Model Railroad OdometerCar

Originally printed in Model Railroader Magazine

"Build a model railroad odometer car"

Model Railroad Odometer Car Photo (44k)

  This page features a photo and schematic from an article that was published in the August 1994 issue of Model Railroader Magazine. The article was titled "Build a model railroad odometer car".

  The Car shows the distance a train travels on a 5 digit LCD display. The distance is indicated down to 1/100th of a mile (about the length of a 50 foot car) with an accuracy of approximately plus 2 percent using a standard 33 inch freight car wheel.

  Simply stated, the Odometer Car counts the number of revolutions of one of the axles, divides it by six and displays the result on the counter module.

  If you are interested in or would like to build this device you may contact the MODEL RAILROADER Magazine customer sales and service department by e-mail at to order the back issue or a photocopy of the article when the issue is sold out.

  The photograph and schematic shown on this page are Copyright 1994 MODEL RAILROADER Magazine and used by permission.

Model Railroad Odometer Car Schematic

Odometer Parts List

COUNTER MODULE  -  Radio Shack part number  277-302 (see notes)
OM1  -  Infrared Emitter/Detector module
TIL 139 (see notes)
IC1a, IC1b  -  1/2 of LM393 Dual Comparator
IC2  -  MC4017B Decade Counter/Divider

R1  -  470 ohm 1/4-watt
R2, R5  -  470K ohm 1/4-watt
R3, R4, R6, R7  - 22K ohm 1/4-watt

C1, C2  -  0.1uF

Descriptions of the following components can be found in the text of the
original article.

S1  -  Magnetic reed switch

B1  -  3 to 4.5 Volt battery pack 
B2  -  1.5 Volt counter module battery

Miniature connector
Axle mounted drum
Circuit board
Small magnets 

Odometer Car Notes and Updates

  The following link is for a model railroad Speedometer/Odometer made from a trip odometer of the type used on bicycles.

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Please Read Before Using These Circuit Ideas

  The explanations for the circuits on these pages cannot hope to cover every situation on every layout. For this reason be prepared to do some experimenting to get the results you want. This is especially true of circuits such as the "Across Track Infrared Detection" circuits and any other circuit that relies on other than direct electronic inputs, such as switches.

  If you use any of these circuit ideas, ask your parts supplier for a copy of the manufacturers data sheets for any components that you have not used before. These sheets contain a wealth of data and circuit design information that no electronic or print article could approach and will save time and perhaps damage to the components themselves. These data sheets can often be found on the web site of the device manufacturers.

  Although the circuits are functional the pages are not meant to be full descriptions of each circuit but rather as guides for adapting them for use by others. If you have any questions or comments please send them to the email address on the Circuit Index page.

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