DFansler
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Boot problems with two USB touchscreens

Mon Sep 20, 2021 11:18 pm

I have built a dual touch screen pod with a raspberry pi 4 running OpenCPN. I have a USB GPS, USB wireless keyboard and the two USB touchscreens. The problem is that if the touch screens are plugged in on boot - the RPI never boots. Unplug the touch screens and the RPI boots.
Is there a way to disable the USB ports when shutting down a RPI and then turning them back on after the boot has completed?

Unplugging the touch screens is not an option since they are inside a sealed pod.

Kind regards,
David

aBUGSworstnightmare
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Re: Boot problems with two USB touchscreens

Tue Sep 21, 2021 6:14 am

Please provide more details on your setup, i.e. which touchscreens we are talking about.

Is it correct understanding your Pi boots with one of them connected, but not with both?

6by9
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
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Re: Boot problems with two USB touchscreens

Tue Sep 21, 2021 8:21 am

Potentially the touchscreens are breaking the USB spec and backpowering the host, and that could cause the Pi to not boot as the power sequencing is then wrong.
You could try connecting them via a USB hub as a test.
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DFansler
Posts: 16
Joined: Sun Aug 31, 2014 12:14 pm
Location: North Carolina, USA
Contact: Website

Re: Boot problems with two USB touchscreens

Tue Sep 21, 2021 2:55 pm

Thanks for the replies.

It will not boot with either one of the touch screens plugged in. I have three 12vdc to 5vdc power supplies in the unit, one for the RPI and one each for the two touch screens. I have unit sealed at this point for it’s first outing starting tomorrow, so I will try the usb hub once I return.

The touch screens are found on eBay if you do a search on “ 13.3" Capacitive Touch Screen LCD TFT Display HDMI Monitor for Raspberry Pi 3 4”, listed at $139. They are actually nice monitors, very thin in an aluminum case.

The power supplies are from Amazon, search for “ UCTRONICS DC 6V 9V 12V 24V to DC 5V 5A Buck Converter Module, 9-36V Step Down to USB 5V Transformer Dual Output Voltage Regulator Board [2 Pack]” at $14.99 for a pair. Their output is 5vdc @ 6a, which is far greater than the 8w (1.6a@5v) or the 5v@3a wall power supply included with the display.


Kind regards,
David

DFansler
Posts: 16
Joined: Sun Aug 31, 2014 12:14 pm
Location: North Carolina, USA
Contact: Website

Re: Boot problems with two USB touchscreens

Fri Oct 01, 2021 1:20 am

I am back from my trip with the two touch screen pod running openCPN - overall the performance was great - the radar was well defined and the charts were excellent. I did discover that the carbon fiber enclosure I built was also an excellent blocker of radio signals. The GPS I had in the enclosure would not work when totally enclosed - hanging it outside was a minor thing. WIFI was also dead on the RPI (also in the enclosure).

Otherwise all was well - except for the touch screen problem. I ordered a powered USB hub once I got back, and tried it tonight. The touch screens no longer halt the boot up of the RPI. My many thanks for the suggestion.

Kind regards,
David

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