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How To Build An Interface Board For A SRT Lap Counter System

The SRT (Slot racing Technology) guys make a great functioning & very versatile lap counting system that can be used with a club or commercial style slot racing track.  It is also very reasonably priced and can be used with any HO, 1/32 or 1/24 scale 4, 6 or 8 lane track.  I have used their system for a number of years & recommend it highly.

Recently one of our basement club racing guys bought a system for use on his 8 lane basement track.  To help make  the installation of this package simpler I offered to sort out all of the electrical schematics and build an interface.  This interface board allows very simple connections to the lap counter, track power and cheapo computer where the software resides.

To start the project I took a trip to the local Home Depot and rummaged through their bin full of scrap coming up with a very nice Formica covered section of particle board ... & it is hard to beat the price !  A 1.4 amp 15 DC volt power supply that was salvaged from a defunct paper shredder was pressed into service ( I knew I would use it one day !).  The one tip I would suggest with the SRT system ... use an independent power source (like this) to run the system that is a direct AC plug-in .... this gives you the flexibility to have the system still function well even if you turn down the main power system to have some kido's racing ... this big "wall pack" unit provides plenty of power in this case since we will be using only one relay on the power ground side (to turn the track on and off - in this case all 8 lanes at once), but a more substantial supply would be needed if many relays were activated such as in a commercial track setting ...

One technical tip for construction is to solder each & every connection (with the exception of the terminal strip screws) using a good grade of 60/40 rosin core solder.  As always with any electrical project, never use acid flux or acid core solder ... it eats copper wires for lunch !  All of the wire connections that were soldered were also covered in heat shrink tubing, simple and cheap to do, but makes everything look sharp and is more robust against stray electrons !  Double stick RC servo tape was used to mount the power supply & the plastic tie wraps were added as insurance.  Labels were produced with my CAD software, but MS Word would also work for this, the labels were printed on sticky back Avery label sheets and covered with clear contact paper.  The label was even made oversize so part of it sits under the screwed on terminal strip so there is no chance that the label is going to fall off .. at least not in this century ....

Some cable ties were screwed to the base to provide strain relief to the main cables that go to the DB37 connector in the back of the computer (attaching to the SRT timing card).  The only "exotic" touch I used in the assembly was to use all-electronic self resetting circuit breakers in place of the 1/4 amp, 1 amp and 5 amp fuses that the schematic called for.  These components were placed on a small circuit board along with one of the diodes we use in our controllers.  This diode, used in this way, is what is called a "flyback" diode.  The purpose of a flyback diode is to dissipate the several hundred volt spike of energy that is created when an inductive device (in this case the relay coil) is turned off and the magnetic field around the device collapses.

Otherwise, there is no rocket science involved in this, just careful assembly & complete adherence to the very good directions and schematics that are provided by SRT.  For more information from SRT, their contact number is : (661) 944-6307 & the web site is : .

Hope these tips are are of interest ....

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