Do check a 555 - I built one of those years ago while in high school &
was rather impressed with the range you could get (3-4 foot very easily
off a doorknob.)  Put a foil tape piece on the window and turn the
sensitivity up some, and you're set.  (Except for battery life!?  THAT
may be a problem, frankly.  Use a CMOS 555?)

Probably a better answer:  http://www.qprox.com/ has various proximity
sensors, you can take a look at those;  Some pretty fair prices IMO.
Self-calibrating, can act as a reed relay replacement when configured
properly.  Look at the QT110, 30uA or so at 5V.  $2.47 in 1k quantities,
probably $5 in singles?  Just drop it in series with the ISD14000.  That
price is a lot more like it...

  Mark

Mauricio Jancic wrote:
> Hi people,
>         I'm looking for some ideas on how to make a "people detector". The idea is to make a device that plays a pre-recorded voice message (ISD14000 series) each time someone is in front (or near) it.
>         At the first time, I was thinking on a Datalogic infrared sensor (abou U$S 120 + 21% (taxes) here in Argentina). But there were two problems: 1st.  The high price in relation to the rest of the circuit.
>                                                 2nd. As it must be battery powered i make some calc on the total consume and it was too much for me. According to specifications the sensor consumes 25 to 30 mA (the same that the isd when playing) and that get's me to a 2.5 weeks with a 12Ah and 12 v battery.

>
>                                                 3rd. It isn't very nice to put such device on this simple circuit.
>
>         So, wath im looking for is some bright and ease to build ideas on infrared or ultrasound "spectrum".
>         Do you have any??
>
>         Thank in advance, Mauricio.

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