FrankGould
Posts: 28
Joined: Mon Mar 12, 2018 2:00 pm

Raspberry Pi 3A+ Touchscreen Tablet Success

Thu Feb 28, 2019 4:01 pm

I would like to report a success story that might help others trying something similar. What I created from the parts list below is a battery operated Raspberry Pi (RPi) 3A+ with UPS HAT that allows the tablet to be mobile to navigate a similarly configured RPi rover. What I've written below is not a precise step-by-step problem solving report but is a paraphrase of multiple experiments to accomplish a successful prototype streaming real-time video.

Instead of details about my creation, I wanted to share a very important power problem I solved with a couple solutions I found during my tests. In the beginning with fresh hardware and battery, streaming video played satisfactorily from the camera on the rover. Over time, the UPS board would reboot during a reboot when plugged into wall power.

This indicated a low power failure during boot and was eventually remedied with two solutions: a double amp battery and switch to USB power from the RPi directly into the touchscreen micro USB port. In my initial tests, I wired the UPS 5V GPIO output power directly to the power input pins on the touchscreen/graphics driver board. The USB power fix was fine but the video stopped playing and would only display a frame every few seconds or so.

This is when the word serendipitous comes into play that I happened to find an instruction in the elinux.org web page (link below) regarding RPiconfig: max_usb_current=1. With this instruction in the /boot/config.txt file, the micro USB port now had sufficient power to run the streaming video near real-time performance. Why this was serendipitous was because I was looking for config.txt changes to control my HDMI monitor screen brightness with software. I just happened to be reading down the page and the max_usb_current caught my eyes.

https://elinux.org/RPiconfig#USB_Power

So, for anyone attempting to create a tablet similar to my prototype, be sure to power the touchscreen from the RPi's USB port and include max_usb_current=1 in the /boot/config.txt file. As mentioned above, below are the components I used to create my remote control/tablet prototype.

Raspberry Pi 3A+
RPi Official 7" Touchscreen
MakerFocus Raspi UPS HAT Board and 2500mAh Lithium Battery (extra)
uxcell® Power Supply DC 3.7V 5000mAh Li-Po Battery (replaces extra battery above)
RAYSUN 2 Pack 90 Degree Micro USB Male to USB 2.0 A Male - Right & Left Angle (only one needed)

Please give me any comments or questions you may have using the Post Reply button below. I am new to configuring hardware components to create a tablet and remote controlled device and have learned a lot from my online experience. This is an opportunity for me to share back with the community.

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Imperf3kt
Posts: 4675
Joined: Tue Jun 20, 2017 12:16 am
Location: Australia

Re: Raspberry Pi 3A+ Touchscreen Tablet Success

Thu Feb 28, 2019 8:07 pm

On a Pi3A+ that usb current setting does nothing since there is nothing to control it.
On a Pi2b or later, the default usb current is 1.2A, so setting it to 1.0 is actually further restricting it.

I think something else fixed your issue.
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52:4C:52:42:41

Rose tinted glasses are difficult to see through.

fruitoftheloom
Posts: 27225
Joined: Tue Mar 25, 2014 12:40 pm

Re: Raspberry Pi 3A+ Touchscreen Tablet Success

Thu Feb 28, 2019 8:26 pm

FrankGould wrote:
Thu Feb 28, 2019 4:01 pm
I would like to report a success story that might help others trying something similar. What I created from the parts list below is a battery operated Raspberry Pi (RPi) 3A+ with UPS HAT that allows the tablet to be mobile to navigate a similarly configured RPi rover. What I've written below is not a precise step-by-step problem solving report but is a paraphrase of multiple experiments to accomplish a successful prototype streaming real-time video.

Instead of details about my creation, I wanted to share a very important power problem I solved with a couple solutions I found during my tests. In the beginning with fresh hardware and battery, streaming video played satisfactorily from the camera on the rover. Over time, the UPS board would reboot during a reboot when plugged into wall power.

This indicated a low power failure during boot and was eventually remedied with two solutions: a double amp battery and switch to USB power from the RPi directly into the touchscreen micro USB port. In my initial tests, I wired the UPS 5V GPIO output power directly to the power input pins on the touchscreen/graphics driver board. The USB power fix was fine but the video stopped playing and would only display a frame every few seconds or so.

This is when the word serendipitous comes into play that I happened to find an instruction in the elinux.org web page (link below) regarding RPiconfig: max_usb_current=1. With this instruction in the /boot/config.txt file, the micro USB port now had sufficient power to run the streaming video near real-time performance. Why this was serendipitous was because I was looking for config.txt changes to control my HDMI monitor screen brightness with software. I just happened to be reading down the page and the max_usb_current caught my eyes.

https://elinux.org/RPiconfig#USB_Power

So, for anyone attempting to create a tablet similar to my prototype, be sure to power the touchscreen from the RPi's USB port and include max_usb_current=1 in the /boot/config.txt file. As mentioned above, below are the components I used to create my remote control/tablet prototype.

Raspberry Pi 3A+
RPi Official 7" Touchscreen
MakerFocus Raspi UPS HAT Board and 2500mAh Lithium Battery (extra)
uxcell® Power Supply DC 3.7V 5000mAh Li-Po Battery (replaces extra battery above)
RAYSUN 2 Pack 90 Degree Micro USB Male to USB 2.0 A Male - Right & Left Angle (only one needed)

Please give me any comments or questions you may have using the Post Reply button below. I am new to configuring hardware components to create a tablet and remote controlled device and have learned a lot from my online experience. This is an opportunity for me to share back with the community.

max_usb only applies to the Raspberry Pi 1B+ / 2B, absolutely useless on your board:

https://www.raspberrypi.org/documentati ... /#pi-power
Take what I advise as advice not the utopian holy grail, and it is gratis !!

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