USB Device with Data Pins ONLY?

[cluelessgenius]

not sure where to put this but this seemed the closest sub forum.

 

i got an arduino nano hooked up to apa102s as ambilight. and it works great BUT the nano is powered externally together with the strip and so i made a longer usb cable and only hooked up the data cables so i dont feed power from the usb port. only problem is the device isnt recognized. when using a normal cable it works fine. 

so does anyone know? des windows require power lines to be kooked up to recognize a usb device ? or maybe the nano requires power to the usb specifically ? 

 

[jaslion]

The arduino requires for there to be a power handshake or it won't even bother starting communication.

[Levent]

2 minutes ago, jaslion said:

The arduino requires for there to be a power handshake or it won't even bother starting communication.

D+, D- and a common ground are required, as long as arduino is powered by something else vcc+ isnt required. I too have couple of arduinos powered externally that I connect to my pc to flash them.

[mariushm]

You also sort of need a common ground between the devices, otherwise the signals would be hard to decode... so connect the ground wire at the very least. 

 

[jaslion]

3 minutes ago, Levent said:

D+, D- and a common ground are required, as long as arduino is powered by something else vcc+ isnt required. I too have couple of arduinos powered externally that I connect to my pc to flash them.

Oh so vcc isn't required? Neat. So basically 3/4 2.0 wires are needed :p.

[cluelessgenius]

5 minutes ago, Levent said:

D+, D- and a common ground are required, as long as arduino is powered by something else vcc+ isnt required. I too have couple of arduinos powered externally that I connect to my pc to flash them.

3 minutes ago, mariushm said:

You also sort of need a common ground between the devices, otherwise the signals would be hard to decode... so connect the ground wire at the very least. 

 

 

ahh ok so if i additionally hook up the ground wire, it should be detected?

[mariushm]

14 minutes ago, cluelessgenius said:

 

ahh ok so if i additionally hook up the ground wire, it should be detected?

it depends on the usb controller.  There's other rules like the usb device not being allowed to pull more than 100mA at startup and then it can negotiate more power, so there's a possibility the usb controller could ignore traffic if there's no power consumption on the port. 

I guess a simple solution would be to add a led or something to consume a tiny amount of power ... for example a red led and a 1k resistor in series with the led  would consume around (5v - 2v) / 1000  = 3mA of current ... that's probably enough to exceed some imaginary threshold in a usb controller if such exists, and low enough not to burn your eyes (a generic red led would be reasonably bright at only 3mA, good as a stand-by / on indicator)

 

[mariushm]

Just now, James Evens said:

I know people tried RS485 without a GND and are somewhat successful so interesting that USB 2.0 even in a clean environment requires GND.

 

For easy of installation:

Use a normal USB cable and power the APA102 externally. Don't forgett to connect the APA102 PSU ground to the arduino GND.

 

 

usb 1.1 has +/- 3.3v levels , usb 2.0 and higher has +/- 400mV levels on the data wires. 

 

RS485 has much wider voltage range, for ex 5v or -7v..12v  ... also transmitters usually do +/- 1.5v and receivers must receive at least +/- 200mV ... see design guide : https://www.ti.com/lit/an/slla272d/slla272d.pdf

Also see the note about common ground in the guide... rs 485 is designed for longer distances where ground differences can be much higher and can cause problems.

[cluelessgenius]

1 hour ago, James Evens said:

I know people tried RS485 without a GND and are somewhat successful so interesting that USB 2.0 even in a clean environment requires GND.

 

For easy of installation:

Use a normal USB cable and power the APA102 externally. Don't forgett to connect the APA102 PSU ground to the arduino GND.

 

sry i cant read your drawing, heres my current setup

 

 

[mariushm]

You could power your arduino board from computer with 5v and ground from USB, and connect just the ground from usb and separate power supply together. 

The led strips can have their own separate 5v power supply. 

[cluelessgenius]

11 minutes ago, mariushm said:

You could power your arduino board from computer with 5v and ground from USB, and connect just the ground from usb and separate power supply together. 

The led strips can have their own separate 5v power supply. 

well i already have it hooked up like this pretty neatly. could not just connect the usb ground from nano to pc ?

[cluelessgenius]

also heres a test i did with a normal usb cable 

im pretty happy with the result over all. little bit of color calibration to do when displaying white or very dark colors but yeah...

[Levent]

4 hours ago, cluelessgenius said:

well i already have it hooked up like this pretty neatly. could not just connect the usb ground from nano to pc ?

Yes, that is what we suggested up top. As long as your arduino is powered separately, all you need is data +, data- and ground connection on that USB cable.