RS232 analyser - enables true 'on line' testing

july/august 1984 enables true "on line" testing To be able to use a computer prop- erly, you need a number of relevant peripheral units. These units are often connected to the computer via a serial interface V24 or RS 232. If anything goes wrong, or is suspec- ted of having gone wrong, the ana- lyser described here may prove to be very useful. It is simply connected in series with the relevant line. The ad- ditional load on the line is so small that true "on line" testing is possible. The circuit consists of two transistor drivers for two LEDs: red/red or red/green. With positive levels, in the range of about 4.5 . . . 5.5 V, T1 conducts and D1 lights. With negative levels, of the order of —5.5 . . . —7.0 V, T2 conducts and D2 lights. If R4 is reduced to about 15 k, the circuit becomes active at about —3.5 . . . —5.0 V. It should be noted here that in the RS232 negative levels correspond to logic 1, and positive levels to logic 0! The printed-circuit board can house four o...