Track Building and BuyingDIY Electronic Timer with Four-Digit LED Displays for < $100

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First, I would like to say thanks to this community for the inspiration to build my own diecast racing track. I spent the week prior to Christmas building this track for my two sons (and my daughter likes it more than my wife might prefer too!) and it was certainly a hit when they found it stretching through the kitchen and dining room Christmas morning.

Pretty early on, I had my mind set on using some kind of electronic finish line. When it came time to figure out what exactly to use, I couldn’t justify the cost of the commercially available systems (I.e Microwizard, JUDGE, etc.) and, as I learned long ago from my other hobbies, I figured I could build a much cheaper, and maybe better, solution with all the same features.

To try and give a little back to the community, and maybe convince a few that electronic timing won’t break the bank, I thought I would show how I built my four lane electronic timer for about $100. This timer has the ability to display individual lane finishing order and times (four digits) and transmit these times to connected PC (with 0.0001 sec resolution, though I believe the tolerances in the placement of IR LED’s and phototansistros is probably the weak link at this point). I think a comparable kit from Microwizard would cost around $350. I believe you could also probably build something comparable to the JUDGE timer (including PC interface) by substituting single LED’s for the displays for well under $50 (maybe even as cheap as $25 using and Arduino clone and parts you might already have around).

Anyway, enough with the rational, and on to the details. At the heart of this project is an Arduino microcontroller. Just about any Arduino could probably be made to work as we are using fairly little I/O and resources. I happened to have an Arduino Uno laying around unused from another project which made this all the more attractive an option. The use of an Arduino means this timer can run in “stand alone” mode without requiring a PC as some of the other cheap timing options I found/considered would.

Due to the time crunch and because there was no need for reinventing the wheel, I bought a shield from David at miscjunk.org (www.miscjunk.org/mj/pg_pdt.html) that on top of providing breakouts for the critical I/O also contains some useful additions like a button to reset the timer, status LED, trim pot for setting the LED display brightness and installation points for the current limiting resistors. If I had more time, I might have built a custom board (and I am still considering doing so if free time allows) but his will certainly get you a functional timer very quickly.

I am running the Arduino code from miscjunk pretty much as is for now. I haven’t tried it, but he says it is even compatible with the GrandPrix Race Manager software that seems pretty popular with the pinewood derby crowd and certainly could be used here as well. As you might have guessed, however, I figured I could build it cheaper (I like a good challenge so we won’t consider what my time is worth) and better (i.e. usable by my young children), so I threw together a quick program to record and display the lane times on a PC.

I used the Adafruit 7-segment I2C driven displays suggested on miscjunk as it just makes it dead simple to run multiple displays, albeit at a pretty significant cost (nearly half the project total in this case). You could definitely do this cheaper if you have more time and the drive to do so. Maybe another good place for a custom board…

In summary, here are the majority of the parts needed:
Arduino Uno - $30 (or $11 for a clone)
Both the original and clone are available many sources. Maybe try to save on shipping by buying it from the same place you get other items.

PDT Timer Shield - $23
Here: www.miscjunk.org/mj/pg_pdt_pcb1.html

Adafruit 0.56" 4-Digit 7-Segment Display w/I2C Backpack - $10 per lane
There are multiple colors to choose from but I went with the red ones: www.adafruit.com/products/878
I actually bought mine here because they had a pre-Christmas sale and shipping was cheaper: chicagodist.com/products/adafrui ... ckpack-red

Infrared LED’s - $4
You could use a multitude of different parts here, including white LED’s as described at miscjunk because they put out enough energy at the wavelengths “visible” to some IR phototransistors to still work, but I preferred not having the visible light and used these: www.ebay.com/itm/20-x-Infrared-L ... 383wt_1034

Infrared Phototransistors - $4
Again, you could substitute a multitude of parts here but I used these: www.ebay.com/itm/10-x-Photo-Tran ... 442wt_1125

I bought some LED bezels ($4) to make mounting the LED’s a little easier but this is not required. I used these: www.ebay.com/itm/20-x-5mm-Bezel- ... 441wt_1125

The only other things you should need are a micro switch for the start trigger (I had one laying around) that you will need to adapt to your own starting gate design, some wood or other material to build the timer bridge for holding the IR LED’s and displays (hopefully left over from your track build or other projects) and some cabling and other miscellaneous parts to get everything wired up. Hopefully this isn’t more than another few $.

So all told, by my calculation, we are just under $100 for a two lane timer using an authentic Arduino and only $20 more than that for the four lane timer I built. Substitute an Arduino clone (or parts you already have around) and you can build either for less than $100.

Hopefully this inspires someone else to add electronic timing to their track and a rough guide for how to do it. Please feel free to ask any questions you have.

