Scale Model Racing - Lap Counter

Introduction

Not wanting to spend a small fortune on commercial timing equipment as well as not wanting to burden our R/C cars with the added weight of a transponder, especially our micro-cars like Mini-Z's and Radi-Can's, we decided to build a low cost lap counting system. Right from the onset, allow me to say that neither the software or hardware are our creations. We simply scoured the Internet and came up with all freely available software and schematics. OK, I changed the lasers to LED's. but that's it. And of course, anyone wanting to improve on what we have presented...by all means go for it !! Let us know if you come up with something good.

Disclaimer

Although we haven't had any problems with any of the hardware or software described on the page, that doesn't mean that you won't have any problems. Therefore, by using any information presented on this page you agree that you do so at your own risk. So, if you set your ass on fire or blow up your PC...it's your own fault and not ours. If you think that we should be liable for anything like that, please leave this site NOW. We put this info together to help further the enjoyment of our sport.

Functionality

The principals of operation are very simple. There are 4 LDR's or Photo resistors placed in a "tower", stacked one on top of another, spaced about 2 inches apart on one side of the track. On the other side of the track there are 4 super bright LED's focused directly at the LDR's or photo resistors. Each vehicle has an antenna with a solid "flag" attached to it. The flag is made from medium density cardboard or posterboard. Each vehicle's flag corresponds to an LED. For instance, if the first LED/Photocell pair is at 4 inches from the track surface, then the antenna from one car would be set to 4 inches above the track surface. The next pair would be 6 inches, next car 6 inches, etc. What we want is the flag to break one LED beam. When this beam is broken, the resistance is changed and is captured by the control circuit which then sends a signal to the PC and the software interprets the resistance change as a lap. The sensitivity is adjustable, so you can make sure that only flag interruption causes a lap to be registered and not the antenna itself.

Parts and Software

Let's start with the software. I chose to use a DOS based program since I had a 386-25MHz sitting around. (Yeah, yeah, I know, the Smithsonian was looking for one of those!) The 386 is running clean, that is to say, no Windows, just DOS. It is amazing how fast it appears to be when Windows isn't installed. Anyway, the software is free and you can get a copy here.

The hardware is very easy and I'm not gonna make the explanation difficult either. The layout is from SlotRace.Com.

Click on "Schematic" to see the layout.

DB9 Female

Schematic

We bought everything from Radio Shack. In the layout the LM324 is separated into quarters. Each quarter serves a car. You will need:

• LM32 4- Qty. 1
• 100K-ohm PC Mount Potentiometer - Qty. 4
• 200-ohm Resistors - Qty. 4
• 10K-ohm Resistors - Qty. 8
• LDR or Photocells - Qty. 4
• Hi-Brite LED's - Qty. 4
• DB9 Female - Qty. 1
• Perf-Board, wire, solder

You will also need to have +5vDC. We used an off the shelf plug-in transformer. We also ran it with batteries. 4.5 to 6vDC (3 to 4 AA cells) worked fine. Using the schematic, lay everything out, wire it up and solder.

Making The Tower

Here, you can be as creative as you'd like to be. We've included a line drawing of a basic tower. But, like we said...go balistic. You could make the tower look like one of those cross-over bridges you see at real road courses.

Here are some more line drawings: Hold On, I'm Trying To Scan Some REAL Pictures In.

We hope that you can use the info presented here. This setup is in no way "perfect". But, It does serve it's purpose of being an extremely low cost lap counter. Did some of the cars slip past without being counted? Yes, but by adjusting the sensitivity, and placing the tower right in or after a tight turn, we got 100% counting! Other problems? Well, there was some "interference" from the LED's. One of the eggheads over here said it was called "scatter". Where the light from one LED is recorded by a photocell that shouldn't be recording it. Anyway, using thin pieces of cardboard, we made "blinders" to go around each LED and photocell. Sort of looks like a traffic light now. We are gonna replace the cardboard with thin plastic so it will look better. Anything else? Hmm, I don't now what the maximum length of the serial cable is, but we haven't had any problem with that. The PC is about 4 feet away from the track. I would guess that there is some sort of limit. One of the guys here just made a modification...he lined each hole were the LED's are, with aluminum foil. He said it will help reflect more light to the photocells. Just becareful that no foil touches the LED leads. Hmm, let's see if this causes our tower to catch fire ;-)

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