r/raspberry_pi • u/Technical-Coffee7286 • 3d ago
Community Insights Any idea why these points are bridged?
Any idea why these points are bridged?
Hi all,
I have some raspberry pi’s (about 10) I pulled from some old Covid temperature sensing check in kiosks. They’re 4B 8gb units. Each of them has these 2 wires bridging what seems to be the USBC port and the middle USBA stack. Is this accurate? If so, why? Just to run power to the USB ports?
Thanks!
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u/jojo9092 3d ago
They prob had issues with voltage sag on higher currents on those ports, it seems to just beef up the 5v lines to those ports.
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u/NightmareJoker2 3d ago
This is to enable back feeding of the 5V supply.
On old first gen Raspberry Pi A and B models you could plug an Arduino into the USB port and just apply power to the Arduino to power the Raspberry Pi. I have an OG Mr Beam open source laser cutter that did this. I’m not sure exactly but I think in the 2B or 3B they fixed the back feeding “issue”, and that requires using an extra power adapter and cable. The newer models can still be powered by the pins on the GPIO header, but it’s not nearly as convenient.
I suppose it was cheaper to solder some random junk wires instead of buying and plugging in a USB-A to USB-C cable.
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u/djchateau 3d ago
Why would you ever want to intentionally do that? That seems like that's asking for something to go wrong.
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u/NightmareJoker2 2d ago
Not really, a 5V potential is a 5V potential. Where this goes wrong is if you throw USB-PD in the mix (the Microsoft Display Dock HD-500 does not support this, and will blow a fuse that is difficult to replace, if you attach a USB-C compliant PD device and charger, like a MacBook, which it does work with as a port breakout adapter), the power source cannot handle supplying both devices with sufficient power (browns out) or you have differing potentials between the different 5V sources. In the latter case, back feeding from a single supply is actually the safer option, because otherwise, you’re back feeding where it is indeed unsafe (into the power supply and it’s capacitors).
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u/davestar2048 1d ago
Yes and no, it's out of USB spec at least. While convenient, it's better that newer Pi actually comply with USB specifications.
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u/JumpmasterRT 16h ago
It was about using what they had on hand. The use of the iPad as the touch screen seemed a bit weird to me so I did a little digging, 10” screens were going to have to be manufactured first but there were thousands of iPads laying around.
So yeah, for the pandemic, that’s what they did. They quickly modified what they had instead of waiting for the production of what they wanted.
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u/aqwmasterofDOOM 3d ago
Considering it’s soldered to the 5V power out pin on the USB port (from left to right in this image is 5V, data -, data +, then ground), I’m assuming trying to Jerry rig more power out of the USB A port
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u/User1539 3d ago
Powering it from a powered USB, so they don't have to run a second line to the proper port.
I've seen this before, and the explanation was 'I don't know if it's safe to just plug in a powered hub to power from the A port, so I did this'
I was just thinking about that since I have a similar situation. Is it safe to just plug in a powered hub?
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u/ventus1b 2d ago
Interesting question.
I think the hubs I have at home a) don’t power the bus master and b) don’t provide enough power for a RPi.
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u/TECHFOURNINE 3d ago
Possibly running more power to the usb-A ports unclear why unless they had all 4 ports using power hungry usb devices possibly long strings of lights or multiple usb nic's or the ports blew a fuse and this is how they powered those two ports
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u/planeturban 3d ago
Sounds about right. They probably had some power hungry devices connected to the USB-A port.
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u/Technical-Coffee7286 2d ago
That makes sense, they had some TPU accelerators and a FLIR sensor in there so I guess those need the extra boost? I posted the whole kit in the comments
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u/Technical-Coffee7286 2d ago
For those wondering, here’s the contents of the whole kiosk. The brand is Darcy, the kiosk is essentially this box and an iPad on a metal stand.
Raspberry Pi 4B 8gb
2 Coral TPU USB accelerators
FLIR Lepton 3.5 + FLIR PureThermal 2 USB module
Pi camera
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u/dglsfrsr 1d ago
That is so cool. How did you get your hands on those?
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u/Technical-Coffee7286 1d ago
They were in storage at the building I manage, leftover from Covid. According to my research they’re pretty much useless and irrelevant now as complete products so I tore them apart to sell off the individual components. Might keep a few pi’s though to set up some wall mounted terminal screens for some building automation I’m setting up
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u/JumpmasterRT 16h ago edited 16h ago
I have need of RPi Kiosks. Would you be willing to sell a few of them whole (or without the iPad)?
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u/richms 2d ago
There is a reason that the real raspi power adapters are specced at 5.2v, its so that you still get 5 at the A ports. If you are powering off something weaker then the A ports will be down in voltage and things not run. This was a bodge I have seen a few times to remove the switching and limiting from the power to those ports so devices will run on it. I have seen it on some USB cameras that would not run when the pi was powered off 5v
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u/Successful_Cod_8904 2d ago
Would this solve my issue with powerdrops when nvme and hdd are both on usb ports? Have offical power adapter connect to Pi4b
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u/No_Article_2436 6h ago
They are connected because they need to either communicate, or that is possibly a power wire.
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u/martinr7b 2d ago
As a person who did this exactly 2 days ago, this is to get rid of the voltage drop on the USB ports. I needed to power a USB DVD drive