Paul B. Webster VK2BZC says
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From: david@comms.ee.man.ac.uk (David Tait) Subject: Re: Power from RS-232 Date: 30 Apr 1996 11:18:41 GMT 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
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file: /Techref/io/serial/parasitic.htm, 4KB, , updated: 2013/7/22 11:57, local time: 2024/8/14 22:44,
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