1

This PCB is a small screen, a 5" screen/display .. If I were to turn it over you'd see a display

What is meant to be plugged into the USB connector labelled "Touch" on this screen?

(Excuse the fact that apparently it's on a fleece material, and not a good idea to put a PCB on a fleece).

enter image description here

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  • A touch-sensitive panel?
    – gronostaj
    Jul 15, 2022 at 8:51
  • Is there a model number written somewhere?
    – harrymc
    Jul 15, 2022 at 8:59
  • @gronostaj like a "touchpad"? Thing is also, is it the case that USB-A outputs 5V, most other USBs expect 5V. So if it were for a touchpad, then wouldn't it have to a a USB-A?
    – barlop
    Jul 15, 2022 at 9:02
  • @harrymc brand is Jun-Saxifragelec. They don't have a website but are on amazon and I am in contact with them/the manufacturer, so am waiting a response from them on a related matter but I will be asking them this question too.
    – barlop
    Jul 15, 2022 at 9:03

2 Answers 2

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If you connect this usb to a computer, it would allow touch controls.

Eg: This port is used to comminuciate touch capabilities of the screen. Usuaully this screen is an embedded screen on a device, and this wire is not shown to the user, but it connects internally to the pc so that it has an additional mouse so to speak.

note added by barlop

barlop: "so that connector would go to the computer and cause the device's panel to be both screen and touchpad?"

lpchip "yes , that's basically how it works."

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  • So is it a connector that sends 5V out (as opposed to expects 5V)? (quite unusual for a USB connector that isn't USB-A). From what I understand USB-A sends 5V. And non-USB-A is meant to expect/receive 5V.
    – barlop
    Jul 15, 2022 at 9:08
  • And so if somebody plugged a power in there where it is ;abelled touch, would it damage the device?
    – barlop
    Jul 15, 2022 at 9:11
  • No, its a connector like any normal USB plug that asks for 5V and communicates with the requester. Consider this port the same as the IN port of a usb hub. One port that you use to connect to your computer and give your computer extra capabilities. For that reason, you can also connect power to it, but I doubt that will do much. At least not damage the device.
    – LPChip
    Jul 15, 2022 at 9:24
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    @barlop it likely does not send out (or receive) 5V at all except to sense when something is connected. What it most likely does is appear to a host PC as a USB HID device such as a mouse with absolute screen coordinates akin to a graphics tablet.
    – Mokubai
    Jul 15, 2022 at 9:24
  • 1
    Yes, that's basically how it works.
    – LPChip
    Jul 15, 2022 at 10:52
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I'd say, see LPChip's answer.

But also, a Micro-USB female (or Micro USB B female rather), implicitly indicate that they need to receive power.

Below is some explanation as to why.

From what I understand , a thing with a USB socket, is either a host, or a device.

A host provides power. A device receives power.

USB started off with connectors of USB-A, and (Standard) USB-B.

USB-A female connectors send power(or relate to sending power, the circuitry behind them are meant to send power). Hosts have those. So computers have those. Or, a power source, battery based or a mains based thing with an ACDC adaptor and a USB-A female connector on it. So, a charger/power source, (Whether battery based, or mains based), that provides a USB-A socket. aka USB charger - battery or mains.

USB-B female connectors receive power. And are on devices e.g. printers.

Devices can also have male A connectors e.g. a Flash drive.

So long as no gender changes are used, there isn't much or perhaps isn't any, danger of connecting two power sources together.

A cable that is USB-A male both ends, is I understand to be, illegal, as per the USB spec. Such a thing could lead somebody to connect for example, a charger to a computer, and harm both.

Micro USB A is extremely rare and has a particular appearance. When anybody says Micro USB they would mean Micro USB B.

That connector is Micro USB.. So, Micro USB B. And female.

Things with USB connectors that aren't cables, usually have female connectors.. with few exceptions.. Flash drives are one that have a male A. And as mentioned , Male A would be receiving power anyway, as would a female B.

One of those devices that provides a load which can be used to test USB voltage and current numbers under load, that also often has a USB male A connector., that's consistent with it receiving power.

That Micro USB on that thing you have with a panel(which could double up as screen and touchpad), has a female B, which is for receiving power. So, the circuitry behind that connector acts as a device rather than a host.

It might also send data, so connect a computer to it rather than just a battery/ rather than just an ACDC w/USB.

I checked with the manufacturer, and they said that either of those connectors will provide power to the device. I haven't tested the touchpad aspect yet but what they say of the screen is the case.

I'd add.. USB-C can be host or device.. And is meant to phase out USB-A.

There is USB OTG.. so you can take a phone which typically acts like a device (requiring power), and the adaptor gives it a female-USB-A, and lets it act as a host, providing power, to a keyboard. That is still following the pattern of USB-A female providing power.

Note that there there is Micro USB B 2.0, and Micro USB B 3.0 That one is Micro USB B 2.0 The Micro USB B 3.0 was used on some stuff like I have some samsung portable hard drives 1TB,2TB, from a few years back. Apparently now they use USB C more.

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  • Notably, some Raspberry Pi boards have two type B connectors with completely opposite functions: one is for receiving power and possibly emulating a USB device, the other one for plugging in peripherals OTG-style.
    – gronostaj
    Jul 15, 2022 at 18:57
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    -1 because USB devices don't have to be provided power. It's a part of the negotiation, and a device can be self-powered (as printers, for example, are).
    – jaskij
    Jul 15, 2022 at 19:16
  • Also, most micro-USB connectors, nowadays, are almost always AB, meaning OTG. Properly, it should be micro B, but because of economies of scale companies just stick AB on everything and just always indicate device.
    – jaskij
    Jul 15, 2022 at 19:17
  • As for damaging devices if you connect two of them via a non-standard A to A cable... Any sane host should have reverse current protection. So this should not happen. Gender... shouldn't matter iirc, but pendrives are an interesting exception I'd need to look up
    – jaskij
    Jul 15, 2022 at 19:20
  • @jaskij thanks.. regarding where you write "a device can be self-powered (as printers, for example, are) <-- What is a self powered printer? The printer I have plugs in and turns off when unplugged.. Is a self powered printer one that has a battery built into it. And is thus more portable. And so, given the battery it has, if it receives power it's just to charge the battery, which may or may not need charging?
    – barlop
    Jul 16, 2022 at 1:29

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