Class Project

I have to construct a small project for my final, I decided to make something similar to the parking lot counter, but for a room. Like with the parking lot coutner, of a certain amout of cars come in, and the lot is full it will deny entry. With the room,

I want it count how many people come in, and out.

When someone enters the room, the light will come on.

When the room is empty, it will shut off all the lights.. tV. etc

I think I may need two sensors because I will only have one door. SO it would be hard for one sensor to tell if some body is leaving , or entering the room

What kind of parts would I need, again its a small project

Technically, what you want to do, is a quadrature function, and doesn't require anything more than two 'sensors', and an off the shelf 'preset counter' that accepts quadrature inputs and has a contact closure output.

One door, means entering and exiting from the same point. Right. So you need a way to determine direction.

Most doors open to the inside.. this is good.

You need a sensor to determine if the door is open, and one on the outside which is 'human presence detect'.

The quadrature function is like this... If 'Human Presence Detect' (HPD) is TRUE when 'Door Open Sensor' (DOS) goes true, then someone is entering.
On the other hand, if 'HPD' is FALSE when DOS goes true, someone is leaving.

Yeah, only one door, so I needed somethign to determine direction

I wast thinking about using two sensors, one on each side of the doorway. Then using a counter, so say if, some body walks in, they set off the First sensor, whichs puts a timer off delay, on the 2nd switch, so it know ssome body comes in , and the same for when they leave.

You have a good idea too.What would i use for the HPD. a motion sensor?

rdrast said:

You need a sensor to determine if the door is open, and one on the outside which is 'human presence detect'.

The quadrature function is like this... If 'Human Presence Detect' (HPD) is TRUE when 'Door Open Sensor' (DOS) goes true, then someone is entering.
On the other hand, if 'HPD' is FALSE when DOS goes true, someone is leaving.

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Won’t quite work. Problem is what if the door is left open? Then you wouldn’t be able to tell what direction the person is traveling in (entering or leaving). So you need to have a sensor on either side of the door. Whichever sensor breaks first tells direction of travel. Now take the door into consideration. Adding a door sensor is the best way. I would use what they use for alarm systems, a magnet and reed switch.

Kinda like counting cards....

So lets say you have two retro-reflective photo sensors. Place them at the same level but spaced out about 12" horizontally. This would provide the differential between comming and going.

So as you approch te door from the inside going out sensor 1 will latch "out" bit. Then when sensor 2 is tripped the latched "out" bit will direct to count down, then reset the latch. Visa versa for comming in. The counter will count up and down as people are entering and leaving, but when the count hits zero, you turn off the lights.

May also want to put a timer in for shutting off lights/TV. Lets say a person walks out, then turns right around again, it would be very stressful on equipment shutting off and on.

Just my $.02

just_lionel said:

May also want to put a timer in for shutting off lights/TV. Lets say a person walks out, then turns right around again, it would be very stressful on equipment shutting off and on.

Just my $.02

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You mean like running for a beer during the commerical break??

elevmike said:

You mean like running for a beer during the commerical break??

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LOL, thats a good point. Also, if the person is me, I always forget something when I leave, and remember once I walk out the room.

Use to have a bad habit of shutting the door behind me leaving the house and having the keys inside, locked up. I've broke into my house so many times now its not even funny.

What will be the basis of your grade? If it will be strictly based on your ability to program the PLC to perform the assigned task, then go for it. If a portion of grade will be based on whether or not your system is practical, be prepared to explain how your system will be an improvement on a simple motion detector.

You should also include an analysis of the modes of failure of your system and their consequences. For instance, if it is possible for two people to enter or leave the room side-by-side and the accumulated count is no longer accurate, what are the consequences of both system count greater than actual count and system count less than actual count. What will you need to provide to recover from a system failure?

The ablity to program the PLC, is basically what I graded on.

madthoughtz said:

The ablity to program the PLC, is basically what I graded on.

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Not a whole lot of fancy programming involved with this one. On the outside your looking at maybe ~100 instructions. Your instructor might be impressed with the differental count based on which input comes on 1st, but the rest of it is pretty simple. I would guess that the instructor would be looking for you to use whatever instructions have been coverd in the class so far. This project would require just 2 inputs, one out put, a few timers, and one up/down counter. The counting also could be done with ADDing or Subtracting 1, or INCrementing & DECrementing 1. Even though the idea has some practical merit, it's not going to demonstrate a whole lot of programming prowess.

I havent doing any Adding or subtracting/Incrementing or Decrementing instructions so far. Truthfully the only PLC programing I've done so far is on LogixPro.. right now I'm on the traffic light.

So two retro-reflective photo sensors would be the best inputs?

Keep in mind I'm not using a real room.

Yes, the two reto reflective eyes would be the two inputs used to determine if someones entering or leaving the room. I've seem retro-eyes at Radio Shack, so they arnt that hard to find. If your PLC has 24vdc inputs you can use theses mabey: http://www.automationdirect.com/adc/Shopping/Catalog/Sensors_-z-_Encoders/Photoelectric_Sensors/18mm_Round_-_NonMetal_(MS-z-SS-z-FA_Series)/Retroreflective_(SS-z-FA_Series)/SSP-0N-4A

You need to determine of your PLC has sinking or sourcing inputs to choose the right sensor. Dont worry about the sensor right now, you can use a jumper to simulate the sensor action on the PLC inputs.

So for the logic: As someone is passing through the doorway, they will trip sensor A then B, or B then A depending on direction. You can use that sequence to determine to count UP or DOWN. For now presume the sensor inputs will overlap with one another. For example if you are counting boxes on a conveyer; if the boxes are 12" long and the sensors are space 6" apart then the two signals will be on at the same time for at least 6" of the box travel. The key is, which sensor went on 1st, and which went on last? So each sensor would be represented by an internal relay. Lets call them IR-A and IR-B. So if Sensor A goes on 1st then IR-A would come on and prevent IR-B from comming on when sensor B goes on, however Sensor B would cause a count in the approperate direction.

This is where I start getting dangerously close to doing your project for you, so you'll have to try to give it a shot and post some code, then we'll go from there...This part is kind of a challange for the beginner, but not too bad. Just draw it on a paper and work it from there.

I've just made it easier.
Instead of counting up, and down. All I need is to count how many people enter the room. Somebody wants to know how many people enter the Libary a day. I will still need 2 inputs so I can determine if somebody is entering the room, instead of leaving. I guess I would have to add a counter, to count the school hours, so i can use that to reset the count.

So all I need is two sensors (reto reflective eyes), and something to display the count.