Count up/down?

[Zucker]

I would like to be able to count the number of people entering (count up)
and leaving (count down) a room. I was thinking about using two photocells
driven by two small lasers, spaced 6" to 12" apart, to detect if a person is
entering or leaving. If photocell A was tripped before photocell B, the
counter would count up. If photocell B was tripped before photocell A, the
counter would count down. My problem is that I'm trying to come up with a
circuit that can detect the AB or BA pattern. May be a circuit that can
detect the lag between the two photocell voltages? I don't know.

If anyone has a suggestion for this circuit or any other ideas, I would
appreciate it.

Thanks,
Steve

 

[Bill Bowden]

"Zucker" <zuckuss@comcast.net> wrote in message news:<bDLRa.85273$Ph3.9556@sccrnsc04>...

I would like to be able to count the number of people entering (count up)
and leaving (count down) a room. I was thinking about using two photocells
driven by two small lasers, spaced 6" to 12" apart, to detect if a person is
entering or leaving. If photocell A was tripped before photocell B, the
counter would count up. If photocell B was tripped before photocell A, the
counter would count down. My problem is that I'm trying to come up with a
circuit that can detect the AB or BA pattern. May be a circuit that can
detect the lag between the two photocell voltages? I don't know.

If anyone has a suggestion for this circuit or any other ideas, I would
appreciate it.

Thanks,
Steve

Space the photocells closer so that both will be blocked when
someone walks by. Use one photocell to control the up/down line
of the counter and the other to provide the clock pulse.

When a person walks by and crosses the clock cell first, the
counter will advance, and when they walk by the other direction
the counter will decrement because the up/down line was changed
before the clock arrived.

-Bill