using bar code scanners as inputs

  • Thread starter Mike Piotrowski
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Thread Starter

Mike Piotrowski

I have an application where I want to establish a gate on a conveyor line. I would like to open the gate only when a barcode scanner has
successfully scanned the barcode of the product on the conveyor, at the gate (ie do not let product go upstream until it has been scanned
into the lot tracability system). I was envisioning using a SSR to receive the scanned signal, driving an input on a small plc. Has anyone ever done something like this? I am having trouble trying to get an actual voltage/current from the scanner....

Terence B. Creevan

If you are trying to get a voltage/current from your scanner's serial port to drive a PLC input I'd have to advise against it. However, I have seen some scanners that offer a contact type signal to indicate a successful scan, which you can use to drive a PLC input, or, you can connect your scanner's serial port to your PLC's serial port. However, just because your scanner has
received a successful scan does not mean your product has been entered into your "lot tractability system" (inventory or tracking data I'm assuming). You might want to consider some type of "acknowledge" coming back from your lot
tractability system to indicate the data was received and processed successfully. You may also consider other signals, exceptions, invalid data, unknown product, manual "hand" re-scan required, etc.

Good luck.

Curt Wuollet

Hi Mike

It sounds like you might investigate getting a signal from your lot traceability system. Most barcode systems do something on a succesful
scan (beep, light an led, etc.) but only the more serious types provide a digital output for this. If you don't mind a little surgery on the
reader, a 50 cent optoisolator could replace the led or parallel the beeper and provide a signal for you. This would eliminate the ssr and in most cases could go directly to the PLC input with isolation to keep everyone happy. If you do have
an output and it's not working, that's another story. It's not at all clear what you mean by "scanned signal". I do this sort of thing a lot and if you provide a little more detail I can probably help.



Zan Von Flue

I don't know which PLC you are using and if a Scada node is possible, however I use a S7 (both 300/400) with TCPIP/H1 connection to a scada.
The scanner is on the HMI which reads the barcode, then inserts the number in the PLC. The Scada reads the number and signals the PLC if the
number(artical) is valid or not. It's also possible to connect the scanner on a rs232 input or maybe profibus. It was just easier to connect
it to the HMI because the scanner input (RS232)was already there.

Grayg Ralphsnyder

Instead of replacing the LED with an opto-isolater, install a photo-sensor compatible with your PLC input to pick up the output of the LED. This gives you the input plus you don't have to mess with the barcode equipment (design, warranty, etc.) and its easy to do.
I am Vladimir.
I have to connect serial port CH0 of SLC 500 (5/03) to bar code reader.
Question is new for me.
Any advice - reader type, program sample, any useful info.
Thanks a lot for your attention.