taketwo4you
Posts: 12
Joined: Wed Feb 05, 2014 11:46 pm

Powering B+ through a monitor's USB hub

Wed Jul 30, 2014 8:38 pm

Hello Everyone,

At work, we have been using Model B's combined with ViewSonic TD2220's(touchscreen monitors) for kiosks and they have been working great, except that the SD cards keep bending/warping. So I was very happy to see the B+ announcement and the move to microSD.

With the Model B's, we could power the Pi off of the TD2220's built-in USB hub. We would connect a USB to microUSB cable from the hub to the Pi's power, then plug a USB A to B cable from the Pi's USB to the hub's input. But with the B+'s we cannot, it just won't power on at all. I've confirmed that the B's were not getting backfed, rather they were getting power through the power cable. But I still think it's related to that.

It seems to me that with the B's once I made the "loop" the hub recognized that it was connected to a computer and powered itself(and therefore the Pi). But with the B+, it doesn't ever realize it's connected and stays powered off.

I'm not an EE, but what I think is happening is that the protection that was put in place to avoid backfeeding is also blocking this loop. It's possible that the loop was only possible because the B's started with some sort of backfeed "kick start".

So, what I'm looking for is if there's a way to bypass the protection, or trick the Pi into telling the monitor that it's powered on, or some other suggestion that would hopefully avoid purchasing a power supply for each kiosk(100+). I'm expecting to hear it's hopeless, but I'd gladly hear that there's a simple fix I was too stupid to realize.

Thanks for your time!

-Adam

drgeoff
Posts: 10215
Joined: Wed Jan 25, 2012 6:39 pm

Re: Powering B+ through a monitor's USB hub

Wed Jul 30, 2014 9:24 pm

Please confirm that my understanding is correct.

You connect a USB to micro-USB cable between a USB socket on the monitor and the RPi B+'s micro-USB power input. You connect HDMI cable between RPi and monitor. You power up and the B+ boots.

You power everything down and additionally connect a USB cable from one of the B+ USB ports to the monitor's USB "input". You power up and the B+ does not boot.

Also, other than providing power, do you need the hub function given that the RPi has 4 USB ports?

taketwo4you
Posts: 12
Joined: Wed Feb 05, 2014 11:46 pm

Re: Powering B+ through a monitor's USB hub

Wed Jul 30, 2014 10:10 pm

Thank you for your response.
You connect a USB to micro-USB cable between a USB socket on the monitor and the RPi B+'s micro-USB power input. You connect HDMI cable between RPi and monitor. You power up and the B+ boots.
This is only true if the USB Type B socket is connected to another, powered on, computer. This Type B socket is used for the touch controls and then additionally shares out the USB connection like a hub. If the Type B socket is not connected to anything, the Pi will not boot(the monitor powers down the Hub since it's not connected to anything).
You power everything down and additionally connect a USB cable from one of the B+ USB ports to the monitor's USB "input". You power up and the B+ does not boot.
Correct. If I have the monitor's Type B USB socket connected to one of the Pi's 4 Type A sockets, the Pi will not boot.
Also, other than providing power, do you need the hub function given that the RPi has 4 USB ports?
No. We are not using any other peripherals. We only use the one USB port.

Again, thank you for your response and let me know if I can clarify anything further for you.

shuckle
Posts: 565
Joined: Sun Aug 26, 2012 11:49 am
Location: Finland

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 6:05 am

I have the same problem with my monitor and old model B.
I can get it to work by first powering the B from external battery. I have the Raspi USB connected to the monitor USB input so that the monitor sees a computer and wakes up.
After Raspi has been booted, I can then connect monitor USB to Raspi micro USB to feed power from monitor top Raspi and close the external battery.
Stange that it works for you with old model B, but not with new B+. I might try what my B+ says in this setup.

phelum
Posts: 72
Joined: Thu Jul 17, 2014 7:05 am
Location: Sydney, AUS

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 12:45 pm

taketwo4you wrote: So, what I'm looking for is if there's a way to bypass the protection, or trick the Pi into telling the monitor that it's powered on, or some other suggestion that would hopefully avoid purchasing a power supply for each kiosk(100+). I'm expecting to hear it's hopeless, but I'd gladly hear that there's a simple fix I was too stupid to realize.
Hi Adam,

Yes, the power supply to the USB ports is different on the B+ and if you try to run a B+ with B software (one driver in particular) then the USB ports aren't powered at all. There is a regulator between the power rail and the USB power rail and this does stop backfeeding.

