I am new to this site, hello! I see some other posts about using the PDT timer from http://www.miscjunk.org/mj/pg_pdt.html. This is the plan I used. I ordered the circuit board pack and was able to use the blueprint from that site to get all of the other parts needed. This was my first ever electronic building project so I did have some struggles but David on the site was very helpful and I was able to get it running.
Sorry I don't have any build photos, it just wasn't something that I thought about while I was building it. I have included some of the finished product though.
I built the track out of plywood and attached 4 foot sections of Hot Wheels orange track to the sections of the plywood at the beginning and the end of the track by putting small screws through the end to hold it. It's all connected in the middle with the connectors that came with the track. I Built supports out of 2x4s to put the sections of plywood on. The start of the track is 4 feet tall. The track was originally 24 feet long with the slope going from 4 feet at the start to the floor at the end. I put the finish line at 20' 7.5" which is a scale 1/4 mile and ended up cutting off around 2 feet of the total track to save some space so now the end is about 3.5 inches off of the ground. Though I leave it up permanently I built it so that it can be easily disassembled. The plywood is in 4 foot sections with each section being held to the 2x4s with two screws in each end. The stop for the cars is a 1lb bag of rice sewn into some duck fabric which I then screwed to the track on the edges. It works really well for short cars which slide under the fabric and come to a safe halt. Taller cars, like the Kenworth Big Rig, tend to hit it and go flying off. Most cars aren't that tall so it works really well most of the time.
The timer I built to nearly the exact specifications found on the site and I used the exact code found on the site to make it work. The only adjustment that I had to make was to set the code up for 6 lanes as I believe when downloaded it is set up for 2.
For the start gate I opted for a hinged garage door style which I made out of some scrap wood and a small piece of scrap plexiglass. I went with this option because after much testing I decided it gave the most fair start regardless of car height. I've noticed that with tracks that have a start gate that drops out from the bottom taller cars seem to have an advantage, though it may be minimal I wanted to reduce this. As you can see in the photo the door is completely out of the way and we have a fair start.
I opted to not install the solenoid to open the start gate. Instead I put a long screw part of the way into the door and use it as a lever to flip it open with my thumb. I did put a start switch on the door which starts the timer when the door is opened. I find that it works quite well though I may install the solenoid at a later date.
The housing for the finish line is again just some scrap wood. I cut holes in a piece of plywood and mounted the LCD Displays to it. Being inexperienced in electronics this build took me quite a bit of time but I am very satisfied with the result. I plan to add some numbers on the lanes and next to the LCDs in the future so it's more clear which LCD goes with which lane but for now it works and I enjoy testing cars out down it.
I made a video showing all of this over on my YouTube channel if you're interested in checking that out here is the link.
Thanks for taking the time to read this post!