21 Sep
2013
21 Sep
'13
10:40 p.m.
I'm looking at the converter schematic but it is onpage 37?If it is a 8L, I figure 20
mA.It is -30volts to +5V or 35V.R1 and R2 are 1K and 750 or 1750 ohms.35/1750 = .02 amps
or 20mA. Point N is pulled to -10v when there is 20mAflowing.One could clamp point P to
-10V with a 10 voltzener to ground. That would still get the 20mAwhen the contacts were
close but limit the voltageacross the contacts ( RS232 converter ) to 15Vinstead of 35V.A
half watt zener would work here as it is only0.2Watts to deal with.I hope this makes
sense.Dwight