User avatar
eried
Posts: 89
Joined: Mon Apr 15, 2013 2:11 am
Location: Chile

pi zero w test pads for extra USB [solved]

Thu Jul 06, 2017 9:33 pm

Hi everyone,

I am trying to add an extra usb port for connecting and arduino using the back test pads in the zero w but sometimes when I plug the arduino the pi sometimes reboots itself.

Is that "extra" usb usable? Do I need extra circuitry?

Thanks
My website: www.ried.cl

User avatar
Paeryn
Posts: 2735
Joined: Wed Nov 23, 2011 1:10 am
Location: Sheffield, England

Re: pi zero w test pads for extra USB

Thu Jul 06, 2017 10:02 pm

The Pi Zero only has one USB port, to have more USB connections you need to connect it to a USB hub. I don't know what pads are under there but I suspect they are just connections to the pins in the USB socket. If you try to have two devices directly connected to the same port things aren't going to work.
She who travels light — forgot something.

User avatar
eried
Posts: 89
Joined: Mon Apr 15, 2013 2:11 am
Location: Chile

Re: pi zero w test pads for extra USB

Thu Jul 06, 2017 10:47 pm

Paeryn wrote:The Pi Zero only has one USB port, to have more USB connections you need to connect it to a USB hub. I don't know what pads are under there but I suspect they are just connections to the pins in the USB socket. If you try to have two devices directly connected to the same port things aren't going to work.
EDIT: maybe you are right and it is the same port... So, can I put a 10 uf cap between vcc and gnd to avois the reboots when hotplugging?

There is another usb, it actually works independent to the main already soldered one:
Image

But as I say, it is not 100% stable. Maybe for something permanent is perfect but for hotplugging seems to do something bad
My website: www.ried.cl

User avatar
davidcoton
Posts: 4243
Joined: Mon Sep 01, 2014 2:37 pm
Location: Cambridge, UK

Re: pi zero w test pads for extra USB

Thu Jul 06, 2017 11:37 pm

eried wrote: maybe you are right and it is the same port
FTFY. There is only one USB port. The test points are connected to it.
Don't get confused by the power connector which has no data lines.
eried wrote: can I put a 10 uf cap between vcc and gnd to avois the reboots when hotplugging?
Worth a try, but 10μF may not be enough -- indeed the simple design of the Pi0 means it may always be vulnerable to sudden USB loads. Adding relatively small capacitance at the socket relies on the inductance of the PCB tracks between the common 5V and the USB connector to prevent the Pi from crashing. What is actually needed is a current limit on the USB 5V output.
Signature retired

User avatar
Paeryn
Posts: 2735
Joined: Wed Nov 23, 2011 1:10 am
Location: Sheffield, England

Re: pi zero w test pads for extra USB

Thu Jul 06, 2017 11:49 pm

The SoC itself only has 1 USB port, the RPi1/2/3 all have a USB hub/lan chip connected to that port which provides the 4 (2 on the original RPi1) ports that are exposed. The Zero and Zero W don't have that hub chip.
I'd be very surprised if you managed to get two devices connected at the same time to the single port and have them working, USB isn't designed to work that way.
She who travels light — forgot something.

User avatar
eried
Posts: 89
Joined: Mon Apr 15, 2013 2:11 am
Location: Chile

Re: pi zero w test pads for extra USB

Fri Jul 07, 2017 6:34 am

davidcoton wrote:
eried wrote: maybe you are right and it is the same port
FTFY. There is only one USB port. The test points are connected to it.
Don't get confused by the power connector which has no data lines.
eried wrote: can I put a 10 uf cap between vcc and gnd to avois the reboots when hotplugging?
Worth a try, but 10μF may not be enough -- indeed the simple design of the Pi0 means it may always be vulnerable to sudden USB loads. Adding relatively small capacitance at the socket relies on the inductance of the PCB tracks between the common 5V and the USB connector to prevent the Pi from crashing. What is actually needed is a current limit on the USB 5V output.
Thanks but I am bypassing vcc too (connected directly to the source vcc) so I hope the cap works. Adding more capacitance I think is going to bring another undesired side effect
My website: www.ried.cl

fruitoftheloom
Posts: 21039
Joined: Tue Mar 25, 2014 12:40 pm
Location: Delightful Dorset

