Slot Car Track Power Control via the Computer's Parallel Port.
The Call Switch!
The following information deals with controlling the power to a slot car track using software, momentary switches, computer's parallel port and relays. Not all software that does laptiming and features track call switch support functions as advertised, for instance Laptimer 2000 has a check box for "Track Call Switch" (CS) in the options but I have not been able to get this feature to work. I e-mailed Gregory to get the proper wiring for the CS and he replied with pin #15 to ground (pin #25). I have tried this without any luck on several computers. Laptimer 2000 does control the power relay properly when operated from the computer, if you press the pause button the power is cut and the timer is paused. Gregory informed me he is working on a fix!
Mario van Ginneken the author of SRM, is now looking into incorporating this feature into his software and I hope it is included in version 2.30. However with the current version 2.20a only the power control works with the keyboard's ESC key when you pause a race. However there is a bug in 2.20a that does not stop the clock during a pause, this is fixed in version 2.30. Mario has been great and has responded to all my e-mails, his latest e-mail (June 21 2004) assures me this feature will be in the next version if all it takes is monitoring pin #15 of the parallel port. Thanks Mario!!
I was not able to test the DOS version of TrakMate because it uses the COM ports to control track functions and I did not bother to make the cables required to test.
PC Lap Counter may work as advertised but I find the software difficult to configure, I even had to write the author, Guy Langenakens just to configure my sensors to work with this software. In all fairness I did spend 20 minutes trying to get the power relays to work on pin #2 and the call switch to work on pin #15. I may e-mail the Guy again for help.
Out of all the software that I tested the only one that worked properly was Slottrak and I find myself drawn to this software not only because it works as advertised but the configurability of this software is amazing. It is windows only which will reduce its target group but if you have a Pentium 300Mhz CPU  or greater and you need  feature rich windows based laptiming software please consider Slottrak as a good purchase. The author, Tom has been a very good source of support and responds to e-mails in a timely fashion.
 
Click for larger image Click for larger image
The above schematic utilizes five SPDT relays to control track power. One relay per power supply per lane and one control relay*, if you only have one power supply then just use two relays.
The reason I really like this circuit is because the relays stay off while racing or practicing and they get energized when the pause function is activated. This saves wear and tear on the relays because having the relays energized the whole time you are racing or practicing causes the relay's coil to heat up and possibly burn-out if you do not use the expensive continuous-use relays.
*Please notice RLY1 is just a control relay for RLY2-5, I do this to minimize the current load on Q2.
I use surplus 12vdc automotive relays and an old computer power supply but an 12vdc AC adaptor would work just as well. 		This schematic shows a simple wiring diagram for your call switches. After many hours of digging Steve (sbs56 on SCI) came up with some very good quality switches that fit the bill perfectly. They can be found HERE. 
As well please search eBay for these switches as many vendors are selling on eBay for cheaper than buying directly from Happ. Please do not confuse the pins needed for operation, the schematic shows pin 15 however other status pins could be used but please never connect a data-line pins 2 through 9 to ground. If this happens you will be looking for a new parallel port pretty quick.
SensorTrak owners what does this mean to you! All of the people that have purchased my SensorTrak will be able to purchase a complete setup from me. I have used 2 different types of DB25 male ends, "solder lug type" and "crimp connector type". You can tell which type you have easily, the crimp type will have 3 wires sticking out of the connector and a legend written on the plug. Users of this type can install a connector directly on these wires. Users of the "solder lug type" will have to open up the cover-shell and solder wires on pins 2, 15 and 24. Some of the cover-shells are a solid construction but will slide off when the two screws are removed.
For others that are using a computer but either bought or made your own sensors you can also purchase a Track Power Control Box. The hookup to the computer will be the only thing different than with users that have my SensorTrak.
What is included.
Project box with all electronics mounted inside.
AC Adaptor, European users get a small 220VAC computer power supply.
Push buttons can be included or you can order them directly.
The project box will have a number of external connections for lane power, computer hookup and power hook up.
I have not come up with a total price yet but I will have something soon.
If you are interested please e-mail me.
Pictures of a completed Track Power Control Box. (TPCB)
Click on image for larger view.
The completed TPCB showing the inputs and outputs.
When on the red LED indicates main power after the fuse.
When on the amber LED indicates the controller relay is energized and when on the four green LEDs indicate the lane control relays are energized.
This picture and the one below it shows the internal wiring of the TPCB. This one uses five relays, one relay to control the four lane/power supply relays. This version is probably the most complicated because of the four independent power supplies used by this person. Most people have just one or two power supplies which would make the  relay count go down and if only one power supply was used then we would only need one relay.
 
This is a shot of the main power switch and fuse holder.
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Disclaimer: Use this information at your own risk. I will not be held responsible for misuse of these instructions.
DO NOT attempt to this project if you do not understand DC polarity, serious injury could result if reversed polarities occur.