We Keep Coding

Monitor USB for camera connection

I have a USB microscope camera and I would like to open the Windows 10 camera app automatically if the camera gets connected to a USB port. After checking that this isn't possible with Windows 10 at the settings level, I have decided to write a short C# program that monitors the USB ports for a camera device connection (and runs the camera display app).
As to the monitoring I haven't got a slightest clue where to begin. Needless to say that the monitoring program should be lean with respect to blocking ressources, because it would be running all the time. Can I simply obtain an event notification of USB connection? Do I have to expect problems with permissions?
And of course, suggestions for alternative approaches are welcome, if any. Note that I do not want to capture and display video from the camera myself, unless it is easier to do it that way instead of opening the existing camera app.

assuming the microscope is using the web-camera interface I would look for guides about how to enumerate and connect to web-cameras. I have found a few alternatives:
Media capture API
Aforge
Versatile WebCam
I had most success with versatile webcam, but if you just want to enumerate devices any of them should do. Aforge is probably the easiest to use.
You can then use a timer to check for devices, and do something if the microscope is connected.
If the microscope is not a webcamera you will need to refer to the camera documentation on how to enumerate devices.

USB-Serial Port stops working without any reason

I use as USB-SerialPort Converter for a Barcodereader. (Drivers for the converter are supplied on a CD -- company: digitus)
In my program (C#) I wait for SerialPortDataReceived-Events and proceed if I get values -- so far everything works fine.
The problem now is that I don't receive Data anymore sometimes.
The same readers and USB-RS232 converters as well as the same notebooks (lenovo, Win7) are used at 8 stations, but only at 2 of them I have this problem.
When I am in the situation that I do not receive Data when the reader read some, I can't see any problem. Windows says that the serial port is working fine.
But when I unplug the power supply of the reader and reconnect the COM-Port in my program it works again.
(And I do not think that the reader is the problem, because those readers are used a couple of hundred times in the company I work for)
So it must be the converter or the cooperation from the converter and the barcode reader!?
My next idea would be trying another converter, but is there any way to understand the cause?
Or did anybody have a similar problem?

Try disabling the "USB selective suspend" feature
Open Control Panel.
Click on Hardware and Sound.
Click on Power Options.
Click the Change plan settings link for the plan you're currently using. (If you change the settings on the power plan that isn't active, this won't work.)
Click the Change advanced power settings link.
Expand USB settings.
Expand USB selective suspend setting.
Select Disabled from the drop-down menu.
Click Apply.
Click OK.
If you're changing the settings on a laptop or tablet, you'll see two options: On Battery and Plugged in, so make sure to change those settings accordingly.
Once you complete these steps, Windows 10 will no longer power off USB devices connected to your computer, which can fix any problem you may have as a result of this feature.
While this guide focuses on Windows 10, USB selective suspend has been around for a long time, and you can use the same steps on machines running Windows 8.1 and Windows 7.
For more details check https://www.windowscentral.com/how-prevent-windows-10-turning-usb-devices#:~:text=When%20a%20USB%20device%20is,feature%20to%20fix%20the%20problem.&text=Windows%2010%20includes%20the%20USB,re%20not%20actively%20in%20use.

USB ports are terribly unreliable in this way. The only way to get a reliable serial.port is to use a PCI card or an Ethernet device server. You will never get a consistent connection through USB.
We get a bug reported in our serial port comms about one a month, and every single occurrence is due to someone using a USB to RS232 converter. As soon as we install better hardwarec the issue vanishes.

How to control my USB port using C# [duplicate]

This question already has answers here:
Power off an USB device in software on Windows
(5 answers)
Closed 9 years ago.
What I want to write is an application that would be able to access my USB port.
To control when to charge my phone and when not to. And perhaps with time I would like to extend the application to control light bulbs, fans and the television in my room.
I want to learn how to work this out rather than just copy some line of codes and paste. I wish for a quick and very simplified tutorial on this, I would be highly grateful (small language please, You all know am still learning :-)).
The exact job I want to achieve is just to make the port send out power when needed. That is it should be switched off and on using codes if possible.

It isn't possible to change the power status of a USB port from User mode code. It's not a .NET limitation, no user application can change the power status of a USB port. Actually, I think that the power state is controlled by the chipset itself and you can't turn it off without using a specialized chipset.
Besides, if your device short-circuited, you could burn your chipset and your motherboard.
The only (safe) solution is to use an external device that will control a relay to turn power on or off for your devices.
There are multiple answers to similar questions, eg Windows- Power off a USB device in Software
A good option is to use an external device like Arduino (or Netduino), .NET Gadgeteer or any number of external boards. Prices and capabilities vary of course.
If you want to build the device yourself, you can find numerous USB relays with a simple Google search
EDIT
Regarding serial ports, there is almost no relation at all between the two port types. Serial ports are not designed to provide power. You can use tricks to use a pin's voltage to power some external device, although this will lead to problems because there is not enough current to power most devices. Burning the chipset is another likely outcome.
A USB port on the other hand, is explicitly designed to provide power through specific wires which can't be controlled normally. This is why you can charge your phone from a desktop's USB port even if the machine has shut down.
EDIT 2: Sleep-and-charge ports
As Ben Voigt noted, not all USB ports allow charging while shutdown.
There are multiple port types that support charging. Charging ports provide more current than plain ports but shut down when the computer is switched off. Sleep-and-charge ports on the other hand can provide power even when the computer is off.

