Using computer for Door locks, windows....(attn Aaron)

**wizardPC** · 01-09-2002, 09:37 PM

on Aaron's web site, which is quite old, there are instructions on how to automate your room by interfacing with the parallel port to turn relays to control lights, TV, etc.

I assume very few (none) of you have printers, although some use the parallel port for LCD's. Why not use the parallel port to control your A/C controls, door locks, windows, or even to start the car?

ok, well maybe not to start the car. I'd hate for a story to start out "well, my computer crashed, and then my car did."

So I have a few questions for all of you, but mainly directed at Aaron.
First, why hasn't anybody done this yet? or have they and I just missed it?

Second, on Aaron's web site I get a bit confused. There are instructions to build an ISA interface card. Is this even needed? I ask because the programming section leads me to believe I can just hook up some 5V relays and run them directly.

And he mentions being able to control up to 128 switches using de-multiplexors, but never mentions how to do it. Schematics would be nice.

I am taking VB this semester and I am totally bored already. I have never programmed in VB, but I am fluent in C/C++ so all this talk about the flow control is really boring.

anyway, any help would be greatly appreciated.

**PatO** · 01-09-2002, 10:37 PM

Many of the Matrix Orbital LCD's have General Purpose Outputs (GPO). You can control these outputs via strings sent through the serial port. Just hook 'em up to a relay, and bam! (As Emeril says)

A little pricey, but if you want a character LCD in your ride, it's a simple solution.

mnbujold · 01-10-2002, 12:53 AM

Heh. This talk reminds me of a running joke in my car. I was too lazy to hook up a power swich, so the PC is hooked directly to the acc. line. When the car is on, so is the PC.

So of course, when the PC crashes, I have to 'reboot' the car as it were.

**Aaron Cake** · 01-10-2002, 09:25 AM

Originally posted by wizardPC:
on Aaron's web site, which is quite old,

Hey! I'm working on an update right now. It takes quite a lot of effort to update a site that size...

I assume very few (none) of you have printers, although some use the parallel port for LCD's. Why not use the parallel port to control your A/C controls, door locks, windows, or even to start the car?

Don't really know why not. I know there have been discussions in the past, but they usuallly end with "PCs are too unstable". And I can see the annoyance in having to wait for a PC to boot before you can start the car.

ok, well maybe not to start the car. I'd hate for a story to start out "well, my computer crashed, and then my car did."

If Microsoft built cars...

Second, on Aaron's web site I get a bit confused. There are instructions to build an ISA interface card. Is this even needed? I ask because the programming section leads me to believe I can just hook up some 5V relays and run them directly.

If you are just using the parallel port, then you don't need the ISA card(s). In theory, you could use small 5V relays directly on the parallel port, but the interface provides a much needed safety buffer.

And he mentions being able to control up to 128 switches using de-multiplexors, but never mentions how to do it. Schematics would be nice.

Check the datasheets for the 74LS154 and 74LS138 demultiplexors at http://www.national.com. They include sample schematics. Once you see how it's done, you'll realise how simple it is. But using a demultiplexor makes programming a little more complex as you now require a loop to quickly scan through the outputs...This will make sense when you see the schematic.

**SuperMatty** · 01-10-2002, 01:19 PM

I'm sorry...this may be a trivial question, but don't you folks mean to be saying to hook the parallel port up to a transistor, not a relay? I can see where you might use a relay for when you want to have something activated BEFORE you send the high signal to the parallel port (i.e. the normally closed wire) but for what you have all been describing it seems a simple transistor would fill the role. Am I missing something?

**wizardPC** · 01-10-2002, 06:10 PM

the problem with transistors is they would fry if you sent more than 5v through them (like 12v for anything in your car)

and relays are safer because they can switch high currents without frying.

**Rob** · 01-10-2002, 06:19 PM

Having connected most things to my parallel port over the years (I know I must get out more) here's my 2p worth.

DON'T connect relay directly to the port! The average port can only put out a few mA, a relay require way to much current, and bang there goes your MB. Trust me, even LEDs can kill a MB.

Use transistor amplifiers, or if your not that good with electronics use a Buffer IC like the 2803.

IF your not sure experiment with a parallel port card, there a lot cheaper to replace than MBs!

It's pretty simple to connect relays to a ISA bus via a home made card, it takes about 5 IC, I've got a design around here some where if you want one.

It's pretty simple to build a multiplexer which can be controlled by the status pins, see Discolitez for a circuit.

Also I've got a bit on my site dealing with this whole topic, including software. Note I havn't touched this since I was at Uni and some of it's out of date.

I hope this helps, rather than confuses things.

Rob

**wizardPC** · 01-10-2002, 06:37 PM

can you give me a direct link to that stuff? I dont understand how to navigate your website

**Rob** · 01-10-2002, 06:47 PM

Don't worry your not the first person to be confussed with my site

Trythis page as a starter.

Most of it relates to controling disco light but you can use the hardware and software for any thing.

Email me if you've got any further questions. Unless they relate to Linux.

Rob