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Help me find an odd USB cable.


ProDave
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We have an electric piano / keyboard that has a USB (midi) connection connected to a tablet.  It's a type B on one end (that's the original type B not one of the mini B variants) and a type C on the other end.  This one, bought from ebay

 

Image 1 - Type C USB to B Cable Cord for Printer Scanner DJ Controller Mixer Surface Go 1M

 

Now this works and the tablet communicates with the piano and it all works.

 

BUT neither end supplies power, so you have to unplug the tablet and plug that into a charger from time to time to charge it.

 

So what I would like is the same cable but with a branch off to a full size USB A plug that can plug into a USB charger and keep the tablet charged while in use.

 

But the only Y or branch USB cables I can find are two USB type A plugs which does not solve the problem.

 

Any ideas?

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Okay getting nowhere with this.

 

Most of the various Y / splitter cables say only one side can be used for data the other side is only for charging.  So I don't want to be buying something that does not work.

 

So I got to thinking,  Make my own.

 

I rummaged through my box of USB cables and found 3 cables, each of which had one of the plugs i wanted on one end.  Cut off the other unwanted end and stripped the bare end.

 

Now a typical USB cable is a 4 core cable, a data pair (white and green) and a power pair (red and black)

 

Attempt 1.  I connected the power pair of the tablet cable to the power pair of the USB charger cable, and connected the data pair of the tablet cable to the data pair of the piano cable.  No, that did not work, the tablet did not recognise when the pano was plugged in.

 

Attempt 2. Connected them all together, power pair and data pair.  No, that won't even work as a straight through cable piano to tablet, it just does not recognise it being plugged in.

 

So what am I doing wrong?

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For attempt 1. How did you know which of the data lines were D+ D-? Was it because they had the same colours? That might not be the case.

 

Was the Type-C cable you had in your junk box able to data connect your tablet to a PC for example? I mean, if you patched it back together would it work? Same logic applied to Type-B cable would establish that at least there are working data paths.

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Okay I did some more experimenting.

 

Just using 2 of my cables, the C type and the USB A type I joined them together to make one cable, and that worked as a single cable to connect my phone to my laptop and it worked for data and power.

 

I then added in the third cable, the B type, connecting just the cable screen and the data pair. leaving the power pair disconnected.

 

My cable then would not communicate between the laptop and the phone.

 

I have concluded what I am up against is transmission line effects with the branch probably causing an impedance mismatch and reflections and the USB protocol just not working.

 

I assumed the D+ and D- cable colours are wired to a standard and I did not fancy trying to reverse them to see.

 

The cables that work for power and not data usually only have one pair, the first C cable i chopped in half hoping to use turned out to only contain the red and black pair.  I do wish such a cable was somehow labelled to say power only.

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Okay I decided to have another go.

 

Having previously got a "cut and shut" type A to type C cable working (without introducing the power feed)  I decided to go back to basics and try just a cut and shut type B to type C cable.  So I just joined all 4 cores and the cable screen in individual soldered and sleeved joints.

 

And it did not work.

 

Well I know the C type cable I was using was good, so almost out of desperation I butchered another type B cable and tried that.  And that does not work either.

 

What am I doing wrong?  If I can't get a straight through cable working there is no hope of adding the power feed to it.  It would be unbelievable to have a second dud type B cable.

 

Any ideas?

 

EDIT to add, I have googled the pinout for a type B USB plug and can confirm the cable I am trying is connected to the correct colour code.

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49 minutes ago, ProDave said:

Okay I decided to have another go.

 

Having previously got a "cut and shut" type A to type C cable working (without introducing the power feed)  I decided to go back to basics and try just a cut and shut type B to type C cable.  So I just joined all 4 cores and the cable screen in individual soldered and sleeved joints.

 

And it did not work.

 

Well I know the C type cable I was using was good, so almost out of desperation I butchered another type B cable and tried that.  And that does not work either.

 

What am I doing wrong?  If I can't get a straight through cable working there is no hope of adding the power feed to it.  It would be unbelievable to have a second dud type B cable.

 

Any ideas?

