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Old 03-21-2011, 03:41 PM   #1
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Wiring a pinewood derby pressure sensor


So here is what I want to do.

I would like to create a three-sensor circuit that would let me know the winner of a pinewood derby race. Essentially it would be three pressure plates that the cars would hit at the bottom of the track, but I would like to figure out a way to show racing results (1st place, 2nd, 3rd) using those same plates. Is this going way too complicated for a pinewood derby? If not, any ideas how to wire it to work like I want it to?

- Nutaris

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Old 03-21-2011, 04:11 PM   #2
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Wiring a pinewood derby pressure sensor


In the vicinity of 50 years ago that I built my own racer, and we don't have kids, so my recall is a bit sketchy, but it sounds like a fun project. Better, or at least more, ideas will surely come along, but since you'll probably want to keep it relatively simple, the first thing that comes to my mind is long handled toggle switches. Assuming that you will step it down to 12 volts, or something in that area, you should be able to pick up a transformer and some switches at a hobby shop that handles electric trains, etc. Or, if you wanted to add a classic DIY touch to it, you might try standard old mouse traps, with some manner of trip device that would keep fingers out of harms way, maybe a piece of plexiglass over the traps, and some brass tacks or screws for contacts.

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Old 03-21-2011, 04:49 PM   #3
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Wiring a pinewood derby pressure sensor


Happened to think after the fact that I maybe should have explained a bit more. Anyway, a transformer, to reduce 115 volt AC to 12 volt DC, three circuits, with a switch and light on each circuit. Pretty straight forward. Also thought that since you mentioned pressure plates, you could construct something like two pices of wood with with a piece of copper on each one, and springs in between them, to function as a pressure switch. You'd have to take it from there, to see how it would fit your track, and figure how much spring you need for that amount of weight. Maybe the two pieces form a V, so that the cars would ride up onto it as the reach the end of the run. Wow! This is one of those times when I wish we had kids. On the other hand, we still have more than enough to keep us busy, so I'll go do something. Good luck, and have fun!
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Old 03-21-2011, 05:30 PM   #4
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Wiring a pinewood derby pressure sensor


Another answer depending on your technical prowess is to just use a microcontroller (an arduino for example) and embed some optical detector/phototransistors (http://www.sparkfun.com/products/246) in the bed of each lane at the finish line. Then have your controller watch the analog values coming from the 3 detectors and trip when they cross a threshold (a car crosses the sensor).

All the nice extras you mention ie displaying finish position etc would be easy to implement with this kind of a framework. This could all be done with more traditional electronics and ICs but the microprocessor way would be pretty simple.

As an added perk you could even set it up to display each racers actual run time.
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Old 03-21-2011, 07:37 PM   #5
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Wiring a pinewood derby pressure sensor


Great ideas! I am getting really excited about this. This is bad though, I'm getting the itch to build all kinds of things now.
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Old 03-22-2011, 07:04 AM   #6
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Wiring a pinewood derby pressure sensor


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Originally Posted by Nutaris View Post
Great ideas! I am getting really excited about this. This is bad though, I'm getting the itch to build all kinds of things now.
" Sounds a bit much for the day of fun for the scouts".
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Old 03-22-2011, 11:00 AM   #7
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Wiring a pinewood derby pressure sensor


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" Sounds a bit much for the day of fun for the scouts".
I agree. Why not just use a ribbon or tape down a finish line?
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Old 03-22-2011, 11:09 AM   #8
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Wiring a pinewood derby pressure sensor


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Originally Posted by b_corwin View Post
Another answer depending on your technical prowess is to just use a microcontroller (an arduino for example) and embed some optical detector/phototransistors (http://www.sparkfun.com/products/246) in the bed of each lane at the finish line. Then have your controller watch the analog values coming from the 3 detectors and trip when they cross a threshold (a car crosses the sensor).

All the nice extras you mention ie displaying finish position etc would be easy to implement with this kind of a framework. This could all be done with more traditional electronics and ICs but the microprocessor way would be pretty simple.

