PC Serial IR Interface

[Patrick Lidstone <patrick-lidstone@xxxxxxx>]

>
>
>While everyone is discussing the topic of Home Automation, I have a few
>questions about Infra Red devices that I am hoping someone can answer.
>
>I am about to start working on a University project involving the
design and
>production of a serial device that can receive and transmit IR signals
allowing
>the ability to control anything with a remote control.
>
>Due to the fact that I have very little in the way of electronics
experience I
>have asked a friend to build such a device.  While this is being
completed I
>have been using a ONE-FOR-ALL 6 and 8 with a serial interface purchased
from
>America to allow basic control of pre-programmed devices via a Visual
Basic 5
>interface and via Voice Control using Dragon Dictate.  At present this
system is
>working very well but is a little restricted.

It's probably worth noting that All-4-One appear to have recently revised
the design of their remotes, and current UK versions no longer have the
required 3 pin interface connector for use with the serial cable. Due to
the way the remotes are packaged (blister packs with card backs) most shops
are reluctant to let you inspect the remote before purchase.

>I have read countless papers on IR data protocol, I managed to
understand
about
>30% of them, but cannot workout how to convert the required signals
into
>something I can send via a serial port.
>
>Has anyone had any experience of using such a device (Systems such as
the
Red
>Rat and other IR->PC links).  Or is thinking of doing a similar
thing.

I took a very naive approach. I used a digital input port (a pin on the
parallel printer port would do - although I used a dedicated interface
board), wired this to the All-4-One IR LED, and ran a trivial program to
capture the digital data from the transmitter on each key press.

Now wire an IR LED to a digital output port pin (again, the printer port
would do) - I used no series current limiting resistor to get maximum
output, BTW - and play back the captured signal.

You need a fairly fast PC to get away with this approach (P100 works well,
486DX25 struggles a bit), and the record and playback programs needs to be
symmetrical timing wise - but much to my surprise, I've found it works
really rather well, despite the lack of a properly modulated carrier
frequency. Range is 3-4 feet, but this could be increased by adding more IR
LEDs with the appropriate driver circuitry.


>I would also like to include the ability to switch the video on or
activate
>pre-programmed macros via a touch tone phone from anywhere such as from
work
>using a Data/Voice/Fax modem.

This is exactly what I've done - I can phone my video and follow the voice
prompts to select a channel on the cable box and start recording. Rather
neat! There are a couple of flaws with the scheme - IR control offers no
feedback, so you can't be absolutely sure the command has been followed
correctly - and, of course, you have to have a video tape in the machine
ready for use.

Works well, on the whole, though.

Patrick

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