks (more likely order another!)

It is a strength of OSHW that I can even make a guess at the fix, and it makes it much better than the closed-source equivalent IMO, so thanks again!

Finally: I understand the desire to keep the silk screen minimal - it certainly is pleasing on the eye!

All the best,

Will.

[bigjosh]

How about on most recent REV?

Thanks,
josh

[Felix]

Should be all the same, power section was not modified.

[bigjosh]

Got it!

Layout on my R3Mk5 was slightly different than above. Here is what the patch looks like...



Works great.

Maybe a solder jumper here if you ever are making changes nearby?

Thanks!

-josh

[Felix]

Thanks for sharing your mod. Most fluxes are good but I would advise cleaning the flux up to avoid any potential corrosion.