USB interface

[TheChief]

I'm wondering is it as straight forward as I imagine or is there some gotcha that I may be overlooking.
What I want to do is interface a PICAXE with a USB device. I can successfully connect to the device via a terminal and issue AT commands from my computer.
Is it simply a matter of butchering one end of a USB cable and using pins 2 and 3 for data to the PICAXE and lay on a 5V supply to the device on pins 1 and 4 of the USB cable?

 

[Buzby]

No, that won't work. Pins 2+3 carry USB data, not serial data like a comm port.

But I can't see how you are communicating with a USB device by using terminal.

Are you sure it's USB ?

More details please !

 

[lbenson]

>But I can't see how you are communicating with a USB device by using terminal.

Many older "dumb" cell phones have usb connections with which you can communicate using a cable and a terminal on a PC. Some have actual serial, but usually require a special connection (not usb). GPS modules may also converse using usb/serial.

But Buzby is right--the ability of your device to communicate via serial to your terminal is because of usb hardware and firmware in the device and in the PC, and picaxe does not natively or easily support that.

 

[TheChief]

What I have done is connected the device to my computer via USB cable and connected to it using Minicom terminal emulator program.
The device is actually a GSM modem that will accept AT commands.

 

[TheChief]

So looking at this I would either need a USB to serial such as an FTDI chip or I would need to break into the existing circuitry on the device and bypass the USB stuff assuming that it actually does use serial on the actual main chip for communication.

The device in question is below and I believe it uses a Wavecom GSM module.

http://item.mobileweb.ebay.ie/viewitem?itemId=251069726659&index=4&nav=SEARCH&nid=82685367841

 

[hippy]

I have no idea how this unit works but it may be there is no serial per se other than it providing a virtual serial port under the Windows OS. In which case there would be no way to bypass the USB within the unit, and no easy way to communicate with it from a PICAXE - A USB-to-Serial interface won't do the job, you need a serial to USB Host interface and I don't know of such an item.

It may be the unit is 'real serial' and simply includes an in-built USB-to-serial interface to make it look like a USB unit. Perhaps open it up and take a look at what's on the PCB; these modems are usually very easy to take apart. Post photo's and people here can make guesses.

What does Device Manager say about the driver used to create the unit's virtual serial port ?

 

[lbenson]

You wouldn't need a usb to serial chip, but a serial to usb.

Do you need to use a picaxe as opposed to something like the pogoplug: http://www.jr.com/pogoplug/pe/PGG_POGOP21/

This $20US device will apparently run archlinux. Since your gsm module has "2303" in its name, I would guess it is a pl2303 serial device, so drivers would be available.

 

[TheChief]

I just wanted to get it working with a PICAXE. I have a Raspberry Pi and as you pointed out from the model number it probably contains the Prolific USB chip, there is defiantly kernel support available for this chip as I recall compiling support for this chip on a USB to serial cable I have.

 

[TheChief]

Ya I think I'll have to abandon this project. The board does have a Wavecom main GSM module and the PL-2302HX USB module. That smt stuff is a bit small to start tinkering around with.