Can you try a USB cable with a splitter so that as well as going to the USB A socket then power wires also go the the micro-B socket that is normally connected to the power supply ?

Cheers,
Steven

PiGraham
Posts: 3710
Joined: Fri Jun 07, 2013 12:37 pm
Location: Waterlooville

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 12:59 pm

I have seen this sort of problem with Android TV sticks on a powered hub. The hub is shutdown until it detects a USB host, but your USB host is off until the hub turns on. Catch 22.
I found that a cheap powered hub works in the configuration most of the time.

Are you only using the hub to power the Pi? Have you tried powering the B+ direct from the TV USB port. The B+ is much more tolerant of power supply voltage and draws less power than the B so you might get away without a hub.

User avatar
RaTTuS
Posts: 10531
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK
Contact: Twitter YouTube

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 1:19 pm

or power the B+ via the GPIO
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

phelum
Posts: 72
Joined: Thu Jul 17, 2014 7:05 am
Location: Sydney, AUS

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 1:24 pm

RaTTuS wrote:or power the B+ via the GPIO
This sounds like a good alternative, especially to straining a micro-B plug and cable with current exceeding what they're designed for. Are the 5V GPIO pins directly connected to the power rail ?

Thanks,
Steven

User avatar
RaTTuS
Posts: 10531
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK
Contact: Twitter YouTube

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 1:40 pm

phelum wrote:
RaTTuS wrote:or power the B+ via the GPIO
This sounds like a good alternative, especially to straining a micro-B plug and cable with current exceeding what they're designed for. Are the 5V GPIO pins directly connected to the power rail ?

Thanks,
Steven
5V is connected to the power rail - it bypasses the on board fuse though
the micro USB plug is rated at 1A / pin and 1.8A / pin on 1 & 5 [which is the power]

[quick edit]
askully - 1.8A if if the other pins are limited to .5A - but in the power situation that is covered
How To ask Questions :- http://www.catb.org/esr/faqs/smart-questions.html
WARNING - some parts of this post may be erroneous YMMV

1QC43qbL5FySu2Pi51vGqKqxy3UiJgukSX
Covfefe

taketwo4you
Posts: 12
Joined: Wed Feb 05, 2014 11:46 pm

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 3:11 pm

phelum wrote: Yes, the power supply to the USB ports is different on the B+ and if you try to run a B+ with B software (one driver in particular) then the USB ports aren't powered at all. There is a regulator between the power rail and the USB power rail and this does stop backfeeding.
I did find this out. I was unable to get the B+ to boot with B software at all, until did an apt-get update/upgrade and rpi-update. But I have tried powering the B+ through the monitor with the updated software, newly downloaded Raspian, and NOOBs lite, none will power with my described setup(all are working using an external power supply, 2A phone charger).
phelum wrote:Can you try a USB cable with a splitter so that as well as going to the USB A socket then power wires also go the the micro-B socket that is normally connected to the power supply ?
I'm not exactly sure what you mean by this. Do you have a link to an example splitter?

Here's a diagram of what I'm trying to do. This works with Model B Pi's, but is not working with the Model B+.

Code: Select all

|\
| |
| |
| |
|M|---USB "TYPE B" HUB INPUT----------  <--"Printer" USB cable
|O|                                  |
|N|                                  | 
|I|                                  | 1 of 4(2) Pi "TYPE A" sockets  
|T|                                  ____________ 
|O|                                  |           |
|R|                                  |           |
| |                                  |           |
| |                                  |     PI    |
| |                                  |           |
| |--USB "TYPE A" HUB SOCKET---------|           |
| |                            ^     |___________|
|/                             |    Pi's microUSB power socket
            USB to microUSB cable

Also, to clarify, I'm not using any additional Hubs, only the built in hub in the monitor itself.
RaTTuS wrote:or power the B+ via the GPIO
Where would you suggest getting the power from? If I could piece together a little "starter" that would power the Pi USB ports enough to turn on the monitor's hub and then turn off and let the hub power the Pi, that might be ok. Something like a battery and button connected to jumpers.

