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sending 12V signal from a Barcode Scanner to a PLC?



Jan 1, 1970
Anyone has any advise on how to send 12V signal from a Barcode Scanner to a PLC?



Jan 1, 1970
LongBow said:
Anyone has any advise on how to send 12V signal from a Barcode Scanner to a PLC?


Hi, LongBow. Choose a barcode scanner with RS-232 output, and a PLC
(programmable Logic Controller, an industrial computer with built-in
I/O generally used to run machines) with RS-232.

Most of your difficulty will be in programming the PLC to deal with the
character string and the PLC serial buffers. Sorry, no recommendations
on which barcode scanner to buy. I decided to use a PC in place of a
PLC for that machine the time I tried it. The tradeoffs led me to
decide the additional hardware hassles of a PC would be compensated by
the much easier software route (including drivers from the barcode
manufacturer). Try to pick the easiest way to reliably solve the

Also, if you're doing it this way, try not to get a free-running
barcode scanner. The PLC serial buffer can be impossible to deal with
when it overruns, and resetting things can take forever. You don't
want this hassle, and you never get the flexibility in a PLC you have
with a PC serial port. Get one that sends data on trigger (either a
button on the scanner, or on a signal from the PLC)as an option. This
is another issue where having a PC instead of a PLC solves a lot of
problems, especially if you've ever programmed serial comm.

Another thing you might want to try is to call the apps engineers at
the manufacturer of the PLC you like. They're usually very helpful,
and frequently will provide sample software for their preferred barcode

Questions of this type usually receive a better reception on
sci.engr.control. Try posting there for a lot more advice.

Good luck on your project


Jan 1, 1970
LongBow said:
Anyone has any advise on how to send 12V signal from a Barcode Scanner to a PLC?

not sure in what form you need the signal?

if you get a RS-232 type, the output should be around
12 volts. of course you need to decode RS-232 protocol.
some PLC's do have a RS-232 input that you can use in the
latter logic.

if all your looking for is to create a trigger from the
output of a scanner to signal the PLC that it's scanning ?
i guess you could use a simple op-amp to bump the voltage
i don't have a Ascii utility to draw it here for you but i
will explain.

using a TL082 op-amp or similar with a + & - 12 volt supply

the + input is the input to use from a on condition signal
from the scanner ( even if its pulsed), the - input will have a
Resister to ground(common)R1, also the - input will have a resistor
to the output of the Op-amp R2.
now, you need to calculate the 2 resistors to get your proper gain
that you need.
Gain = (R1 + R2) / R1

or the reverse to come up with some Resistors.
lets assume the logic from the scanner is 5 Volts.
Gain would need to be 12/5 = 2.4

now to come up with total T network. in this case i will
use 10K to start with.( because i like 10k :));
R1 = 10,000/2.4 = 4166 ohms.
R2 = 10,000-4166 = 5834 ohms.

of course those are strange size resistors.
you would have to round them to the nearest that you
can find.
the output of the op-amp can signal a PLC input.
your latter logic would have to account for pulses if that
is what your monitoring?.
just an assumption on my part! :))