Once you've built your track, you'll of course want to know how fast you're going, and you won't want to count laps in your head while you're trying to keep ahead of the guy in the next lane. While you can use something as simple as a wristwatch and notepad, you'll need an impartial 3rd party use them, and were are you going to find somebody who's impartial once the racing heats up!
Computer timing and scoring was once price prohibitive to all save Formula 1 & CART (USAC & IRL apparently still haven't mastered it), but is now available to anyone for under $100. Old PC's (8086, 80286, 80386 and even 486s) are available for zero to $100 from garage sales, want ads, recycles, pawn shops, surplus stores, any offices (with Y2K induced upgrades they'll be even more plentiful). A 286 is more then capable of keeping track of a two or three lane home track with DOS based software. A word of warning, if you're paying more then $5 for your PC make sure everything's working well before you buy. If it's not, don't fix it, don't haggle, just move on, there's plenty of other old clunkers to choose from.
Slot car timing software is available on the internet from a number of variety of sources (including us!) for any price between free and $200 depending on how many features you want to pay for. Or if you enjoy it, you can write your own (as we've done). Writing your own software can be just as rewarding (and frustrating) as building your track, and it's more likely to fit your particular needs.
The only tricky part is connecting your track to the computer. Here's an accumulation of the techniques we've tried and what we've learned.
General rules for all methods:
Place your detection mechanism at your start/finish line.
Make sure the line of site from all the controller positions to the
start/finish line is clear.
Ideally if someone's going to operate the computer for a race, that
person should be able to set up the cars at the start line.
Make sure that a car in a wild power slide can't trigger another lane
(don't place the detection too close to corners).
Make sure that an unscrupulous competitor can't trigger the detector
manually (you'd be surprised....).
Dissected mice.
First Bryan cruelly took apart a variety of species of mice to have the car trigger a mouse click that would be received by a PC. This didn't work out too well for a number of reasons:
We were attempting this with a PC that had Windows installed and of course we lost the use of the mouse for anything else.
Cars of different weights, sizes and speeds didn't always trigger the same every lap.
We've found this last point is generally true of all mechanical triggers.
Probably the simplest solution mechanically. Take an area of track (2-3 inches is enough) and isolate it from the power source (using the same method to loop the security under the track as described in the construction section). Connect this dead zone to your PC and when the car goes over the deadzone the brushes will make contact with your tape through the car and close the circuit.
A couple of points to consider however:
Because this section isn't powered, if the car goes to slow over that section, it will "stall". You also have to place the start/finish line after the timing section for the same reason.
Any timing software has to be able to cope with multiple signals within a very sort time and treat them as only one. While the car is traveling along a 3" deadzone, it may bounce and send two or more signals to the PC.
After 2-3 years of reliable use, the deadzone started to receive signals
when a car was under power yet no where near the zone. Our theory is that
over the years the aluminum tape carrying the power started to oxidize
and the resistance increased until arcing to the deadzone offered the electricity
a more attractive escape route. (which just demonstrates how little
you need to know about electricity to build a slotcar track). We took
this opportunity to experiment with other solutions.
This offered the greatest promise and provided by far the greatest frustration! Small, cheap, surface mounted imiter-detector pairs placed in the track on either side of the slot. The cars' slot guide broke the infrared signal for a short time as each car travels over them.
After years of farting around with them, I finally had somebody from
Radio Shack draw me a simple wiring diagram on the back of a cash register
receipt. I took that home and wired it up on a home made circuit board
in a matter of minutes, hooked it up to a 5V power supply and my timing
software and it worked just great! AND WE'VE NEVER BEEN ABLE TO MAKE ANOTHER
ONE WORK SINCE.
Photocells
Our timing systems have evolved over the years collimating with .
Photocells are sort of a medium-tech solution. Credit this idea where credit is due: Bryan's 88-year-old mother. If you've got a night light that's smart enough to turn itself on when it gets dark you've got a photocell. They're basically small light sensitive resistors, the less light the greater the resistance, Radio Shack sells them in packs of 5. These are placed in the bottom of the slot facing upward (towards the light of course) and the car travelling over the cell blocks the light and momentarily increases the resistance in a signal sent to the PC.
The Photo Cells have proven to be the simplest solution too, as, much
to the chagrin of our nearest Radio Shack supplier, no other electronic
bits and pieces are needed (and subject to failure), such as transistors,
diodes, IC's, capacitors etc. Photo Cells are very easy to test and
measure with a simple volt/ohmmeter in order to establish if the y are
working or not (we havent had a failure yet!).
Connecting the Photcell to the Parallel Port (LPT1) has provided the best reliability with a near perfect success rate. Our game port connectiion still gets occaisional errant hits which we have not been able to eliminate.
One great benefit is Pit Stops! Even the greenest rookie can stop the car over top of one of these sensors enabling you to simulate pit stops for enduro racing (check out our LeMans timing software!)
Of course nothing is perfect:
Different locations have different levels of ambient light and may need an additional light source in order to give the photocells a reliable amount of light. An aquarium light works well or a small desk lamp.
Place the sensors where the cars aren't in a power slide or else the car from one lane could trigger the sensor in the adjacent lane.
The sensors will send a constant signal except when a car blocks them,
so your timing software will have to recognize the absence of a signal
as a car.