Re: pi zero w test pads for extra USB

Fri Jul 07, 2017 6:50 am

eried wrote:
davidcoton wrote:
eried wrote: maybe you are right and it is the same port
FTFY. There is only one USB port. The test points are connected to it.
Don't get confused by the power connector which has no data lines.
eried wrote: can I put a 10 uf cap between vcc and gnd to avois the reboots when hotplugging?
Worth a try, but 10μF may not be enough -- indeed the simple design of the Pi0 means it may always be vulnerable to sudden USB loads. Adding relatively small capacitance at the socket relies on the inductance of the PCB tracks between the common 5V and the USB connector to prevent the Pi from crashing. What is actually needed is a current limit on the USB 5V output.
Thanks but I am bypassing vcc too (connected directly to the source vcc) so I hope the cap works. Adding more capacitance I think is going to bring another undesired side effect
The RPi Zero has a single USB BUS, you can not connect 2 devices as USB works on Master Slave principal it will not be able to I/O to both devices....
Retired disgracefully.....
This at present is my daily "computer" https://www.asus.com/us/Chrome-Devices/Chromebit-CS10/

User avatar
eried
Posts: 89
Joined: Mon Apr 15, 2013 2:11 am
Location: Chile

Re: pi zero w test pads for extra USB

Fri Jul 07, 2017 9:32 am

fruitoftheloom wrote: The RPi Zero has a single USB BUS, you can not connect 2 devices as USB works on Master Slave principal it will not be able to I/O to both devices....
I see... the main issue is that the pi reboots sometimes when plugging a device :/
My website: www.ried.cl

User avatar
RaTTuS
Posts: 10498
Joined: Tue Nov 29, 2011 11:12 am
Location: North West UK
Contact: Twitter YouTube

Re: pi zero w test pads for extra USB

Fri Jul 07, 2017 9:33 am

eried wrote:
fruitoftheloom wrote: The RPi Zero has a single USB BUS, you can not connect 2 devices as USB works on Master Slave principal it will not be able to I/O to both devices....
I see... the main issue is that the pi reboots sometimes when plugging a device :/
power surge - don't hot plug , or have a better PSU -
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

User avatar
elkberry
Posts: 167
Joined: Wed Dec 28, 2016 9:21 pm

Re: pi zero w test pads for extra USB

Fri Jul 07, 2017 5:28 pm

I'm seeing the same hotplug reboot problems, with the official 2.5A power supply connected to the pwr-in micro USB connector. So a better power supply may not help, unless powering via the extension connector?
From ZX81 to Raspberry Pi, but wait ... where's the 7805 gone?

User avatar
Burngate
Posts: 6089
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore
Contact: Website

Re: pi zero w test pads for extra USB

Fri Jul 07, 2017 5:40 pm

eried wrote:
davidcoton wrote:
eried wrote: can I put a 10 uf cap between vcc and gnd to avois the reboots when hotplugging?
Worth a try, but 10μF may not be enough -- indeed the simple design of the Pi0 means it may always be vulnerable to sudden USB loads. Adding relatively small capacitance at the socket relies on the inductance of the PCB tracks between the common 5V and the USB connector to prevent the Pi from crashing. What is actually needed is a current limit on the USB 5V output.
Thanks but I am bypassing vcc too (connected directly to the source vcc) so I hope the cap works. Adding more capacitance I think is going to bring another undesired side effect
eried wrote:I see... the main issue is that the pi reboots sometimes when plugging a device :/
There's already 47μF on the incoming 5v (C1) so 10μF is unlikely to make much difference.

User avatar
eried
Posts: 89
Joined: Mon Apr 15, 2013 2:11 am
Location: Chile

Re: pi zero w test pads for extra USB

Sat Jul 08, 2017 8:00 pm

elkberry wrote:I'm seeing the same hotplug reboot problems, with the official 2.5A power supply connected to the pwr-in micro USB connector. So a better power supply may not help, unless powering via the extension connector?
Is you inductor cracked? I discovered that mine is, so maybe that is the source of the problems. I am going to try to glue it in place and try again
My website: www.ried.cl

alphanumeric
Posts: 2138
Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: pi zero w test pads for extra USB

Sat Jul 08, 2017 8:54 pm

elkberry wrote:I'm seeing the same hotplug reboot problems, with the official 2.5A power supply connected to the pwr-in micro USB connector. So a better power supply may not help, unless powering via the extension connector?
Ditto, seeing the same thing here with the same PS.

drgeoff
Posts: 9912
Joined: Wed Jan 25, 2012 6:39 pm

Re: pi zero w test pads for extra USB

Sat Jul 08, 2017 9:54 pm

Hot-plugging in any USB device which has a capacitor on its power lines effectively puts a momentary short circuit across the 5 volt pins of the USB socket. Exactly what happens to the 5 volt rail on the Zero(W) depends in a complex way on many factors including but not limited to the characteristics of the capacitor on the device, the characteristics of capacitor(s) on the host, the characteristics of the PSU feeding the host, the resistances and inductances in both +5v and ground connections between all those capacitors and the PSU.

And then the impact on the Zero(W) of whatever happens to the 5 volt rail is a further complex dependency on the characteristics of the Broadcom SoC and the DC-DC converters supplying the other rails from the 5 volt one.

