[top-posting and no-trimming damage repaired manually]
+-----------+-------- +5V
| |
4.7K Ohm Collector
| .
D33D1 --- 220ohm ------+-------- Base Q1, PNP Silicon
.
Emitter ----- 47 Ohm ---+--- RS-232 OUT
|
3.3 K Ohm
|
-12V (Regulated)
Sure
you don't have collector and emitter switched on that diagram?
Or, maybe its
NPN. I'd have to look at the card to be sure.
If so, then I'm astonished it works at all. If it's NPN and the pinout
markings are correct, then the output voltage swing should be
approximately the TTL range, never going very negative relative to
(circuit) ground. Also, the 4.7K resistor is in a weird place in that
case, whereas it makes perfect sense for a PNP with C and E switched.
Also,
you're getting close to the RS-232 undefined voltage area
there, [...]
+5V is used with RS-232 all the time.
Yeah, and the resulting serial ports tend to be unreliable, especially
when getting close to the cable length limits and/or with relatively
low-impedance input circuitry on the driven side.
I built this thing in 1985, on a tight budget, long
before there were
inexpensive DC-DC converters. ;)
And no +12 easily available? Well, if it does what you want then it's
suitable for you; I'm just a little concerned about anyone else using
it for purposes different enough from your use case for the respects in
which it's borderline to matter.
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