How to control external device through usb port

i am doing an automatic numberplate recognition system for acces control, i want to interface a motor controlled barrier, which will be triggered by a command to the usb port of the computer if a particular plate is recognised in a database and is allowed in. what commands can i use to trigger the external device? #clueless!

Answer 1

[Image Analyst]

Model of what ? What is the "external device" ? Is it a camera? A bar code reader? And what is the "(toy) boom" you're going to attach to it? Do you mean boom like a loud sound (like your toy explodes) or a boom like a movable horizontal arm used for hanging things? Do you want a camera (the device) to read the license plate number off a toy car, and then look it up in a database, and if the car is authorized, to lift a a crossing guard arm (the boom) to let the car proceed to drive forward? Just a guess since I can't figure out what you're trying to say.

[Nakk Mungofa]

oh sorry for that, the question IS indeed not clear, just realised! i have done the image processing of capturing a number plate and doing OCR... now i need to actuate a boom (horizontal crossing guard arm) to let the car proceed forward... can i do this with matlab? i.e control the boom(horizontal crossing guard arm)

[Image Analyst]

Yes you can. If your arm-lifting device has a DLL for it, then you can call loadlibrary() and call functions in that DLL. I talk to Measurement Computing Devices, which are attached to a USB port, with their DLL. For example see the attache code where I read a switch closure attached to the MCC device.

P.S. I know it looks scary at first glance but take a deep breath and just take it a line at a time. It's very well commented so you should be able to handle it.

[Nakk Mungofa]

thanks a lot hey! lets see hw i do with this

[Nakk Mungofa]

im having a hard time with the DLL and seems your code controls in a different way to mine so question... would RS232 be any easier???

[Image Analyst]

Nakk, obviously unless you have the same device I have, the code won't work for you. Your device is almost certainly different. You'll have a different DLL. My code is just an example of how it is done. Obviously you'll have to make modifications for your device.

An RS232 is probably not easier. In fact since computers don't come with those kinds of ports anymore you'll have to get an USB to RS232 converter and install some software, which can be done (and I have done it), but why bother since you have a USB device?

[Nakk Mungofa]

thanx for the support hey! i resorted to using USB to RS232... and i have been able to run a motor by sending a string through the serial port to a very small PIC external circuit which is able to run a motor... i will still look into the DLL method though for interests sake!