04-05-2012, 12:06 PM
The People Counter
PeopleCounter_by_AndrewMansson_Fall2000.pdf (Size: 34.14 KB / Downloads: 40)
Purpose
The purpose of the people counter is to count people. The
application that I see that it is most suited for and what I had in mind when
making it, is to keep track of the people in a room. If there is more than
one person in the room, then it turns on the lights in the room.
The Circuit
The circuit uses a combination of analog and digital components.
The way that I planned to count the people was to use two beams of light.
If you broke the beams going in one direction, the circuit would add one.
If you went in the other, it would subtract one.
I used an Schmitt trigger to convert the analog signal I got from
the light sensitive diodes. The diodes put out a voltage in the range of .
volts with no laser beam and .4 with a laser beam. I did not have a large
window for the hysterisis. I had to use a large resistor when
bootstrapping the output back into the input.
Next, I used an OR gate that interprets the out puts of the Schmitt
trigger and I used this output to trigger the rest of my circuit. This trigger
the D-flip-flop, which recorded the value of one of the outputs of the
Schmitt triggers. This value the D-flip-flop recorded is passed to the updown
counter. This tells the counter whether to count up or down when
triggered.
Then, the way that I triggered the counter was by using an inverter
on the trigger coming into the D-flip-flop. I took the output from the
inverter and used it to trigger the counter. The counter triggered on the up
slope so this worked well.
Finally to tell if there was someone in the room, I sent the output
of the counter through a set of OR gates which was connected to a light
emitting diode. If there is anyone in the room it would turn on. Also I
had the out puts of the counter hooked up to a display so that I could keep
track of how many people were in the room.
Conclusions
Everything ended up working just fine. But I did have some
problems with bouncing but the Schmitt trigger cleared all that up.
Other uses for this circuit could be to measure velocity of things
that pass through the beams and the length of the object in one
direction. One of the biggest problems was lining up the beams of
light to get the right voltage levels. Once I got that right, it went
very well.