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Optoisolator for RS232 interface

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I am interfacing a DVR (PC based, DB9 RS232 interface) with ATM serial printers and POS serial printers. We currently use a simple Y cable with the Tx and Rx spliced into which sends ASCII data from the ATM or POS system into the DVR's serial port and then into the video database, as well as printing on the serial receipt printer.

However, I need to build some sort of box which isolates the PC from the ATM/POS serial output and from the printer. I was thinking of using an optoisolator. I therefore need to find a circuit diagram of an optoisolator or similar circuit for RS232 splitter box.

Any ideas anyone?

Appreciate any help,

You can use any RS232 IC, like th MAX232, its has a TX and RX while both RS232 Levels adn TTL levels, if you're signal is not TTL you can use another interfacing circuit ot IC for the TTL input and output to level down the signal or level them up.


New Member
Here is an RS232 circuit that I have been using with common PC817 optoisolators. The +12V and -12V supply is taken from the DTR and RTS lines (pins 4 & 7 respectively). Therefore, in order for this circuit to work properly, the PC software, when opening the COM port, should activate the RTS and deactivate the DTR line or viceversa.


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