Re: Proximity sensor

On Apr 27, 10:18 am, Jan Panteltje <PNaonStpealm...@xxxxxxxxx> wrote:
On a sunny day (Sun, 27 Apr 2008 09:46:21 -0700 (PDT)) it happened linnix
<m...@xxxxxxxxxxxxxxxxxx> wrote in
<085ce750-ec80-455e-b9a4-cd0cfb768...@xxxxxxxxxxxxxxxxxxxxxxxxxx>:



We are working on short range (5cm to 10cm) proximity detection.
First of all, I still think MEMS IR sensor is the way to go.
But it would take time to build, so perhaps next year.

Meanwhile, we are trying capacitive sensor using a 555 timer.
Based on input capacitance, the 555 output a periodic signal
monitored by a microcontroller.

The circuit works somewhat, but only when close to the
timer chip. The question is how can we isolate the trigger
pin and attach it to external detection plate.
Apparently, most of the electrostatic fields leaked between
the pins (trigger and ground) of the chip, so external plate
does not help much.

Thanks for any suggestions.

Have you considred ultrasonics?

Ultrasonics would be too expensive to implement.

Also, if it was possible to have some RF coil on the object, you could just
pick up the signal?

The object is an approaching hand or finger, which is a natural IR
transmitter anyway. The idea is to have micro-mirrors to focus on the
IR signal.
.

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