User avatar
Burngate
Posts: 6188
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore
Contact: Website

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 4:40 pm

If the monitor's hub reacts as you describe, there seems to be a couple of things to try.

One is to dive into the monitor, and wire across from its A port to its B port - it'll provide its own power and think it's connected.
Another is to do the same thing on the Pi, from the uUSB power input to its USB A ports.

It may not be necessary to use a piece of wire, depending on how much current the monitor draws on its input - a small resistor might do.
Though since that power will appear on the Pi's other ports, anything attached there will sink current.

If doing it inside the monitor, disconnecting the power to the port ("cutting the red wire") might be wise

That's purely theoretical since I don't have one of these monitors.

phelum
Posts: 72
Joined: Thu Jul 17, 2014 7:05 am
Location: Sydney, AUS

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 8:56 pm

RaTTuS wrote: 5V is connected to the power rail - it bypasses the on board fuse though
the micro USB plug is rated at 1A / pin and 1.8A / pin on 1 & 5 [which is the power]

[quick edit]
askully - 1.8A if if the other pins are limited to .5A - but in the power situation that is covered
Thanks for these details. I've hit the problem (mentioned in this forum) that the wires in the USB-A to micro-B cable don't support the current required when I attach a USB HDD. This means I can't run the RPi using my master power supply which has USB-A sockets. I'll make a cable that connects to the GPIO pins and use this instead. Sounds much easier than hacking a micro-B plug and soldering wires to it.

Thanks,
Steven

phelum
Posts: 72
Joined: Thu Jul 17, 2014 7:05 am
Location: Sydney, AUS

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 9:07 pm

taketwo4you wrote:
phelum wrote:Can you try a USB cable with a splitter so that as well as going to the USB A socket then power wires also go the the micro-B socket that is normally connected to the power supply ?
I'm not exactly sure what you mean by this. Do you have a link to an example splitter?
I don't know of any ready-made product. I was thinking of connecting the power lines in your cable that connects to the RPi USB port to the micro-B power socket. This would probably involve modifying a cable.

As an alternative why not leave your cable from the monitor to the RPi USB-A socket and connect a short cable from one of the other RPi USB-A sockets to the RPi micro-B socket. All the power and ground pins on the USB-A sockets are tied together. Then power from the monitor will get to the RPI USB-A sockets and from there it will get to the micro-B socket and hopefully the B+ will power up like the B does.

Cheers,
Steven

taketwo4you
Posts: 12
Joined: Wed Feb 05, 2014 11:46 pm

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 9:20 pm

phelum wrote:
taketwo4you wrote:
phelum wrote:Can you try a USB cable with a splitter so that as well as going to the USB A socket then power wires also go the the micro-B socket that is normally connected to the power supply ?
I'm not exactly sure what you mean by this. Do you have a link to an example splitter?
I don't know of any ready-made product. I was thinking of connecting the power lines in your cable that connects to the RPi USB port to the micro-B power socket. This would probably involve modifying a cable.

As an alternative why not leave your cable from the monitor to the RPi USB-A socket and connect a short cable from one of the other RPi USB-A sockets to the RPi micro-B socket. All the power and ground pins on the USB-A sockets are tied together. Then power from the monitor will get to the RPI USB-A sockets and from there it will get to the micro-B socket and hopefully the B+ will power up like the B does.

Cheers,
Steven
I just tried this and no go. AFAIK the monitor's Type B port doesn't supply any power. I don't have any USB-A to USB-A cables to try adding a connection from the monitor's USB-A to one of the Pi's ports, but I'll try it as soon as I can find one.

phelum
Posts: 72
Joined: Thu Jul 17, 2014 7:05 am
Location: Sydney, AUS

Re: Powering B+ through a monitor's USB hub

Thu Jul 31, 2014 10:01 pm

taketwo4you wrote:
phelum wrote:I don't know of any ready-made product. I was thinking of connecting the power lines in your cable that connects to the RPi USB port to the micro-B power socket. This would probably involve modifying a cable.

