[TriEmbed] TriEmbed Digest, Vol 39, Issue 20

[Shane Trent]

Chip,

I think you could set timer for the carrier generation to produced 15
cycles and have the interrupt from the IR detector stop the pulse
generation and set your result flag. So if you reach 15 cycles, the path to
the reflector was blocked indicating an object in the path. This would let
you keep your IR LED drive time as short as possible by turning off the
drive as soon as the carrier is detected. So if your detector is awesome
and locks in 7 cycles, it only get 7 cycles. If the detector needs 12
cycles, it gets only 12 cycles.

I wonder if heavy fog or rain would reflect enough of the IR to trick the
receiver into believing it could ALWAYS see the reflective target?

Shane

On Wed, Aug 24, 2016 at 11:57 PM Chip McClelland via TriEmbed <
triembed at triembed.org> wrote:

> Shane,
>
> That makes a lot of sense.  By looking at a specific time and for a
> specific carrier frequency (38 kHz), I can better see the signal against
> the background noise.
>
> So, instead of a phototransistor circuit, I would use an IR receiver
> sensor such as this one - http://www.vishay.com/docs/82474/tssp4p38.pdf
>
> To reduce the duty cycle, I would only run the 38kHz signal in bursts or
> 10-12 pulses.
>
> Will check this out.
>
> Chi
>
>
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