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Person Counter
   
 
   
The integrated circuit is a 4516 up/down counter.  
The diodes are illuminated by a beam of light.  
Diode 1 counts people.  
Diode 2 determines the count direction.  
The value of the resistors Rí depends on the type of diode used; you will probably need resistors in the range 100k to 1M.  
When entering the room, the beam illuminating diode 1 must be cut first; this causes the counter to count UP one.  
If (when a person leaves the room) the beam illuminating diode 2 is cut and while this beam is still cut the beam illuminating diode 1 is cut, the counter will count down one.  
The output can be used (with a relay and driver) to switch on a light when a person first enters the room and then to switch the light off when the last person leaves the room (maximum number of people, 15).  
   
Pins 1,3,4,5,12, and 13 of the 4516 must be connected to battery negative (see vero diagram below).  
The switch-on reset components (R and C) can have almost any values; try 100k and 1.5nF.  
Use I.R. receiver diodes with black insulating tape (or something similar) around them to block out extraneous light.  
Alternatively, you can put the diodes in a small plastic box, as shown below.  
   
 
   
Vero board, copper side  
   
 
   
Vero board, component side  
   
 
   
You can also add a simple circuit to make a beep each time the beam of light is cut, as shown below.  
   
 
   
The output can drive a small loudspeaker or piezo-electric buzzer or similar.  
The components C' and R' determine the time for which the buzzer sounds.  
R1 R2 and C determine the frequency of oscillation of the chip and therefore the pitch of the sound.  
The frequency is given by  
 
   
Vero board copper side  
 
   
Vero board component side  
 
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