As an alternative why not leave your cable from the monitor to the RPi USB-A socket and connect a short cable from one of the other RPi USB-A sockets to the RPi micro-B socket. All the power and ground pins on the USB-A sockets are tied together. Then power from the monitor will get to the RPI USB-A sockets and from there it will get to the micro-B socket and hopefully the B+ will power up like the B does.
I just tried this and no go. AFAIK the monitor's Type B port doesn't supply any power. I don't have any USB-A to USB-A cables to try adding a connection from the monitor's USB-A to one of the Pi's ports, but I'll try it as soon as I can find one.
Sorry that my idea didn't help. I'm not sure how your monitor USB-A to RPi USB-A will help because if the monitor USB-A was supplying power then your setup illustrated previously (monitor USB-A to micro-B) should have worked. Is this what you have with the RPI B that works ?

Does the monitor still work with an RPi model B ? If so, does the RPi B still boot if the cable to the monitor USB-B port is disconnected ? If yes to the first question and no to the second you might be able to get a B+ to emulate a B by connecting its power rail (e.g. the polyfuse or a 5V GPIO pin) to the USB ports power rail. If you don't want to hack the RPi B+ you could connect the monitor USB-A port to a USB-A port on the RPi and also connect a USB-A port on the RPi to the micro-B port on the RPi.

Hope this helps,
Steven

taketwo4you
Posts: 12
Joined: Wed Feb 05, 2014 11:46 pm

Re: Powering B+ through a monitor's USB hub

Fri Aug 01, 2014 3:07 pm

phelum wrote:
Sorry that my idea didn't help. I'm not sure how your monitor USB-A to RPi USB-A will help because if the monitor USB-A was supplying power then your setup illustrated previously (monitor USB-A to micro-B) should have worked. Is this what you have with the RPI B that works ?

Does the monitor still work with an RPi model B ? If so, does the RPi B still boot if the cable to the monitor USB-B port is disconnected ? If yes to the first question and no to the second you might be able to get a B+ to emulate a B by connecting its power rail (e.g. the polyfuse or a 5V GPIO pin) to the USB ports power rail. If you don't want to hack the RPi B+ you could connect the monitor USB-A port to a USB-A port on the RPi and also connect a USB-A port on the RPi to the micro-B port on the RPi.

Hope this helps,
Steven
In response to your first paragraph, the B does work as shown in my diagram, but the B+ does not.

As for the second paragraph, my answers are yes and then no. was able to find two different USB-A to USB-A cables, but one was one of those data transfer cables and the other was one from an external HDD enclosure that had a 3rd USB-A forking off on one end. Regardless, I tried both cables in every possible configuration I could think of and none of them worked.

I think the last option is to connect the power rails, which I will try because I'm curious, but I doubt will be a viable solution for our kiosk setups. I think I'll chat with my boss and we'll decide on either sticking with Model Bs or getting power supplies for the B+s.

I want to thank everyone for such quick responses and great ideas and info. I'll update with results of connecting the power rails when/if I get around to it.

neilf
Posts: 72
Joined: Sun Nov 11, 2012 8:14 am

Re: Powering B+ through a monitor's USB hub

Fri Aug 01, 2014 5:02 pm

For what it's worth, my B+ is working fine powered from my (Dell) monitor's hub, same as it did with a previous model B.

phelum
Posts: 72
Joined: Thu Jul 17, 2014 7:05 am
Location: Sydney, AUS

Re: Powering B+ through a monitor's USB hub

Fri Aug 01, 2014 7:41 pm

taketwo4you wrote: I think the last option is to connect the power rails, which I will try because I'm curious, but I doubt will be a viable solution for our kiosk setups. I think I'll chat with my boss and we'll decide on either sticking with Model Bs or getting power supplies for the B+s.
One thing I've noticed on the B+ is that on the micro-B socket pins 2, 3, and 4 are floating. Normally at least one of 2 and 3 are pulled high or low and this is how the host (the monitor USB-A socket) can tell that something is connected. Maybe it needs this before it will supply power.

Tying the power rails sounds promising but it shouldn't work because only USB-A sockets are meant to supply power. So I'd be surprised if the monitor B socket will do so.

