This electronic sensor system is for use with a computer tracking software such as Grand Prix Race Manager (GPRM) by Randy Lisano. My research found this to be the best software for the job and one of the best prices. It makes races run faster and more organized, this makes it more fun.

These plans are for a very inexpensive parallel port sensor system. (average cost $40-80 depending on supplier, Yes prices do vary that much) Originally based on plans from Cub Scout Pack 471's three lane version and modified for 4 lanes with the addition of features available for use with GPRM software and shown on the Grand Prix Race Central site.

I have previously built them into the base of the track itself and many people build them into the finish line over the track. I chose to build my electronics into a project box this time for maximum flexibility and ease of storage. The nice thing about this design of the circuit is it allows you to keep the Circuit box near the computer. Meaning the only long cable you might need is a very easy to find and relatively inexpensive one, a Cat 5 cable. It is peanuts compared to a long serial or parallel cable.

When faced with building another system and track I chose to make some changes in the electronics. These changes simplify the circuit, in my experience the start switch worked better without the comparator so I reworked the circuit and was able to eliminate one of the chips and the related parts, less components means less soldering.

For the electronic savvy the following will do. There are some pictures below also.
The Schematic
The Co-ordinates this also contains a material list in a chart.
This system can also support the Solenoid Start Gate.
I don't have step by step for this yet but I have made a schematic for it. Click here.

For an Overview/glossary of components OVERVIEW and a material list explanation.

Laying out the Circuit

The hardest part about building this circuit is figuring out how to lay the components out onto a circuit board without having a mess of wires and being able to fit it all onto the board. Here, the hard part is done for you! The photos below show you one way that you can lay out the components onto a Circuit board. This particular circuit board was chosen because Radio Shack also carries a bread board with the exact same layout. So you can test it out first on the breadboard then transfer it straight over to the circuit board.
NOTE: If you don't build the circuit on a breadboard first, be extra careful to get the parts in the right place. The board layout guide will have a table of board coordinates for each of these components as well as which lane they go to. In the photos below, the top strip (X) of the circuit board is used for the +5V power to the components and the bottom row (Y) is the ground.

Due to the difficulty in finding this printed Circuit Board, only available at Radio Shack, I will be reworking the circuit to use a standard perf board found at any electronics supply, Stay tuned. At this time you can still find it if you call around.

Construct the +5V Power Supply
(All testing is optional but keeps mistakes from driving you mad later)

Assemble the Components - Place the components onto the breadboard, as shown below, but don't trim the excess wire off of the components just yet. If you chose to use indicator LED's, make sure to wire them in correctly. The short leg (cathode) is wired to ground. Next, attach the wires to your power jack and temporarily wire it to the breadboard. Wire the jack so that the negative part of the plug is the ground (goes to the Y strip), and positive connects to the input terminal of the voltage regulator.
Caution: The two electrolytic capacitors need to be wired in correctly otherwise they may blow up. The negative terminal should be wired to ground.
Test the Power Supply Input Voltage - Now plug in your 6 to 18VDC power source. (NOTE: the lower the voltage the less heat produced, 9V is common and works well) Check your voltage regulator temperature first. If it is hot, disconnect the power supply immediately, and check for solder joints that have excess solder that is touching other solder joints or a neighboring copper foil trace. If you have the circuit wired properly and you chose to include an indicator LED, then the LED should be lit brightly. If it isn't, double check your wiring and the orientation of the capacitors (the arrows should point towards ground). Also double check that the LED is not wired in reverse. If you didn't install an indicator LED, then with a multi meter, check the voltage of the input pin of the voltage regulator to ground. You should get a voltage of greater than 5V.
Test the Power Supply Output Voltage - With a multi meter, check the voltage of the output pin of the voltage regulator to ground. This should be a constant 5V. If not, check your wiring and the orientation of the capacitors (again, the arrows should point towards ground). If the voltage cycles then the voltage regulator is bad and needs to be replaced.
Note: The non can shape capacitor doesn't have a particular direction that it needs to be installed.

Transfer the Components to the Circuit Board - Carefully transfer each component to the circuit board one at a time, solder in place and then trim the leads to length.

Note: If you need some tips on soldering, you can refer to The Basic Soldering Guide site.
Note: You may want to use a heat sink to protect the voltage regulator from getting overheated during soldering.
Soldering Tip: You can bend the leads slightly to hold the components in place until you are done soldering them, or use some masking tape on the front of the board.
Final Power Supply Test - Test the power supply out, just as you did before. If it doesn't work, double check all your solder joints and your wiring of components.

Construct the Lane and Start Sensor Electronics

Assemble the Components - The layout is for a four lane system, but it can be easily scaled down to fewer lanes. Double check the pin assignments for your Quad Comparators, since they may differ by manufacturer, most are the same, but not all. If they are not, this layout may need to be modified using the schematic as a guide. At this time, you do not need to wire in the photo transistors, IR LED's or the optional indicator LED's.

Test the Quad Comparator Outputs - Before you proceed, you need to study the pin assignments for the quad comparator and note the input pins for each lane/start signal and each output pin. To test each comparator output, one at a time, take a small length of wire and connect from the lane/start input of the quad comparator (pins 4, 6, 8, and 10) to ground. Then with a multi meter, or an LED for that matter, test across the wire terminal that correspond to that lane's output. If all is well, the LED should light up, or the multi meter should show close to 5V. Repeat this for all other lane/start signals.