 

I personally regard the USB standards as a 'hot mess'. You may be having USB on-the-go issues. Pull-up/pull-down resistors are added to D+/- inside USB plugs to assert the connection roles between host and peripherals. Usually you would need an OTG cable to connect a USB peripheral to a tablet. If you go back to the working cable A to C you hacked, measuring the resistance between data and power pins might shed some light on the problem you had with the direct connection to the type B.

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3 minutes ago, Radian said:

hot mess

Well known that the C connector is a quantum device.

Try and plug it in, it will not fit, turn 180°, still does not fit, turn 180° again, still does not fit, again, no, finally after 720° of turn, it fits.

Well known and understood quantum spin characteristic.

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34 minutes ago, Radian said:

 

I personally regard the USB standards as a 'hot mess'. You may be having USB on-the-go issues. Pull-up/pull-down resistors are added to D+/- inside USB plugs to assert the connection roles between host and peripherals. Usually you would need an OTG cable to connect a USB peripheral to a tablet. If you go back to the working cable A to C you hacked, measuring the resistance between data and power pins might shed some light on the problem you had with the direct connection to the type B.

That's an interesting read.  But it just adds confusion rather than settles anything.  But it probably indicates that USB OTG is the issue I am having.

 

The red herring here of course is my hacked USB A to C cable was tested with a computer at one end, so would not need the USB OTG capability to work, and thus the fact it did work is not a surprise.  So the issue I probably have is the USB C plug and cable I am trying does not have the extra pin for USB OTG connected as that was outside the scope of it's intended use from the doner cable it came from.

 

A quick test with a multimeter shows no pull up or down resistors anywhere but that is only testing on the USB A and B plugs, the pins of a USB C are simply too small to probe directly.

 

I think my next trial, will be to buy another identical cable to the USB B to C that I previously bought and works, and then carefully cut into that and splice in just the power connection from the USB A lead.  At least I will be starting with a working cable with all the necessary extra pins and connection for USB OTG.

 

So much for USB being "universal"

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I don't think you can do OTG and charge at the same time. I think OTG allows the tablet to power peripherals like an endoscope camera where as charging requires power to flow the other way.

 

Googling "OTG and charging at same time" finds mixed opinions as to the feasibility and this vid but I've not tried it..

 

https://youtu.be/Ld6LjVe-Xo0

 

Some comments say it worked for them, others that it didn't. Depends on phone/tablet.

 

 

Edited by Temp
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9 minutes ago, Temp said:

I don't think you can do OTG and charge at the same time. I think OTG allows the tablet to power peripherals like an endoscope camera where as charging requires power to flow the other way.

 

Googling "OTG and charging at same time" finds mixed opinions as to the feasibility and this vid but I've not tried it..

 

https://youtu.be/Ld6LjVe-Xo0

 

Some comments say it worked for them, others that it didn't. Depends on phone/tablet.

 

 

Thanks.  That's all very well but to do that hack I would be trying to find and work on a resolderable version of the even smaller C type plug.

 

I think that's the final nail in the coffin of this project.  It just shows the STUPIDITY of making devices with just one USB connector used for data and charging.  In the good old days, power cables were a separate connector to data cables.  This is what we call "progress"

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5 minutes ago, ProDave said:

Thanks.  That's all very well but to do that hack I would be trying to find and work on a resolderable version of the even smaller C type plug.

 

I think that's the final nail in the coffin of this project.  It just shows the STUPIDITY of making devices with just one USB connector used for data and charging.  In the good old days, power cables were a separate connector to data cables.  This is what we call "progress"

 

Get a big phone that supports wireless charging?

 

 

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1 hour ago, ProDave said:

That's all very well but to do that hack I would be trying to find and work on a resolderable version of the even smaller C type plug.

 

Adafruit USB C breakout

Top view of a Adafruit USB Type C Breakout Board above an 8-pin header.

 

 

Quote

The two 5.1K resistors on the CC1 pins indicate to the upstream port to provide 5V and up to 1.5A (whether the upstream can supply that much current depends on what you're connecting to.

 

If you desolder those then you might be able to get the tablet to charge from the 5V pins but this may override OTG. At least you could experiment a little further 

 

Just put 'USB Type C Breakout Board' into your preferred online marketplace.

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