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Serial RS232 Booster Up to 100m (BC516)

2017-07-22 04:02  
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This circuit can run 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 thecable, so here a readily available 60 ohm coaxialcableis used. Because of its relative immunity to noise,currentdrive is employed. In the line driver – figure 1 – transistor TI, diode D4, and resistors R3 and R4 form acurrentsource that can be fed direct from a non-regulated supply of 8. . .I0 V. The transistor should be mounted on a heat sink.

1328771384549 Serial RS232 Booster Up to 100m

1328771426891 Serial RS232 Booster Up to 100m

Thecurrentlevel of 40 mA ensures an adequateinputsignal to the linereceiver. Transistor T2 is acurrentswitch that short-circuits thecurrentsource and thecableto earth of theinputto the driver is logic high: only when thatinputis logic low, is thecurrentof 40 mA fed into thecable. Diodes D2 and D3 protect the driver against noise emanating from thecable, while capacitor CI decouples the supply line. The linereceiveris based on a type LM 311 comparator. Matching of theinput
is effected by a wire link at a relevant tap of resistive divider
R5-R6- Rd Rs (in our case: 60 R). Resistors R9 and Rlo, and diode D5
protect the LM 311 against noise emanating from thecable. The sensitivity of thereceiver
is set with Pi Resistor R14 provides some hysteresis. Pull-up resistor
RIS ensures that IC, provides at its pin 7 a TTL output signal that is
in phase with theinputsignal to the line driver. The
circuit is best calibrated with the aid of an oscilloscope once it has
been installed in its final position. The level ofinputto thereceiver
is then compared with the voltage at the wiper of Pi The setting of P1
is optimum when the voltage at its wiper (wave form A in figure 3) is
exactly opposing theinputvoltage (wave form B in figure 3)