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Art Allen, KY1K
>The IR receiver has been taken from a trashed VCR. I've tried a few
>discrete designs in the past but never managed to come up with anything
>as effective. Although the power consumption is sort of OK at 1.5mA at 5V
>(the slave battery power), if anyone knows of a circuit as good as a VCR
>receiver at lower power I'd be interested.
For improved sensitivity, go to baseband IR (not 40khz modulated
'carrier'). Crudely collimate the transmitter LED so you get a 5 degree
beamwidth (NOT 90 degrees or more)! You will need IR filtering on the
receiver-go the cheap unexposed film route here. Use a very modest lens to
gather additional photons for the receiver-this is not so much to gather
photons tho....it's primary function will be to minimize the field of view
for the receiver. Maxim has some op amps that draw microamps and the
receiver can be build with an op amp nad a separate photodiode. DO NOT
waste your time with phototransistors or phototransistor based receiver
I am unaware of a vendor that makes a combination PD/op amp combination
receiver that draws low power but the opt 209 from Burr Brown is
ultrasensitive and runs at reduced supply current (400 ua). The opt 301 is
easier to use as it is self shielding and uses slighlty more power-check it
Thanks for the suggestion. I've tried the local Burr-Brown agent, no luck.
manufacturers are represented in New Zealand but finding shelf stock can be
a trial sometimes, sadly. Think I'll have to re-visit a passive IR circuit
if it can be modified. That uses a TLC272 in low current (10uA) low
mode with a lot of gain. The current project is OK with said VCR unit, no
[ More urgent is finding out why my audio system keeps crackling before I go
or it gets a swift kick up the tweeters :-) ]
> out too.
Sharp I.R. modules (RX) are sold by Dick Smiths, 38KHz.
You MUST use an AGC pulse unless the PWM bursts are exceedingly long, as
to the S/W implementation, try to arange TMR0 ISR to be greater than the
total code burst for easy code writing.
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