MightyHat and Pi3 powerup issue (solved)

[probson]

Just thought I'd share this info if it helps anyone.
Power supply used is the Pi 5v 2.5amp. No other peripherals were attached to the Pi 3.
I had an issue where the MightyHat would reset when attempting to power-up the Pi 3 using the onboard On/Off button. The fix was to add a filter cap to the input of the mosfet switch. The value I used was 1000uf 6.3V. I did try 100uF, but this wasn't large enough and I only had these two values to hand.
There's a market outline on the MightyHat board(R3) underside for a cap, but it won't accommodate a cap of this physical size. A lower value should suffice though if needed.

Outcome, Pi 3 and MightyHat working great!!

[Felix]

Hi probson - thanks for sharing your solution and findings!
The part I'm not really following is this:

I had an issue where the MightyHat would reset when attempting to power-up the Pi 3 using the onboard On/Off button.

Could you possibly give more detail, how would it reset, after what interval?

[probson]

Hi Felix,

Hope this info is more useful.
On pressing the On/Off button on the Hat the LCD display and back-light would extinguish, as if you had removed power, and the then reinitialize as it does on first power-up. This happened every time I pressed the On/Off button.
The Hat worked okay when removed from the Pi 3.
With the Hat plugged back into the Pi 3, I measured the 5v line to the input side of the power mosfet and didn't observe any dip when pressing the On/Off button. This was using a DMM.
As a further test I shorted out the '5v on-link' on the Hat. When I applied power to the Hat, both the Hat and Pi 3 powered up okay.
I then decided to try adding a cap to the 5v line which resulted in a good result.

I probably should have said "appears" to reset as I didn't have a DSO to hand to be certain, nor a schematic of the Hat.

[Felix]

Okay, so everything is OFF when you press the power button (including the LCD etc) right?
Then when do they have a chance to turn ON then back off (reset)? I gather there must be some delay otherwise how do they reset before even being powered up?
That was my point of interest.

What is your power source? Just a battery (what is measaured voltage?)? Or is do you power from 5v?

To see dips you really need a scope and use a trigger. If the Hat tries to power a load that is too demanding, there would be a dip of a few ms to a few dozen ms, that's impossible to capture on a DDM except if it has a very fast sweep and a MIN-MAX mode that can capture that lowest voltage, still you could not see the actual waveform, just a number.

In the end whatever works will solve the issue and I did put the Capacitor pad just for this purpose, although generally it should not be needed. The cap is a reservoir that will charge before you power the Pi and will provide the needed boost till the booster can catch up with the demand.

[probson]

So much easier when you can see something, so have a look at this,
https://dl.dropboxusercontent.com/u/119565528/MHat%20powerup%20issue%20comp.mp4

The power supply is the genuine Pi power supply rated at 5.1v 2.5A. I also tried other another supply.

[Felix]

Ok I fully get it now
Thanks for the video.
The power surge cannot be met without the capacitor, that makes some sense. I might start including a capacitor in the kit...
So you're good now, you've solved the problem right?

[probson]

Yes, problem solved 

To add, I really like the MightyHat. It's a nice tidy solution and well throughout. Great work Felix.

[Felix]

Yes, problem solved 
To add, I really like the MightyHat. It's a nice tidy solution and well throughout. Great work Felix.

Awesome, really happy to hear that. Thanks for the feedback, much appreciated!

[[email protected]]

Felix  - I recently received my MightyHat, and just made it through the assembly pages, to find myself with an unexpected component, not mentioned anywhere in the assembly instructions.  A 1000uF capacitor.  While I appreciate that the cap was included, and is a fix for Pi3 + MightyHat not starting up cleanly, it would help the more neophyte of us if the assembly instructions could reflect the new component - or at least make mention of it.   
Obviously I found this thread, and that explains the part.   
Fantastic products and love the site.  -Mike

[Felix]

Hey Mike,
I think in most cases it's not even needed, maybe that's why I postponed or forgot to do it.
But I just added a little section in the assembly guide that shows this.
Thanks for the heads up,
-Felix