I take the easy option of not hot-plugging. :)

dgordon42
Posts: 764
Joined: Tue Aug 13, 2013 6:55 pm
Location: Dublin, Ireland

Re: pi zero w test pads for extra USB

Sun Jul 09, 2017 1:50 pm

It's worth noting that hot plugging USB devices to the original model A and B Pi's also caused them to crash & reboot. The model B+ (and later models) have extra power management circuitry in the 5V USB power supply to allow hot plugging of USB devices, among other things.
This USB power management circuitry is NOT present in the Zero models (to save cost), so it's not surprising that hot plugging USB devices causes them to crash & reboot.

Hope this helps,
Dave.

User avatar
eried
Posts: 89
Joined: Mon Apr 15, 2013 2:11 am
Location: Chile

Re: pi zero w test pads for extra USB

Sun Jul 09, 2017 3:17 pm

dgordon42 wrote:It's worth noting that hot plugging USB devices to the original model A and B Pi's also caused them to crash & reboot. The model B+ (and later models) have extra power management circuitry in the 5V USB power supply to allow hot plugging of USB devices, among other things.
This USB power management circuitry is NOT present in the Zero models (to save cost), so it's not surprising that hot plugging USB devices causes them to crash & reboot.

Hope this helps,
Dave.
Thanks. Maybe I use a bigger cap to attenuate the reboots. The device I am plugging is fairly low power (110 mA)
My website: www.ried.cl

SeeGreatness
Posts: 12
Joined: Mon Feb 20, 2017 11:28 pm

Re: pi zero w test pads for extra USB

Sun Jul 09, 2017 8:04 pm

here is an amazing video that will explane some amazing things i know your trying to add a usb port (female) if im correct then this should also work just change the male to a female head.
https://www.youtube.com/watch?v=OU9e3jIqaBY

SeeGreatness
Posts: 12
Joined: Mon Feb 20, 2017 11:28 pm

Re: pi zero w test pads for extra USB

Sun Jul 09, 2017 8:06 pm

Paeryn wrote:The Pi Zero only has one USB port, to have more USB connections you need to connect it to a USB hub. I don't know what pads are under there but I suspect they are just connections to the pins in the USB socket. If you try to have two devices directly connected to the same port things aren't going to work.
that is correct the data will be combined together from the two devices

drgeoff
Posts: 9912
Joined: Wed Jan 25, 2012 6:39 pm

Re: pi zero w test pads for extra USB

Mon Jul 10, 2017 8:44 am

SeeGreatness wrote:
Paeryn wrote:The Pi Zero only has one USB port, to have more USB connections you need to connect it to a USB hub. I don't know what pads are under there but I suspect they are just connections to the pins in the USB socket. If you try to have two devices directly connected to the same port things aren't going to work.
that is correct the data will be combined together from the two devices
The physical data connections with the two devices will be combined. It is unlikely that meaningful data will be received from either of them.

drgeoff
Posts: 9912
Joined: Wed Jan 25, 2012 6:39 pm

Re: pi zero w test pads for extra USB

Mon Jul 10, 2017 1:16 pm

SeeGreatness wrote:here is an amazing video that will explane some amazing things
Other than the different physical form factor, there is nothing "amazing" that cannot be achieved by using an ordinary micro-USB to USB cable plugged in to the micro-USB data socket on a Zero(W).

User avatar
eried
Posts: 89
Joined: Mon Apr 15, 2013 2:11 am
Location: Chile

Re: pi zero w test pads for extra USB

Wed Jul 12, 2017 8:27 am

Just to close up the original question, there is only 1 USB port in the Zero W, but I did solved the issue about the reboots.

I wired the usb directly to the input and added a 227 uF capacitor (between VCC and GND) plus a 0.5 Ohm 1W resistor (input VCC to output VCC). The pi does not reboot now on hot plugging devices :lol: :lol: my dock is reliable now:
Image
My website: www.ried.cl

julyjim
Posts: 117
Joined: Tue Jan 31, 2017 5:04 am

Re: pi zero w test pads for extra USB [solved]

Fri May 18, 2018 10:50 pm

Please check USB specification and do not disseminate misleading information.
USB devices can share the DATA connection physically / in parallel - they negotiate / share the common data bus as necessary.
Of course they can work thru the hub in tree like configuration and then share the common bus electronically.
The are designed to be "hot swappable" with very strict "power consumption" and should not cause any "rebooting" problems. It is the initial "power up " which starts the internal "here I am " process to notify the "master". Rebooting the "master" is definitely indication of trouble.
Very easy to demonstrate on RPi 3B with multiple USB connections and limited power available from "the hub".

Return to “Troubleshooting”