# Parking lot counter

Discussion in 'Homework Help' started by SpeechMan, Feb 11, 2009.

1. ### SpeechMan Thread Starter New Member

Feb 11, 2009
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Like mentioned in the title, I need to design a parking lot counter. Problem is that I have no enter/exit input, instead I have sensor placed on each lot, which will activate if the lot is occupied. The system would consist of 8 areas, each having 8-19 lots and own separate display (either green/red or 7-segment), so I need binary output of the amount of occupied lots.

Anyone have any idea how this could be made? I've been searching net for hours but came up with nothing.

2. ### RiJoRI Well-Known Member

Aug 15, 2007
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Given the constraints, I do not believe it can be done. You will need some type of sensor for the entry & exit point(s).

--Rich

3. ### KMoffett AAC Fanatic!

Dec 19, 2007
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By "lot" do you mean an area with multiple, marked places to park cars? Or, does "lot" mean just the marked place to park one car?

Ken

4. ### tuborggg Active Member

Jan 3, 2009
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If I' missing something, tell me...
Otherwise, you have the sensors for each parking space - count how many of them are occupied. (a register of #number of sensors width, and a counter for how many '1's you've got at a given time).
also, each bit of the register will be connected to a led which will be on when the bit is '1'...

5. ### SpeechMan Thread Starter New Member

Feb 11, 2009
3
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@KMoffett
By lot, I mean the space for single car, so on each space there would be a sensor watching if the position is free or used.

@tuborggg
Idea is that every space for car would have a sensor, that is the input.
For output I have 3 variations.

1) map with led for each space
2) Traffic light system, green for more than 5 available spaces on certain area, yellow for 1-5 available spaces and red for all full.
3) 7-segment display that shows how many spaces are available.

Option 1 is easy, just by simply connecting each sensor to a led.
But for options 2 and 3 I need a system that counts how many sensors are '1' and then outputs that amount as either BCD or binary digit. That is my biggest problem at the moment, I know it can be done, as many parking areas have such system and some of them don't require a PC, but I haven't found any schematics or info on how the system actually works.

I can easily create the necessary compare and decoder systems for the output, but the biggest problem is that for those I need that BCD or binary digit.

6. ### Ron H AAC Fanatic!

Apr 14, 2005
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Sounds like you have unary inputs, and you want to add them and convert the result to binary or BCD. Is that a fair description of your problem?

7. ### SpeechMan Thread Starter New Member

Feb 11, 2009
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Exactly. Unfortunately, I don't know have any idea how to do this.

8. ### Ron H AAC Fanatic!

Apr 14, 2005
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A microcontroller might be the simplest way. If you want to use discrete logic, the first thing that comes to mind is a multiplexer to scan all the inputs, with its output connected to the count enable of a binary counter. Each occupied space would cause the counter to increment by one. Unoccupied spaces would inhibit the counter.
You would need another counter to create the address inputs to the multiplexer.

9. ### Ron H AAC Fanatic!

Apr 14, 2005
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How do you reset this scheme if the count gets screwed up?

10. ### Wendy Moderator

Mar 24, 2008
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A simple camera, where pixels for each space is monitored. If they are off colored (ie, a car is parked there) then it is a 1, if it matches the color profile for time of day it is empty, a 0. It would still be easy to spoof, but cheap.

11. ### Ron H AAC Fanatic!

Apr 14, 2005
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You may be correct. I suppose it depends on the lesson that was intended. If my students did not consider the count getting screwed up, I might tell them that they had not considered failure modes. Good engineers try to foresee possible failure modes, and protect against them or provide a workaround.
That is a reasonable workaround. In the absence of nonvolatile memory, it would require a little work to restore the count in the event of power failure.

12. ### Ron H AAC Fanatic!

Apr 14, 2005
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I'm a 67 year old retired EE. I have never taught. I guess we could each learn from the other.