White Wire Ground Fix for LidMode triggering and noise

[Bryan Mayland]

This should have gotten its own thread long ago but I kept forgetting to make it and then lost the post. If your HeaterMeter v4.1 constantly is going into and out of Lid Detect mode while the blower is on below 100%, it is probably due to noise on the ADC due to poor design of the HeaterMeter PCB. The v4.1.3 board from April 20th may not exhibit this any more due to an expanded ground plane.

Moving the ground feed point

Step 1: Remove the barrel jack and cut the 4 connections to the ground plane with a razor. You don't have to be gentle, just look and see the 4 shiny lines going in each direction and score them.



Step 2: Check continuity between that hole and any pin labeled Gnd (probe header or FTDI header, etc). You should get nothing.

Step 3: Resolder in the barrel jack and run a wire from the pin where you just cut the leads to the center pin of the 5V regulator. The regulator creates a good deal of noise itself due to driving the Pi. Model A Pis have less noise than Model B and they're $10 cheaper to boot.



My test setup has 2x of the standard blower. Using my lab power supply with the modified configuration, I got 0 noise at any blower percentage. However, I found it interesting that two blowers rated at 0.2A each pull greater than 1A combined (in pulses) when running at low speeds.

 

[Darren C.]

Will the white wire mod benefit those of us running the 4.0 boards?

 

[Steve_M]

Will the white wire mod benefit those of us running the 4.0 boards?

Nope. It's only needed for v4.1.[1-2]

 

[KellyMc]

Can someone elaborate on cutting the ground plane connections? I don't know that I see shiny lines. Am I just cutting through the top layer in those four directions around the pad?

 

[Steve_M]

Can someone elaborate on cutting the ground plane connections? I don't know that I see shiny lines. Am I just cutting through the top layer in those four directions around the pad?

I've added arrows to the image Bryan posted to show what you should be looking for. It's the 4 flat edges at 12,3,6 and 9 o-clock

Note: don't cut the ones that I have arrows pointing to, those are there just for reference as Bryan has already scraped them away on the one that needs it.

 

[Bryan Mayland]

Can someone elaborate on cutting the ground plane connections? I don't know that I see shiny lines. Am I just cutting through the top layer in those four directions around the pad?

If you look closely on the BOTTOM layer (the side with the most components on it) you should see that the gold circle has 4 tiny bumps headed out in each of the 4 directions. You need to cut the bumps before they get to the purple area, isolating that gold ring from the ground plane.

 

[Mike-in-DE]

Since I haven't built mine yet, should I just do this from the start, or only if I have problems with the standard build?

 

[Bryan Mayland]

I would do it before you build it, because the traces you have to cut are under the barrel jack. If you find you need to do it later, then you'll have to desolder it which takes longer than the whole operation would take. There's no harm that can come of this, unless of course you get cut happy and cut the power!

 

[KellyMc]

Wow, seems like this fix is a real cure-all.

I got this done and had everything, including the servo, running tonight.

The no pit probe connected at low fan speed issue is gone, of course.

But I also previously had really flaky power and pit probe connectivity, which I had attributed to odd-sized jacks or my old, damaged probe. If I jiggled them the wrong way, they would disconnect. They both seem rock solid now. Totally worth having that unsightly wire reaching across my board.

 

[Peter F]

I used a Dremel and a very fine engraving bit to cut the four lines, real easy to do.