LDRs are fine, set the threshold fairly high to avoid daylight
triggering and shield the LDRs by putting them into the end of a tube.
This will ensure that the only light they see is that from directly
infront. Otherwise use a photodiode or phototransistor, just as
effective...

Tony Nixon wrote:
>
> Hi all,
>
> Previously, I mentioned that I built an amphometer using a 16F84 a dual
> comparator and two LDRs. As a vehicle passed over the top of the LDRs,
> the light level change altered the output states of the comparators and
> the PIC calculated the speed from the difference in time. Pretty simple,
> and it was verified with high speed video and is quite accurate. The
> problem is varying light levels and the need to compensate for this to
> avoid false triggering.
>
> After much mucking about, I decided to still use the PIC section, but
> use 2 laser modules instead so that each beam can be broken as the
> vehicle passes. These are only $8 each for a 3-4.5V 5mW device complete
> with lens.
>
> Has anyone used LDRs as a detector for laser light, or should I use
> something else?
> --
> Best regards
>
> Tony
>
> http://www.picnpoke.com
> Email sales@picnpoke.com

Nino.
--
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* Antonio (Nino) Benci                               *
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