Cheers,
Steven

taketwo4you
Posts: 12
Joined: Wed Feb 05, 2014 11:46 pm

Re: Powering B+ through a monitor's USB hub

Fri Aug 01, 2014 8:23 pm

neilf wrote:For what it's worth, my B+ is working fine powered from my (Dell) monitor's hub, same as it did with a previous model B.
I just tested this also. It will power off of a Dell. I may have to look into what Dell has to offer in the touchscreen market. Darn ViewSonic and their hubs that only power up when necessary!
phelum wrote:
taketwo4you wrote: I think the last option is to connect the power rails, which I will try because I'm curious, but I doubt will be a viable solution for our kiosk setups. I think I'll chat with my boss and we'll decide on either sticking with Model Bs or getting power supplies for the B+s.
One thing I've noticed on the B+ is that on the micro-B socket pins 2, 3, and 4 are floating. Normally at least one of 2 and 3 are pulled high or low and this is how the host (the monitor USB-A socket) can tell that something is connected. Maybe it needs this before it will supply power.

Tying the power rails sounds promising but it shouldn't work because only USB-A sockets are meant to supply power. So I'd be surprised if the monitor B socket will do so.

Cheers,
Steven
My idea was to somehow connect a jumper wire from one of the 4 USB-A ports on the Pi to the 5v GPIO pin. But like you said it shouldn't work. I'm still not sure how the Model B works, since the hub isn't powered unless it's connected to a working USB and the Pi's USB isn't "working" until the Pi is powered.

Any chance one of you guys could point me to the correct pin for the power rail on the Pi's USB ports? I have near zero experience with schematics and/or EE.

phelum
Posts: 72
Joined: Thu Jul 17, 2014 7:05 am
Location: Sydney, AUS

Re: Powering B+ through a monitor's USB hub

Sat Aug 02, 2014 10:04 am

taketwo4you wrote: My idea was to somehow connect a jumper wire from one of the 4 USB-A ports on the Pi to the 5v GPIO pin. But like you said it shouldn't work. I'm still not sure how the Model B works, since the hub isn't powered unless it's connected to a working USB and the Pi's USB isn't "working" until the Pi is powered.

Any chance one of you guys could point me to the correct pin for the power rail on the Pi's USB ports? I have near zero experience with schematics and/or EE.
Looking at the top of the sockets the 5V pin is the leftmost. If you're going to try connecting anything it might a good idea to check that the rightmost pin connects to ground (e.g. PP3 under the micro-B socket). With USB connectors the power pins are the outermost.

But I'm perplexed by your monitor. The USB specs say that only a USB-A socket should supply power. The host with a USB-A socket can detect when something is connected because the device will pull the data pins (the two inner ones) up. But the RPi B+ doesn't have the data pins connected to anything. So I'm thinking that the host (your monitor) doesn't power its 5V pin until it detects that something is connected. Do you have a USB mouse or HDD or something similar ? If so you could connect them to the USB-A socket and see if it supplies power.

The USB specs (wikipedia) say that the host has 15kohm resistors to pull the data pins low. For a device to be detected by pulling these pins high it must have power (how else could it do it ?) and since the host (your monitor) is the only thing with power then it would have to pulse the 5V pin in the USB-A socket high periodically and see if this pulse is reflected in the data pins. For the RPi B+ to satisfy this test it would need 1.5kohm resistors from pin 1 to pins 2 and 3 on the micro-B socket. But the RPi B (like the B+) doesn't have these so there must be something else.

Will your monitor USB-A socket power your RPi B if the only connection is from the USB-A on the monitor to the micro-B on the RPi B ? If so then I can't see why the B+ will be any different. Do you know that a B+ needs the latest software (a LAN9514 driver I think) before it will power the USB ports ?

Cheers,
Steven

User avatar
Burngate
Posts: 6188
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore
Contact: Website

Re: Powering B+ through a monitor's USB hub

Sat Aug 02, 2014 11:58 am

I'm not sure that's right.
On the B, at any rate, the data lines aren't pulled anywhere unless the chip does it (we've no information on the B+)

On neither B nor B+ are the micro-USB data-lines connected, so since the B worked, we can ignore those.
On the B, the chip isn't enabled until part way through the boot sequence, and the same is true on the B+, so the state of data lines seems to be unimportant.