As an added perk you could even set it up to display each racers actual run time.
Personally, I like this idea. Exactly what I was thinking when I started reading the thread. Is it overkill? Sure but who cares? It adds some fun and excitement to the situation. Isn't that what it's all about?
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Old 03-22-2011, 11:40 AM   #9
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Wiring a pinewood derby pressure sensor


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Personally, I like this idea. Exactly what I was thinking when I started reading the thread. Is it overkill? Sure but who cares? It adds some fun and excitement to the situation. Isn't that what it's all about?
" Not really, might take too much attention away from the kids experience"
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Old 03-22-2011, 12:31 PM   #10
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Wiring a pinewood derby pressure sensor


I tried (with the help of an EE and a couple friends) to make a pushbutton thing that would light up whichever button was pushed first (like on Jeopardy). It never worked properly.

Anyway, is the winner based on the wheel or the bumper? If I was going to do it, I think I'd use optical sensors instead of pressure switches. It's a lot less complicated because mechanical sensors need to be "de-bounced".

The difficulty in our project was locking out the circuit after the winner was discovered. We were using a micro controller, but we couldn't get the code to fit. It was a long time ago.

If you could find some kind of home Jeopardy style controller, you could modify the buttons to whatever kind of sensors you want.
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Old 03-22-2011, 12:47 PM   #11
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Wiring a pinewood derby pressure sensor


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Personally, I like this idea. Exactly what I was thinking when I started reading the thread. Is it overkill? Sure but who cares? It adds some fun and excitement to the situation. Isn't that what it's all about?
To be honest, these days I am not even sure if I would call it overkill. I can buy an Arduino clone for 11 bucks and it saves me a boat load of time.

Pyper brings up good points but they are not very large obstacles these days.

The "fitting" the code onto the board should be a non issue. I have written far more complicated pieces of software than this that fit with no issue. The 168 or 328 cores of the Arduinos store 16/32kb respectively.

Debouncing mechanical switches can be sorted out in hardware or software without much issue.

I also agree though that if you have no familiarity with doing this type of work it might be overkill in terms of effort for a day of fun with the scouts. But if you happen to have a friend or know someone with some experience, this thing could be built in an afternoon over beers.

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Old 03-22-2011, 12:48 PM   #12
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Wiring a pinewood derby pressure sensor


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I tried (with the help of an EE and a couple friends) to make a pushbutton thing that would light up whichever button was pushed first (like on Jeopardy). It never worked properly.

piece o' cake. all it takes is the buttons, a few relays, the light , and power source. I would not mention your EE friend had trouble with this.

If you want to get a bit more complex, you can add some relays so you can control multiple colored lights at each lane or something a bit simpler would be to illuminate a number readout next to a "1st" "2nd" "3rd" on a mini-tower similar in style to what is used at the Indianapolis Motor Speedway.

and that type of system would be simple without a plc but just good old fashioned relay logic. The plc would allow more types of sensors and more bells and whistles.
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Old 03-22-2011, 02:48 PM   #13
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Wiring a pinewood derby pressure sensor


http://www.hmpg.net/pinewood/


There are also several commercially available turn-key timing kits available.

I would use optical sensors (cars break a beam of light) instead of pressure sensors. light shines from a pedestal down through a hole in the track to the sensor. That way, you still have the cars "run out" instead of hitting a wall or other sensor at the end to stop the clock.

This can be a fun project either way. Let us know how it turns out.
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Old 03-22-2011, 03:01 PM   #14
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Wiring a pinewood derby pressure sensor


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Originally Posted by b_corwin View Post

I also agree though that if you have no familiarity with doing this type of work it might be overkill in terms of effort for a day of fun with the scouts. But if you happen to have a friend or know someone with some experience, this thing could be built in an afternoon over beers.

B
arduino clone for $11? where can I find this? and which arduino is it meant to replace?

I would suggest that something such as this in itself might be a project for scouts. In my days as a scout it was a lot of whittling and nature projects but given society today, I would think an electronics project would be a good direction to take the scouts.
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Old 03-22-2011, 03:19 PM   #15
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Wiring a pinewood derby pressure sensor


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arduino clone for $11? where can I find this? and which arduino is it meant to replace?

I would suggest that something such as this in itself might be a project for scouts. In my days as a scout it was a lot of whittling and nature projects but given society today, I would think an electronics project would be a good direction to take the scouts.

$13 if you buy one. I buy them in the bulk packs

http://shop.moderndevice.com/products/rbbb-kit

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