RS232 Control of Switches

[Jim Murphy]

Does anybody know of a simple circuit that will allow control of at
least 8 switches from a PC serial port (9 pin RS232)? I can access
the serial port by code, so the structure of the enabling signal isn't
important--I can make it whatever it needs to be. What I envision is
maybe a simple microprocessor reading a byte and flipping switches
based on bit analysis, which would remain closed until 1) reset is
thrown or 2) another byte is received which would automatically
trigger a reset. Even that is a bit more complicated that I want,
which is basically just a switch controller connected to RS232.

Thanks for any help.

--Jim Murphy

[Michael A. Covington]

Try this:
http://www.elabinc.com/ede300.htm

It's a pre-programmed microprocessor.

"Jim Murphy" <j...@usa.net> wrote in message
news:53850cdc.03050...@posting.google.com...

[Ian Stirling]

The parallel port may be even easier.
All you need is a relay driver chip.

--
http://inquisitor.i.am/ | mailto:inqui...@i.am | Ian Stirling.
---------------------------+-------------------------+--------------------------
"The theory of everything falls out trivially." -- Etherman, sci.physics kook.

[Tom Woodrow]

check out the $59 DIO module from www.weedtech.com

[petrus bitbyter]

"Jim Murphy" <j...@usa.net> schreef in bericht
news:53850cdc.03050...@posting.google.com...

Jim,

The current (May) issue of Elektuur (the Dutch Elektor) has an article that
describes a circuit that can switch up to six relais that switch mains. It
uses a PCs COM-port and an I2C chip. I din not check it out but I think it
can be expanded to eight switches without much difficulties. Anyway you have
a good example of the possibilities.

pieter

[dmi...@spamblock.demon.co.uk]

IIRC there are two or three handshake output pins available, convert to
0 -> 5V (series resistor, zenner diode sort of thing), then tie one line
to the input of a Serial in - Parallel out shift register and the other
line to its clock.....

The relays actually used for switching are fairly slow so the hash as you
clock the new control word into the shifter should not cause anything to
happen.

2 chips (shifter and relay driver), 2 zenners, 2 resistors & 8 relays by
my count (plus some decoupling & catch diodes if needed).

I think a micro is overkill for this application as it does not reduce the
chip count and will be more expensive then a simple 8 bit shifter.

Regards, Dan.
--
** The email address *IS* valid, do NOT remove the spamblock
And on the evening of the first day the lord said...........
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[simon]

Check out the BL232 IC at
http://www.i2cchip.com

You can use it with any I2C chips that do your job (eg PCF8574)
It is also able to be used directly as an I/O chip if you don't use the I2C.

Simon

"petrus bitbyter" <p.k...@hccnet.nl> wrote in message news:<80Psa.296317$ZG5.26...@amsnews02.chello.com>...

[John Smith]

<dmi...@spamblock.demon.co.uk> wrote in message
news:g0139b...@spamblock.demon.co.uk...

> Jim Murphy <j...@usa.net> wrote:
> > Does anybody know of a simple circuit that will allow control of at
> > least 8 switches from a PC serial port (9 pin RS232)? I can access
> > the serial port by code, so the structure of the enabling signal isn't
> > important--I can make it whatever it needs to be. What I envision is
> > maybe a simple microprocessor reading a byte and flipping switches
> > based on bit analysis, which would remain closed until 1) reset is
> > thrown or 2) another byte is received which would automatically
> > trigger a reset. Even that is a bit more complicated that I want,
> > which is basically just a switch controller connected to RS232.
>
> IIRC there are two or three handshake output pins available, convert to
> 0 -> 5V (series resistor, zenner diode sort of thing), then tie one line
> to the input of a Serial in - Parallel out shift register and the other
> line to its clock.....
>
> The relays actually used for switching are fairly slow so the hash as you
> clock the new control word into the shifter should not cause anything to
> happen.
>
> 2 chips (shifter and relay driver), 2 zenners, 2 resistors & 8 relays by
> my count (plus some decoupling & catch diodes if needed).

Shift register and relay driver in one: STPIC6C595 in SOIC by ST or
TPIC6C595 in either SOIC or DIP by TI.

Good luck.
John