The only difference between the B and the B+ before boot is that on the B+ there's no power on the 5v lines until after boot. On the B, power in = power out (apart from the polyfuse)

So for the monitor to be able to power the B but not the B+, it must be:
(a) putting power on the outputs
(b) looking for power on its input
(c) removing the power on the outputs iff there's no power on its input.

phelum
Posts: 72
Joined: Thu Jul 17, 2014 7:05 am
Location: Sydney, AUS

Re: Powering B+ through a monitor's USB hub

Sat Aug 02, 2014 12:53 pm

Burngate wrote: So for the monitor to be able to power the B but not the B+, it must be:
(a) putting power on the outputs
(b) looking for power on its input
(c) removing the power on the outputs iff there's no power on its input.
This certainly could be the case. I've just read through this thread (and realised I've asked questions that have already been answered) and noticed right at the start that the original working setup had the monitor USB-B port connected to a powered-up host. It makes sense that the hub downstream ports (the USB-A ports) will only be powered when there is an upstream link from the USB-B port. Maybe the monitor does pulse the downstream ports periodically (or maybe just once when first turned on) and this pulse on the USB-B port is enough to trick the monitor into enabling the downstream ports.

Maybe the OP (Adam ?) should connect the monitor USB-B port to a powered-up PC and see if this will enable the USB-A ports so they will provide power to the RPi. If this works for a model B then it should also work for a B+. If this works and the USB-B port has to be connected to the RPi (to supply touchscreen data) then a link from the RPi power to its USB-A socket 5V pin might help. I think this would make the B+ the same as a B in this respect.

Cheers,
Steven

taketwo4you
Posts: 12
Joined: Wed Feb 05, 2014 11:46 pm

Re: Powering B+ through a monitor's USB hub

Wed Aug 20, 2014 4:11 pm

Thanks again guys for all the discussion. Sorry for abandoning the thread for so long.
phelum wrote: Maybe the OP (Adam ?) should connect the monitor USB-B port to a powered-up PC and see if this will enable the USB-A ports so they will provide power to the RPi. If this works for a model B then it should also work for a B+.
This does work for both.
phelum wrote:If this works and the USB-B port has to be connected to the RPi (to supply touchscreen data)
This is required.
phelum wrote:...then a link from the RPi power to its USB-A socket 5V pin might help. I think this would make the B+ the same as a B in this respect.
I'm willing to try this, but need more guidance. I've got a soldering iron and wires stripped from Cat5e cable, but that's about it for supplies(however, I do have a RadioShack just down the road). If someone is willing to either make pictures or give me labeled solder points, I'll try this, just as a proof. But at this point, if I'd need to solder each Pi, I don't think this will be a usable solution for our project.

If this is where it ends, I thank you all!

phelum
Posts: 72
Joined: Thu Jul 17, 2014 7:05 am
Location: Sydney, AUS

Re: Powering B+ through a monitor's USB hub

Wed Aug 20, 2014 9:15 pm

taketwo4you wrote:
phelum wrote:...then a link from the RPi power to its USB-A socket 5V pin might help. I think this would make the B+ the same as a B in this respect.
I'm willing to try this, but need more guidance. I've got a soldering iron and wires stripped from Cat5e cable, but that's about it for supplies(however, I do have a RadioShack just down the road). If someone is willing to either make pictures or give me labeled solder points, I'll try this, just as a proof. But at this point, if I'd need to solder each Pi, I don't think this will be a usable solution for our project.
Hi Adam,
Your very pertinent comment about having to modify each Pi makes my suggestion academic at best. So I wouldn't risk wrecking the Pi unless you really want to try it. I don't think it should work anyway because the USB-B port shouldn't supply power. Since you say a Pi B works I'm guessing there is a power pulse when the monitor is first switched on. One test to check this theory would be to connect one USB-A port on the monitor to the B+ micro-B port (to power the B+) and connect another USB-A port on the monitor to the USB-B port on the monitor. If you then power on the monitor and the B+ boots it would verify the theory.

Might be better to just buy model Bs while they're still available.

Cheers,
Steven

Return to “Troubleshooting”