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DIY Electronic Timer with Four-Digit LED Displays for < $100

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redlinederby 2/15/14
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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.

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chuck72 2/24/14

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

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model40fan 2/24/14

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

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jojo 2/26/14

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.

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jojo 2/26/14

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.

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model40fan 2/26/14

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 ! ... ???

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redlinederby 2/26/14
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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

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jojo 3/5/14

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.

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Milton-Fox 3/5/14

Will it work outside?

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iswingping 6/10/14

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?)

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Rickmc01 1/28/16

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?


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redlinederby 1/28/16
Site manager

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

  • Ok, Thank You Redline derby !!! — Rickmc01

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