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PICList Thread
'PIC 'n IR'
1999\10\08@003404 by John De Villiers

Hi Folks,

I want to build a pic based IR transmitter / receiver for a Home security

Basically i want as many "buttons" as possible on the transmitter and a
receiver capable of decoding al those into relay actions for switching on
electic gates and garages etc.

Any ideas on where i can start?


1999\10\08@015501 by Richard Martin

picon face
A good place to start if, it fits your design scheme, is to use a
'standard' universal TV remote control transmitter, <$US10
hereabouts, and just use the PIC to Rx and decode. You can have
several Tx devices and they are easily replaceable when lost or when
eaten by the dog (or would it be a lion in .ZA?). Place Rx (IR
photodevices) about the house, OR-ed together, so you can
turn on the lawn sprinklers from the bathroom, etc..

Most of the encodings used in U.S. and Europe are on the Web
but it's pretty easy to 'milk' the codes of a variant Tx widget.
You get as many numeric 'channels' as you choose and can, e.g.
use the special "Record" key to turn everything on at once.
Completely impressing the neighbors.


John De Villiers wrote:

{Quote hidden}

1999\10\08@040004 by Mark Willis

One added suggestion here;  Set the remote so it doesn't resemble,
code-wise, any current remote in your house.  You don't want

I have 3 VCR's (legacy of having a poor ex-Girlfriend without a VCR;
long story.)  Apparently, there are pretty much just 3 VCR IR code
styles, these 3 don't interact in any way (which is a GOOD thing!)  Took
some looking to find these 3 (Sony, Magnavox, Symphonic) - I'm sure
there are other combinations.  I didn't have Web access years ago when I
got these (It's been a while!)

You don't want to hit the button for "Play" on your VCR, and set off the
house-wide Panic Alarm or something on that order, for example.  Using
the codes for a brand of VCR or TV that you don't have and don't plan to
have, and that do not interact with your current electronics, should
work great.

(Ex-GF's remotes for the VCR would turn the TV on when you turned the
VCR on or off - so you could turn the VCR on, turning the TV on;  Turn
the TV off, then turn the VCR of, turning the TV back on, if you weren't
thinking.  That unintended interaction was a pain if I wasn't awake


Richard Martin wrote:
{Quote hidden}

1999\10\08@100229 by Steve Kelley

picon face
John . . . .
You might want to begin , by first deciding which  * Infrared * wavelength would
suit your purpose or exsisting hardware.  You should optimize the xmit/rec by
matching both parts ( whether 870 nm or 950 nm ).   Personally , I prefer the 950 nm
parts , because they are further away from * ambient * wavelengths.

You can develop a xmit. routine easily , by modulating the LED  , with a PIC's PWM ,
that is being controlled by a burst data stream.  The rec. routine can implement a
sampling window , that test the width of the incoming data.  When Ired is first received
then start the timer , when the first interruption in the Ired is detected , stop the timer,
test it's count and see if it fits within the minimum / maximum limits you've established.

Even if you use an Ired * Photomodule* to de-modulate the incoming signal , it is very
important that the receive routine have the ability to detect the shortest pulse possible.
This could be as short as 1 msec and would indicate , to your routine , that what the Ired just
received was either a partial bit or the link is out-of-range.   Don't confuse the shortest
possible pulse width  , with the shortest pulse width of your data protocol.  You may have
a   data pulse that is anywhere from  1 to 30 msec.  , but as you loose reception at the
Ired * Photomodule * this data pulse will begin to chop-up into wildly variable slices of
the modulation frequency.    As a rule of thumb . . . . test the data from the Ired
*Photomodule * as often as possible , so that you can detect and toss-out anything below
1 msec.

Regards . . . .

{Original Message removed}

1999\10\08@133301 by John De Villiers

> several Tx devices and they are easily replaceable when lost or when
> eaten by the dog (or would it be a lion in .ZA?). Place Rx (IR

Dunno about the lions, but some of the cats here can make one look twice.

I was thinking about using some or other code hopping encoder to kinda
smooth things out so that no-one else can steal my codes. Any ideas what a
keeloq 64bit encoder costs??

Also, right now im not interested in masses of functions. Basically 4
Garage door, gate door, Home alarm, security lights ).

Now, when i place IR detectors all over the house and garage what do i have
to look out for when it comes to cable lenghts??  Some of these runs could
end up being quite far. ( beroom to other side of the house, down the wall,
across the lawn, up the garage wall and into the roof, about 30-40 meters )


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