A simple terminal program on a PC can have a lot of uses. The hang-up is that most of those uses involve communicating with a device running on 5 volts. I’ve done several schemes over the years but this one is my favorites.
So I built it into a stand-alone box. This design steals the +12 and -12 power from the computer’s serial port. It puts out a very clean rs-232 level signal back to the computer. The output of this device is open-collector with no pull-up to +5. The pull-up is the job of the other device on the other end since it has the 5 volts available.
The switch is used to join the TTL side send and receive circuits for ‘network’ style communication. In the network position, it also engages the ‘anti-crosstalk’ system so that data sent out from the computer will not come back in. This eliminates the software overhead of discarding the reflected data.
Copyright 2006 Luhan Monat