serial line driver and receiver

This circuit owes its existence to the need for data communication over relatively long distances (up to 100 metres), inexpensively, reliably, and suitable for speeds up to 2400 bauds. At the distances considered, the main expense is normally the cable, so here a readily available 60 Q coaxial cable is used. Because of its relative immunity to noise, current drive is employed. In the line driver — figure 1 — transis- tor T1, diode D4, and resistors R3 and R4 form a current source that can be fed direct from a non-regulated supply of 8...10 V. The transistor should be mounted on a heat sink. The current level of 40 mA ensures an adequate 1 40 mA 100 16 V serial line driver and receiver (TTL) 0 02 1N4007 BC 547B 01 12 1N4148 2V7 400 mw BC 516 t 1N4007 85443.1 8 .10 V 140 ,,A) 7-21 input signal to the line receiver. Tran- sistor T2 is a current switch that short-circuits the current source and the cable to earth of the input to the driver is logic high: only when that input is ...