Here are a few pictures to show you how it all looks in action. If you have more than the hand saw and drill I was working with, you could probably make it look a lot nicer than mine as well

Starting Gate
Diecast Cars, Hot Wheels, Matchbox

Finish Ready State
Diecast Cars, Hot Wheels, Matchbox

Finish Order
Diecast Cars, Hot Wheels, Matchbox

Finish Times
Diecast Cars, Hot Wheels, Matchbox

Current state of the PC software (please ignore the unrealistic times and button mess…these are just for testing)
Diecast Cars, Hot Wheels, Matchbox

This is super cool...awesome. I'm glad you have come to help us out with getting a timer like this setup...very good & looking forward to more of your post.

Preacher

welcome aboard jojo... beyond my skill level but great stuff... thanks jo !

I agree with Smitty....most of this is above my skill set.

But I understand it, great write up and information!

Welcome aboard fellow Michigander. Now lets go racing!

I agree with Smitty....most of this is above my skill set.

But I understand it, great write up and information!

Welcome aboard fellow Michigander. Now lets go racing!

I would be willing to bet that if you can build your own track, you can successfully tackle this timer build as well. Some basic soldering is likely the only thing outside most folk's skill set, but that can be very easily taught/learned as I proved last week with my oldest son.

P.S. It looks like I am just up the road from you in Hartland...now you really don't have any excuse not to be able to do it

Cool builds and set up. Has it held up to moving it around? Also like that you choose two Corvette ZR1s for your starting gate photo!

Also like that you choose two Corvette ZR1s for your starting gate photo!

Of course you do

Keep those pictures coming...maybe some more of your track, or a video of an actual race?

Preacher

What race software are you using?

Preacher

Cool builds and set up. Has it held up to moving it around? Also like that you choose two Corvette ZR1s for your starting gate photo!

It has only had to move from the basement where it was built up to the kitchen and back down to its current home once at this point, so it is not much of a test, but so far so good. I built the timer bridge into a 23" long board that has the final piece of segmented track for each lane semi-permanently mounted to it. You can simply detach these last track sections and carry the entire assembly wherever needed. I have no doubt this would stand up perfectly well for real traveling if needed.

And yes, the kids have a bit of an affinity for Corvettes no doubt due, at least in small part, to Dad's job

What race software are you using?

Preacher

The software is a simple GUI I threw together using the wxWidgets library. Still a work in progress for sure.

Keep those pictures coming...maybe some more of your track, or a video of an actual race?

Preacher

I'll try to get some more pictures and a video this weekend.

[ Dad's job

Which team? If you dont want to make it public, you can PM me...

Awesome and thanks for uploading for the photos, great to see. I got an Arduino last year to try and make a finish line but never got it finished. I don't have any solder skills so mine remained on the breadboard. Your posting tells me that I was on the right track and is quite motivating.

I still don't have any fine electronics skills but I can fudge it...or just put a bread board in a project box, ha!

I assume you wrote the client software too? What did you use to build that?
I'm a programmer by trade so the Arduino programming was pretty easy.

If it's not too much trouble, could you list out all the tools you needed too? Getting parts is one thing but we all know that if you don't have the equipment then parts don't matter much.

You do good work! How are you detecting the finish? Where are the detectors and the leds? Are you looking for a broken beam of reflected signal?

Thanks,

Chuck

WECOME ABOARD CHUCK 72,
SURE SOME OF OUR SHARPER GUYS CAN HELP YOU OUT...

Awesome and thanks for uploading for the photos, great to see. I got an Arduino last year to try and make a finish line but never got it finished. I don't have any solder skills so mine remained on the breadboard. Your posting tells me that I was on the right track and is quite motivating.

I still don't have any fine electronics skills but I can fudge it...or just put a bread board in a project box, ha!

I assume you wrote the client software too? What did you use to build that?
I'm a programmer by trade so the Arduino programming was pretty easy.

If it's not too much trouble, could you list out all the tools you needed too? Getting parts is one thing but we all know that if you don't have the equipment then parts don't matter much.

I would certainly encourage you to give the Arduino powered finish line another shot especially if you have most of the parts required. Again, you could even skip the time displays if you don’t already have something that will work there and wanted to get it working really cheaply. Compared to many DIY electronics projects, there is very little soldering involved here and it’s all widely spaced through-hole components on the board. I have no doubt even the most beginner solderer could do it.

It a bit difficult to call either the Arduino or PC applications the client here as both serve in that capacity for difference purposes. Regardless, the PC application was built using the wxWidgets library. The Arduino code was originally written using the Arduino IDE (not by me) and I also used the Arduino IDE to make my changes and flash the micro.

The only major “tools” required for the electronics portion should be a soldering iron and wire cutters/strippers. A soldering “helping hands” tool would be a great addition but is optional. There are a few other electronics parts not mentioned in the first build post (mostly for connecting the displays and other parts to the Arduino) but this was done on purpose as I used a lot of what I had just laying around and if I was going to actually order things, would probably do it differently. I can help put a parts list together of what I might buy if I were to do this again if anyone wants/needs the help.

