RS 232 line indicator

7-30 elektor july/august 1 980 There are now a large number of peripheral devices such as VDUs, TTYs, printers etc. available to the amateur to add to his/her personal computer system. When things fail to operate correctly one of the first checks to be carried out is to make sure that the correct voltage levels are present on the RS232 line inter- connections. A s m any personal computer operators will testify, this is not a particularly easy task when the only test instrument available is a multimeter. Inserting probes into live sockets while looking up the relevant literature for correct connection and simultaneously pressing buttons can be very frustrating — especially when power supply lines are shorted out accidentally! It would be desirable, therefore, to have a device that will check whether or not the signals are present and at the correct levels. The 5V 5V R8 101, 14 6V 15 A0 IC3a D1 R12 T1 5V accompanying circuit is just such a device and can be built into the computer...