Daniel P. Siu (dps@west.net) wrote:
: I need to derive some power (fairly low, a few mA at 5V) from a RS-232
: serial connection. I remember there are ways to do this (in fact,
: some techniques are used in serial mice). Any help is appreciated.
Here's a circuit I have used (it doesn't guzzle as much current as
a 78L05 which is obviously a much simpler solution):
+----> DSR
2 X 1N4148 |
+-------------+----< DTR
+-----------------+-------------+ | +------+----< RTS
| |C | _|_ _|_ |
| _____ |/ | \ / \ / +----> CTS
+---[_____]--+--| BC550 | --- --- |
| 10k | |\ | | | +----> DCD
| | |E +-----+------+-----------> V++
+__|__ | +----+---------------------+-----------> VDD
_____ +-----+ | _____ | +5V
220u | | | +---[_____]---+ |
| | C| 22k | +__|__
| __|__ \| BC547 | _____
/// _____ |---------------------+ 47u |
100n | /| | |
| E| _____ | |
| _|_ +---[_____]---+ ///
/// \ /^ | 18k
--- |
LO-I RED LED | |
| |
/// ///
Strapping DTR/DSR and CTS/RTS/DCD is just to implement a "null-modem"
connection, the power comes from DTR and RTS. On a typical PC about
5mA can be drawn from the regulator.
David
--
david.tait@man.ac.uk
Date: 30 Apr 1996 11:18:41 GMT
Original Subject: Re: Power from RS-232