The track and timer “bridge” were literally built using nothing more than a hand drill, hand saw and T-square. If you have or could borrow a drill press and/or circular saw, I’m sure you could build it better/faster.

You do good work! How are you detecting the finish? Where are the detectors and the leds? Are you looking for a broken beam of reflected signal?

Thanks,

Chuck

Thanks for the compliment! The finish detector is made using infrared LED’s and phototransistors, and just as you suggest, detects a passing car when the beam between the two is broken. In my case, the LED’s are mounted in the bridge pointing down and the phototransistors are mounted from under the base board pointing up. There is probably no reason you couldn’t swap these around if so inclined. I found that the orange track used was quite infrared transparent so I didn’t even need to drill holes in it. If fact, I actually had to place washers above the photo transistors as the size of the hole drilled to mount them was causing it to be less sensitive than I wanted.

can one of you guys take the reaction time out of a drag tracks /expert racer set ?
having the cars and timer start when you hit the switch.... no reaction time, no rev limiters, no staging... just go ! ... ???

When I was building mine, I felt I had issues with the sensors getting crossed and they were also impacted by light levels in the room. My track is out in a sunroom so it can go from very bright to dim in a matter of minutes. I actually programmed the Arduino to take a light reading between resets so it knew what the trigger level was.

Your mentioning of the drilled hole causing problems might be what part of my issue was. I had a hole in the base board and the track for the sensor to shoot through but just was very unreliable. I only have a 2-lane track and wasn't even attempting to do a timer, just a simple "first on" quiz-style light.

Pre-Arduino, I had a friend solder me up a circuit for the beams but it also proved less than reliable. I'm not sure if those were IR or light sensors, it was a long time ago. Here's a shot from when I was building it. Used PVC thinking it would be a good conduit for the wires. I think the idea was valid but in the end it was probably overkill.

Diecast Cars, Hot Wheels, Matchbox

When I was building mine, I felt I had issues with the sensors getting crossed and they were also impacted by light levels in the room. My track is out in a sunroom so it can go from very bright to dim in a matter of minutes. I actually programmed the Arduino to take a light reading between resets so it knew what the trigger level was.

Your mentioning of the drilled hole causing problems might be what part of my issue was. I had a hole in the base board and the track for the sensor to shoot through but just was very unreliable. I only have a 2-lane track and wasn't even attempting to do a timer, just a simple "first on" quiz-style light.

Pre-Arduino, I had a friend solder me up a circuit for the beams but it also proved less than reliable. I'm not sure if those were IR or light sensors, it was a long time ago. Here's a shot from when I was building it. Used PVC thinking it would be a good conduit for the wires. I think the idea was valid but in the end it was probably overkill.

Diecast Cars, Hot Wheels, Matchbox

It looks like you were off to a good start and I would suspect that with just a bit of tweaking it would be perfectly reliable. My theory was that if I saturated the finish line with infrared light and "tuned" the sensitivity of the phototransistors with the orifice size, the ambient light intensity would have minimal effect. This theory seems to have panned out as it has worked just as well in the kitchen and living room with a significant number of south facing windows as it does in the basement with no natural light and varying amounts of artificial light.

Will it work outside?

Jojo,

Thank you for the post.  I have an Arduino starter kit and have just ordered the miscjunk PDT.  It is only sent with components for one lane.  What are the details of the resistor for each led and do you have more detail photos of the start gate?  I would like ours to be a stand alone track and use a manual release for my kids to physically start their races.

Thanks.

(Btw, any race videos from your track available to show?)

I am very impressed and would like to build your timer...my skills with electronics are very limited but I did build a two lane pinewood derby track and wired a couple micro lever switches to a stop watch for one of the lanes.  I think your timer would be awesome.  I was wondering if you may have a wiring diagram for it?


I'm not sure Jojo is around much since this post but try checking out the links he put in his article. The circuit boards he used might have some schematics or something...dunno...not really my area of expertise.

http://www.miscjunk.org/mj/pg_pdt_pcb1.html

Rickmc01
Ok, Thank You Redline derby !!!

Hello,

I'm very new to this sight and would like to build the timer. Please can someone tell me were I can get diagrams and instructions for the build?

Regards R 

Mopar_Mafia
User JoJo doesn't appear to be active on this site for awhile. You might try sending them a PM directly to see about the circuits diagrams.
Mopar_Mafia
Also the photobucket fiasco has left some carnage affect on this forum with broken links to photos. The website owner is working to fix

Please browse through the Finish Line articles and you'll find a lot more posts about making your own track timer. There are lots of different styles and techniques, most of which do include links and specs. 

All about finish lines
https://www.redlinederby.com/topic/finish-lines/c/3/2

As was mentioned, some of the images might be missing but all the links should still work.

Mopar_Mafia
Thanks B

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