The hardware, we had several versions made, the first one used several transistors, and was very unstable. The second one introduced the LM324 IC and used BPW photodiodes as sensors. It worked fine. The only problem with this version is that the right sensors are very hard to come by, unless you really want to spent money ;-) well we didn't.
The third version uses LDR's as sensors which are readily available at electronics stores ect.. For easy install in your track get the approx 5mm round versions. The resistance between dark and light need to be at least a copple of K, but we build in a Potentio meter of 100K (a multiple turns one is handy but not neseccary) which you can adjust to make it work with a lot of different LDR's Just experiment....... The following drawing is for 1 slot on your track so you need to build this twice, but offcourse you use the same LM324, powersupply. Put the LDR's on wires from the PCB to the track.
Drill 5 mm holes just beside the metal rails of the slot (preferable to the outside). Do this for both slots. Fit the LDR's into the holes. Build a bridge over your track to fit in the optional bright red led's. These must be placed right above the LDR's. You also need to get a male 25 pind SUB d type connector to connect to your parallel port.
The cable between the PCB and the Parallel port can be anything like UTP cable or something like that. Only 3 wires are used for now. I might be including a speed trap on the my straight which requires an additonal 2 wires to the parallel port, but i am not certain when i am going to implement it.
Considerations :
The max. lenght for the parallel cable should not exceed 2 meters
Preferable use twisted pair cable to your sensors
Make sure your track uses a clean power supply, there should almost
be no noise on the DC voltage.
To much noise/spikes on the track can cause the timing system to trigger!
The first slot uses on the LM324 :
PIN 3 = +
PIN 2 = -
OUTPUT PIN 1 to parallel port pin 13 (select)
The second slot uses on the LM324 :
PIN 5 = +
PIN 6 = -
OUTPUT PIN7 to parallel port pin 12 (paper end)
Offcourse the LM324 needs power :
PIN 4 = +5v
PIN 11 = - (GND)
You need to buy the resitors in the diagram. The ambient light could be sufficient to trigger the sensors, if problems are encountered put f.i. a very bright red led above the track pointing down on the LDR. This will make sure the the difference between light and dark are big. You can build al this stuff on an experiment PCB board and use wires to solder it al together. Be creative about it !!!! One more thing, if you are really stuck with building the hardware, email me, i will try to help you out. GOOD LUCK, Alex
P.S. I want to thank my friend Peter v/d Voort For his valuable input
on the hardware Visit his homepage on P.
vd Voort Elektronics he runs his own elektronics company !!!
Here is a Picture of my track with the sensors Installed. You can see
them between the two white
line in the middle. The part of the blue thing you see is the bridge
where the Bright red leds are mounted.
The track under the bridge is Plastic and the one connecting to that
are MDF wood with routed
slots. The below side i used copper tape, and the above i used Aluminium
tape.
Part List :
4 * 10 K resistor
2 * 100K potentiometer (PCB version), a 25 turns is handy but not required
2 * LDR, 5 mm rond version, metal case like transistor with transparent
top
The LDR's i used come from farnell
Farnell Components and have Order
number 179-611
Conrad Elektronics also have the right
components
Radio Shack should have them to
1 * LM324 IC, with 14 pins IC socket
1 * 5V DC power supply (small adaptor will do)
1 * Sub D 25 pin male parallel port connector
optional :
2 * 220 Ohm resistor
2 * Bright Red led (transparent 5 mm version is fine)
Picture of the LM324 IC :
Is your IC getting hot ? Click here
A doc. about soldering : Click here
There is some information about How the parallel port works and how
you can interface to it, here are some links to that information (i used
some stuff from this to design my hardware) : Parallel
port projects from their main page select tutorials.
Parallel port description
1998 Alex de Kloet
Most recent revision woensdag 23 november 1998