Alt-Tab pedal with an Arduino

I'm creating an Alt-Tab pedal with an Arduino. The idea is that the user will just press down on a pedal that will hit a button on the Arduino, and this would be the equivalent of hitting the ALT+TAB key (thereby allowing you to stealthily switch windows).
I'm also open to just minimizing the window.
The problem is, I'm not really sure how to go about this. Should I use a command that runs a batch file? Is there a command in C I can implement this with? I'm open to any suggestions.

SendKeys.Send("%{TAB}");
Or use SendInput() in a C program.

Based on the other answers, it sounds like you’re proposing to have the Arduino connected to the computer with USB and send a letter when the pedal is pushed, then have a program on the computer side receive that message and invoke Alt-Tab.
There’s a different way to do this: Teensy 2.0 is an Arduino variant based on the ATmega32U4 microcontroller. This is an AVR chip that has built-in USB support, instead of a serial port that’s translated to USB with a USB-serial bridge as you’ll find on an Arduino.
One of the features is that it can actually emulate a USB keyboard. You can plug it into a computer and have it send Alt-Tab on a pedal press without writing any software on the computer side, and it will work anywhere.

See this tutorial: http://blog.makezine.com/archive/2011/04/the-awesome-button.html
Basically, it uses an "Easy Button" (you'd use the pedal) to enter a pre-set keyboard character or characters (Alt-Tab in your case) through a USB port. It should have everything you need to figure out your project.

The Teensy++ is smaller and cheaper than an Arduino and can be hidden in your pedal box, tidy as can be. A program to do what you desire would take less time than installing the Teensyduino software into the Arduino environment. I think it is the bomb, particularly for keyboard and MIDI stuff (you could make a pedal for "Start Song" or the all important "All Notes Off").
http://pjrc.com/store/teensy.html
http://pjrc.com/teensy/td_keyboard.html

There are several recipes in Arduino Cookbook related to using an Arduino to emulate a mouse and/or keyboard.

Use USB to activate MOSFET/Relay

I am working on a personal project involving sending simple signals from my computer to a circuit via USB. Basically I am using the USB signal as the gate signal for a MOSFET which will in turn activate a relay to turn on/off various AC peripherals. For example if I want to turn on a light bulb for 5 seconds every minute I would be sending a 1 down the first wire for the first 5 seconds of every minute.
This is my problem: I have no idea how to manually send a 0/1 down a specific wire on a USB cable, or even interact with a USB port at all :(
So I guess there are multiple parts to this question, is it possible to interact directly with the bits being sent via a USB port? If so how would I do this? I am familiar with C++ and C#, so I really hope that you can do it in one of those...
Thanks!
edit Hmm so it looks like the USB port actually only has one 5V pin so direct USB interaction wont work. Going to take a look at a parallel adapter and get back on it.

USB is a bad fit for anything that doesn't have a USB interface at the other end of the wire. If you don't want to get into building your own USB device, I'd suggest buying a USB to serial adapter, which gives you two directly-controllable output lines (the flow control lines), or a USB to parallel adapter, which gives you more than 8 lines.
Chris Johnson's answer has a link to instructions for Windows serial port programming. You'll want to look at section 7 -- the SETDTR, CLRDTR, SETRTS, and CLRRTS are your flow control line toggles (for the DTR and RTS lines, respectively).
As far as hardware goes, a "1" (SET) value on a flow control line is +3 to +15 volts on the line, and a "0" is -3 to -15. Actual voltages can vary between devices; measure it to be sure. (EDITED; I got the 1 and 0 mixed up. The control lines use the opposite convention from the data lines.)
Here are Wikipedia pages for voltage characteristics and pinouts.
EDIT: Having done some more research on USB-to-parallel adapters, I don't think they will give the needed level of control. For best results, you'll need a PCI or PCMCIA parallel card, or a parallel port built into the motherboard.
I'm not a Windows programmer, but this library might be useful for controlling the parallel port's lines from Windows.

The easiest thing to do for this application is to use serial port emulation, either with a USB-Serial cable, or with a USB-Serial converter chip (e.g. the FTDI FT232) in your hardware device.
Either way, this allows you to interact with your USB device as you would a serial port (see, e.g. here for how to do this in C++ in Windows)

Much like Chris suggested, you can get a USB slave device from FTDI. $27 at digikey will get you a small board with all the fine wiring already done.
However, for your purposes the bit-banging mode described on page 39 of the datasheet would be much better than the UART mode (UARTs generate pulses at several kilohertz, you want to have the voltage stay at the level you set it to).
Hopefully your MOSFET will turn on with a 3V signal since the FTDI will put out approximately 3.1-3.2V for a high output.
Also, make sure you use the latest drivers from FTDI... a couple years ago they had drivers (WHQL-certified even) that caused frequent BSOD, and I've often found that driver CDs that come with hardware are several years out of date.

I built something very similar to what you are doing (I was running a car window motor from a usb device, used a mossfet H bridge (the HDR1X8 on the diagram) to drive the motor.). You need a USB to I/O device this is what I used (I got a U421, they fit perfectly over the center line of a breadboard, the 401 works well with breadboards too if you don't have a split one.
They give you a dll and you just link in to it with your code. its just as simple as making a call to WriteA and WriteB for writing out to your mosfet device. Be warned logic level lines are not meant to drive current so you will need to hook this up to a transistor if you expect any kind of medium to large current flow. See App1 in the application notes of the menu on the usbmicro site to see the proper way to hook it up.

Use a USB prototype board. It usually comes with a software SDK.

Check out these links from my web site:
1.You can use a usb to serial converter. All you need to know is here
2.You can use programming to access the usb directly but for this one you have to have a driver already installed for you device. Details are here