The project we have chosen as our example is an RS232 to RS485 converter. This is a often needed device which can demonstrate a lot of principles of circuit design, and hopefully the finished project will be useful to some people, just as it stands. Without meaning to confuse the issue, we also have available a second, more up-to-date 232-to-485 converter. This project demonstrates how we produce an electronic project using one particular PCB CAD package. Our business is about producing finished custom electronics, and the PCB design process is an important part of that. This page might be of interest to new designers wanting to learn principles, or to potential clients wanting to understand our processes more thoroughly.
Click here to download the full size of the above Circuit.
DE9 RS232 connector compatible with PC
TxD and RxD translated from RS232 to RS485
Direction of transmission controlled by PC RTS line
Handshake loop the PC connection so it works with all software
RS485 signals output on 6 way modular jack
Indicator LED(s) to show communications traffic
Power supplied by external unregulated 9v plugpack
... and a few extra features, not essential, but desirable
RS485 Termination resistor, jumper selectable
Pullup/Pulldown resistors on RS485 to establish line-idle condition
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