0

I'm trying to communicate with a serial barcode scanner. This is how i've linked it to my computer (the circles represent the color of the wires already soldered in the serial plug) :

http://img441.imageshack.us/img441/6126/0079.png

When I scan a barcode (a special one telling the scanner to send an ASCII debug) or just a normal random barcode, all I can see in my serial terminal are accentuated letters and I don't understand why I can't see the barcode. I think the baud rate is fine, and I don't know if it's encoded or something...

Could you help me figure it out ? This is what I get :

ÍøÌÔÃøÃÇøÇËøËÊøÊÎøÏËøÊÎøÎÏøÏÓøÓÑøÑÖøÖøÔÐøÐ×ø×ÔøÔ
mimipc
  • 161
  • 1
  • 1
  • 5
  • 3
    Have you checked the baudrate and other settings? – Gustavo Litovsky Mar 11 '13 at 19:39
  • Yes I have, there's a configuration barcode to set the baudrate at 9600, and I've tried all other common baudrates. – mimipc Mar 11 '13 at 19:55
  • 1
    Wow. I just noticed that you connected an FTDI to RS232. Those are not compatible. RS232 uses much higher voltage levels than UART, unless your FTDI board includes level translation. Otherwise, you will likely damage the FTDI device due to the higher voltages. – Gustavo Litovsky Mar 11 '13 at 19:56
  • Also your wiring seems entirely wrong for a 9-pin RS232 connector. If the device is not a standard RS232 peripheral but some unique scheme, please link the manual or wherever you obtained this unusual pinout. – Chris Stratton Mar 11 '13 at 20:08
  • Yes, I know, but that's how it's made inside it... – mimipc Mar 11 '13 at 20:19
  • @mimipc, then it quite likely is not an RS232 device. What made you think you should be supplying 5v to it anyway? – Chris Stratton Mar 11 '13 at 20:27

1 Answers1

4

The "FTDI friend" is the wrong tool for the job. What you want is a cheaper, off the shelf USB to RS232 converter from a generic computer or office supply store.

As Gustavo points out, the signaling voltage of the FTDI friend is incorrect - about 3.3v unipolar instead of the higher, bipolar RS232 levels used by just about anything of recent vintage that has a 9-pin serial cable.

However, that's not the only issue. The "sense" of the logic is also customarily inverted between logic level and RS232-level serial signaling. So even if there were not a potential damage issue due to the voltage incompatibility, the upside-down data would not be interpretable by a typical receiver.

It might at first seem ironic that a USB-serial chip packed with a a converter to RS232 levels and a 9-pin connector is cheaper than a module with just a chip and the signals broken out at logic level to wires, but not really, when you consider the size of the market for the two products.

Chris Stratton
  • 33,282
  • 3
  • 43
  • 89