Pinewood Derby Electronic Finish Line

[chriscc17]

Hi,

I want to make a finish line for those Pinewood Derby Races except I'm using Hot Wheel cars. There is only 1 company that makes one that uses photo sensors that isn't adversely affected by sunlight and it cost around $300.

So I want to make a mechanical one using tilt switches. As the car passes under the Finish Line it hits a loosely hanging tab that is centered in the middle of the lane. On top of the tab is a tilt switch which is activated from the cars impact.

There would be 4 lanes each one with a light above it. The first one to trigger flashes thus indicating the winner. Something along these lines:

The electrical theory behind most of the circuits in this class of is pretty simple. An LED, SCR and even Neon lamps are current devices. That is, they trigger at some specific voltage level and go into conduction and will remain in conduction until the current source is removed. Where there are multiple branches in a circuit sharing a limited current source only one device will have enough current to function. The first device to 'fire' uses the current and subsequent triggers to devices on other branches have no effect. In this way the first car to trigger the respective lane circuit gets the win.

I was wondering if someone might be able to help me with the electronic part of this project. I simply don't have $300 to spend on new one.

Thanks,

Wendell

 

[crutschow]

One of the circuits in this thread may work for you.

 

[MikeMl]

How about using 4 photo-resistors, centered in the tracks, looking upward. Each one connected to one channel of a**broken link removed**, and a CMOS quad latch with lockout gating, driving 4 leds?


ps, I was poking around on DigiKey, and found these sensors. I think they would be great for this project. $2.23 ea.

 

[chriscc17]

One of the circuits in this thread may work for you.

I've looked at those previously and the 12 volts of batteries to run it is too bulky. I don't have a permanent location so I need something easy to set up and transport. The $300 unit works on 3 AA batteries and will power the unit for around 12 hours.

How about using 4 photo-resistors,

Photo-resistor are affected by sunlight. From the $300 unit warranty information:

Purchaser using indoor sensors is responsible for assessing the ambient lighting conditions that will be present at the time of his derby, and taking necessary steps to insure proper operation. Purchaser realizes that the unit will generally not work outdoors during daylight, even in deep shade. Purchaser realizes that windows, skylights, and glass walls can make the indoor ambient light condition essentially outdoors and may affect operation adversely. Purchaser is aware that strong incandescent light (hot filament) may also affect operation.

 

[MikeMl]

Read the data sheet on the sensors I referenced. I think they are way better than LDRs.

 

[chriscc17]

I appreciate the response but I've already been down that road using sensors. A tilt switch is not effected by light so in that regard it's fool proof. Specfically I'm looking for a circuit using tilt switches and powered by 3 to 4 AA batteries or even a 9 volt battery.

 

[MikeMl]

Tilt switches have too much mass, and are slow to respond. Why not use a microswitch with a lever like these:

 

[crutschow]

**broken link removed** circuit from that thread uses CMOS logic and LEDs so it can be made to operate for a long period with 3 or 4 AA batteries.

 

[MrDEB]

You put the photo sensors ABOVE the track in a bridge. Shild the sides so ambient light does no affect. With the hot wheels, the bridge only needs to be a few inches above the track. Use IR emitters in the track
Glue a piece of track, the broidge etc to a board so it is all assembled as one section.
build the circuit that crutchow linked to.

 

[chriscc17]

Why not use a microswitch with a lever

I've been down that road as well. Although it would probably work fine with the bigger and heavier Pinewood Derby cars I couldn't get it to activate with the much smaller and lighter hot wheels car.

You put the photo sensors ABOVE the track in a bridge.

As I said I'm not using photo sensors. That is no longer an option although I appreciate your response. No matter what you do they are not reliable. To fully appreciate my situation picture spending hours organizing such an event. Everybody is there and excited to race only to have your finish line not work.

 

[Mikebits]

I've been down that road as well. Although it would probably work fine with the bigger and heavier Pinewood Derby cars I couldn't get it to activate with the much smaller and lighter hot wheels car.

As I said I'm not using photo sensors. That is no longer an option although I appreciate your response. No matter what you do they are not reliable. To fully appreciate my situation picture spending hours organizing such an event. Everybody is there and excited to race only to have your finish line not work.

They make real tiny micro switches that require very little mass to trigger and this would be the simplest approach. Anything else will get complicated. Perhaps you can look into capacitive sensors.
https://www.electro-tech-online.com/custompdfs/2010/04/capsense-wp.pdf When the car goes over the finish line a change in capacitance is detected, but again this seems a bit complicated.

 

[chriscc17]

This circuit from that thread uses CMOS logic and LEDs so it can be made to operate for a long period with 3 or 4 AA batteries.

2 questions regarding this circuit.

1) Can you simply replace the push button switches with Tilt switches as the activation device?
2) Also I see a master reset switch being used. I need for it to automatically reset each time without some switch having to be pressed.

For example the car hits the tab with the attached Tilt switch which causes the light to flash.
The tilt switch on the tab will rock back to it's original position automatically once the car passes through it. Based on this circuit would that action alone make it ready for the next race or would you need to modify it further?

 

[Mikebits]

Correct me if I am wrong but do not tilt switches require that they be tilted? Considering that a hotwheel weighs around 40 grams, how will you be causing this switch to be tilted? As MikeMI has suggested micros witches will be your best choice, especially from a mechanical mounting perspective. Detect Switches By C&K Components

Well that's about all I can suggest.

 

[chriscc17]

Correct me if I am wrong

From my first post:

So I want to make a mechanical one using tilt switches. As the car passes under the Finish Line it hits a loosely hanging tab that is centered in the middle of the lane. On top of the tab is a tilt switch which is activated from the cars impact.

This part of the project has already been made and tested. It works.

 

[crutschow]

If you elect to build the CMOS circuit in the link I posted, make sure you ground all the unused inputs to the two 4013 Flip-flops, the same as the schematic notes for the 4082, to minimize any erratic operation.

That circuit will use essentially no current when the LEDs are off (just leakage of the CMOS circuits which is very low).

You may want to lower the value of the 1k resistors in series with the LEDs if they are not bright enough. You may also want to use the high brightness type of LEDs.

 

[Mikebits]

From my first post:

So I want to make a mechanical one using tilt switches. As the car passes under the Finish Line it hits a loosely hanging tab that is centered in the middle of the lane. On top of the tab is a tilt switch which is activated from the cars impact.

This part of the project has already been made and tested. It works.

Your solution sounds like a kludge at best. With the micro switch you can simply cut a slot into the track with the switch actuator protruding through the slot ( Detect Switches By C&K Components ), and this can be built very robustly. There is no worry of false finishes due to someone bumping the table or any other false triggers, but I guess you have you mind made up so hope it works out for ya.

 

[chriscc17]

Your solution sounds like a kludge at best.

Is this type of feedback typical for this message board. If so that's very disappointing to someone who came here seeking help.

 

[Mikebits]

Is this type of feedback typical for this message board. If so that's very disappointing to someone who came here seeking help.

You have been given help by some very seasoned professionals such as MikeMI (Who has a PhD in EE) and have chosen to dismiss their input as well as mine, so not sure what you want.

 

[chriscc17]

so not sure what you want.

I certainly didn't come here to be treated like that. I feel sorry for others who come here seeking help with people like you responding. I certaintly won't come here again.

 

[Mikebits]

It was not my intent to cause you this amount of discomfort and I apologize for doing so. With that said, may I suggest you revisit some of the previously made suggestions.