infrared beacon for pet door

I have a cat door and now I have way more cats than I used to. I want
to block all cats except for my cat, so I figure I will make a little
lock on the cat door that only unlocks when my cat walks up to it. I
will fit my cat with a collar that has infrared LED's which emit a
short pulse a few times a second. There will be a infrared receiver on
the door which looks straight down at the cat door, and when it sees
this short pulse, will unlock the door.

I know this can be done with RFID, radio, magnets, etc... fill in the
blank. I want to do it with infrared. I haven't played with any opto
circuits for a long time and I miss them.

I know there are already devices for sale which do this.

SO.

I am thinking 1 to 3 button cell 1.5V batteries to power the collar.
These are 150mAh each. I want the batteries to last at least 3 months.
The receiver on the door will be powered by wall power so there is no
problem there.

I dont want to make a transponder collar, I want it to simply emit a
short infrared pulse at a fixed interval.

So basically its a game of reducing the infrared pulse to meet the
battery life requirements, but still be able to detect said pulse.

The cat should not have to wait more than half a second after walking
up to the door before it unlocks.

Lets say somehow the pulse is 10uS long, twice a second, and the total
current used by 3 led's is 30mA.

So assuming a square wave driving the LED's, its 15mA average current.
And for 10 us, its 150nA per pulse, and at two pulses per second its
300nA.

Per hour its 300nA x 3600 = 1.08mA.

Per day its 1.08mA x 24 = 25.92mA

So a single 150mAh battery would last about 6 days.

Thats not gunna do it!

What can I do?

Use sub microsecond pulses? Can those be detected at 6 feet?

Remember, no transponder! (not yet anyway)


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