Transfer the Components to the Circuit Board - Carefully transfer each component to the circuit board one at a time, double check all placements before soldering in place, and then trim the leads to length.
Final Test of the Circuit Board - Repeat the testing as before.

Housing the Electronics

Last time I used a standard project box from radio shack and mounted all main components and remote mounted the IR LED's and Photo transistors Make sure the box is big enough if you don't want to cut the board down to size as I did. The more room you have the easier it is to work on the circuit and the neater it will be. So this time I made a box from Plexi glass (see below). You could even use a plastic container from the dollar store.

IR LED Mounting- You need to build a frame to suspend the IR LED's over the track lanes.
I prefer the aluminum bridge for it's low profile and strength and ease of use, but it can be made of wood.

ALUMINIUM: Use 3/4 inch Channel Top and Bottom and 3/4 inch SquareTube for the uprights.
These pieces can be found at you local Home Depot or Lowe's etc. You will need extra LED mounts for this option and your holes will have to be the right size for the mounts you choose. Or glue them in place with silicone or hot glue. Sections of aluminium are bolted together using 8-32 machine screws and nuts.
Pictures of the Aluminium Sensor "Bridge".

Next attach the resistors and wires to the LED leads and use heat-shrink tube or tape to cover the connections to prevent shorting.. Connect the IR LED's with the short lead (cathode) wired to ground. Two Wires one for +5V, one for ground.

Photo transistor. Mounting - You can mount the photo transistors just as you did the IR LED's. It is actually a good idea to stack the wood or aluminium channel used for the IR LED's and the Photo transistors together and then drill the holes through both pieces at once. This way the holes will line up properly, but care should be taken to drill the holes perpendicular to the material. Use a drill press or a drill with a built-in level, if you can. Insert the photo transistors, attach the wires to the leads and add heat-shrink tube or electrical tape. Wire the photo transistors with the long lead (emitter) to ground (you should use one common ground for all four, five wires in all). Depending on your track design, you may want to attach the cable jack to the upright or to the side of the track. Now with the track, drill holes in each lane at the finish line, a bit larger than the holes in the "bridge" and then attach guides to hold the sensor frame in place.

Housing the Circuit Boards

Important Note: I have incorporated the future use of a solenoid activated start gate in both models pictured below and/or the start light tree(DB9 connector)on the black one. The switch on the circuit board is to switch pins in the event that I change from a start switch to the solenoid using the same wiring, (you may use a jumper instead if you do not want the flexibility), see Layout coordinates page for details.

External Connections - Drill holes in the side panel, to mount connectors for the external components (eg. power jack, parallel port etc.) Also, drill holes for the indicator LED, and secure in place if remote mounting them. Connect the wires to their corresponding locations on the circuit board. On my latest unit I mounted the LED's on the circuit board and made the box out of plexi glass.

Mount the stand-offs to the back panel, so the circuit boards will be centered in the enclosure, and then mount the circuit boards to the stand-offs.

Attach the Front Panel - Use screws to attach cover, do not glue together incase you need to access the system if there is a problem in the future. In the case of the plexi glass you can also use silicone, as it is easily cut.

Start Switch
Almost any switch will do. Originally I used a commercial momentary push button (found at any electrical supply, and some Home Depot's) mounted on a small 2 inch angle. I felt that because I was having the start gate land on the switch a small cheap switch just wouldn't do. Also it is only 5VDC so I did not enclose it. My newest switch is a magnetic switch similar to one found in an alarm system, but has N.C. contacts that open when the magnet is brought close to it. Depending on what switch you use you may need to change the mount. (see Overview/glossary for details) Attach a wire to the switch with a standard 1/8" phone plug on the other end (or what ever connector you use) to plug into the system.

Connect the Sensor Unit to the Track

This can be done in many ways, but whichever way that you choose, it should allow you to easily remove the sensor system from the track for storage. (see pictures of sensor bridge)

Final System Test!

Off-line System Test - Plug the photo transistors, start switch and power source in and conduct a final test. Block each sensor and activate the start switch and check the indicator LED's. If the indicator LED's do not change when activated, double check the wiring of the photo transistors, IR LED's and indicator LED's. It is very easy to wire these in the wrong direction. Also, double check all your wire connections to make sure they are snug and attached to the correct terminal.

Computer Interface Test

Connect a parallel cable from the unit to your computer and test the signals for each lane and start switch. You can use the Grand Prix Race Manager software for this, or some other software that is capable of communicating with the parallel port. If you get no communication between the sensor system and the computer, but the indicating LED's are showing that the sensors are working properly, then check the cable that you are using. You may have a "direct connect" cable that is meant for hooking two computers together. This type of cable will not work with the sensor system. If the cable isn't labeled, you can check it with a multi meter If you check the resistance from one end to the other on each pin (pin 1 to pin 1, pin 2 to pin 2, etc.) and don't get zero resistance, then you have the wrong type of cable. If this is not your problem, then check your wiring to your connector. You should also check your software to make sure that you are using the correct parallel port.

Any questions I might be able to answer, feel free to send a message to Dave

Clicking on the pictures of the circuit below will open a large version.

1. Power regulator section close up.
2. Main Circuit board without the sensor or output connectors.
3. Circuit board with input wiring.
4. Finished circuit with all the wiring.
(including the optional resistors and LED's mounted right on the board)

My first time using a project Box from different angles. The new one is slightly different.

Click these two for larger version.

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