Scratch Built HO Scale Odometer Cars for measuring distance along right-of way make for an interesting and useful project. 
Built for the North River Railway, Owned by Bob Van Cleef

 

 

Measure your right of way with this

ODOMETER CAR

 

 

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Have you ever wondered exactly how long your mainline is?  Or have you given a thought as to how far a car travels during an operating session?  There is one way to find out.  Build an odometer car that measures distances.

 

This project makes a nice conversation piece and with modern components the circuitry is not that hard to build.

 

This model railroad Odometer car can be used to measure the length of your right-of-way or to measure how far a car can travel in an operating session.  This car was built in HO scale but could also be built in S, O, G or any other scale

 

 

Here are two variations.  The first variation is embedded into a flat car.  This configuration has a lower profile and center of gravity, which in turn gives it a more plausible appearance.

 

 

The second variation is a “drop-in” portable unit that simply rests on a flat or gondola show here.  The only modifications required for the car is a small hole in the bottom over one axle and a special truck.

 

Both cars have the same electronics, operate the same way and are equally as accurate.

 

 

 

 

This "drop-in" protable load is designed to give any HO train car the ability to measure distance with a mimimum of modifications.  A small viewport had to be cut in the floor and a modified truck swaped with the original and the car is ready to go.

 

Distance is determined by counting the revolutions of an axle using an infrared light emitting diode and a photo detector.  Both point to a specially modified axle of a truck.

 

Almost any truck can be modified for this purpose.  Simply glue and wind a ˝” strip of paper around an axle to form a drum about 9/32 in diameter.  The exact diameter is not critical.  paint one half of the drum black and the other half white or silver as shown

 

 

There are a number of counters suitable for this project. Some have up to eight digits and others have digits of different heights not to mention many other features.  There are also several configurations available.

 

I used a Red Lion “SUB-CUB 1” which is designed to “snap in” to a PC board.  It is rugged, easy to understand and one coin battery can keep the display active for a long, long time.

 

The Red Lion Sub-Cub 1 can be obtained for as little as $15.oo and is rugged enough to hit the floor and still work.  It can mounted on the top of a model train car for high visibility or a more expensive and smaller cousin can be hidden inside a passenger car and read through the windows.

An evaluation board can be useful for learning how to work with this type of component.  The pins are arranged for use with a SIP socket or any of many prototyping boards

This evaluation board is available to test and learn about both the SUB-CUB1 and the SUB-CUB 2.  It can be cut and used as a daughter board for your project, or you use it as a template to lay out your soldering traces.  This module is a bit unusual as you will not see any individual pins.  There is a conductive ‘zebra’ strip at each end to make the required connections against bare copper conductive pads on a printed circuit board.  There is no direct soldering.

 

 

The specifications sheet for the counter includes a dimensional layout of the mounting holes and the pads required to make electrical contact.  Here a 1/16” single copper clad pc board is used and the separations between the pads are hand filed.  It worked just fine.

 

The “leads” from the pads are soldered using regular solder and the counter is snapped into place later.  Wiring connections on the other side are made with a Low-temp silver-based solder.

Printed circuit boards for model train odometer car counter.

short lengths of brass tubing holds the LEDs in place in position
Almost any model train car can be converted into an odometer

  

This represents the bottom of the car.  Two holes are drilled for the Ľ” tubing used to hold the emitter/detectors in place.  Be sure to remove any sharp edges and smooth the inside of the tubing.  Note the pads witch will separate The perf board from the base with just enough clearance that the wiring connections are not crushed

       

 

This is the top view of the electronics.  The leads of the LEDs extend past the board and allow for a small amount of adjustment of how close they are to the axle drum.

This is the circuit that can be mounted in any train car. 
Use a low-temp sold for the leads of the LEDs for best results

This is an example of how the odometer circuits can be embedded into a flat car for a low profile.  The main battery in sunk deeply in the thickest part of the center to hide if from view.

  

This view shows how everything is arranged inside the box loaded flat car.   The counter is in the center with the reset button to the right and the main power on/off- switch to the left. 

 

Below is the 3v coin battery to the left, a 9v rechargeable battery in the center, and the circuit board to the right.  The three views below show the underside of the car.

      

 

 

The slightly larger portable or stand-alone version has the same parts with a slightly different arrangement. 

 

The three views below show a gondola modified for use with the portable odometer configured as a load.  Note the relationship of the view port and the axle-mounted drum.

 

 

 

  

Wiring schematic for the North River Railway Odometer Cars      

      

      Odometer Scematic

  

(B1) is a 9v rechargeable battery and powers the circuits that deliver a counting pulse to the counter.

(L1) is an infra-red light emitting diode that will illuminate the axle drum as the car travels along.

(R1) Will limit the current to the very small amount of 0.003 amps to keep the drain on the battery as small as possible.

(L2)  is the infra-red detector that changes resistance with the amount of light it receives.

(R2) is a fixed resistor that develops a voltage swing from about .3 volts to 7.5 volts under ideal conditions as the drum turns This is much more than is required to trigger the counter.  Unfortunately, you will find that when everything is assembled this voltage change may be much less due to less than optimum conditions.

C1 is a capacitor to prevent sudden and spurious changes of this voltage that may cause false counts.

R3 is a resister that prevents overloading of IC1 input while allowing slight changes in feedback at this input.

R6, R7 and IC1 serve only to improve the reliability of this circuit especially as the main battery begins to wear down.  R6 makes it harder to turn IC1 “ON” and once “ON” it is harder to turn it "Off.”  R7 sets the point at which the on/off occurs and IC1 amplifies the voltage changes it receives at it input so that it is either at 0v or close to 7.5v or the full battery voltage.  This circuit would work without these three components under ideal conditions but the mechanical positioning becomes much more critical for reliable operation.

R4 and R5 divide the voltage of the pulse signals to the counter in half so that it is lower than that which might damage the counter.

IC2 is the counter itself and requires only a tiny amount of power to display its current value so the coin battery (B2) is sufficient to keep it active for a long time.

R8 is required by the counter as part of the circuits to drive the LCD display

R9, R10 and C2 work in tandem to “gently” drop the voltage to the reset pin when clearing the count and then to allow the voltage to slowly return to high and allow counting

 

  

PARTS LIST*

PART

DIGIKEY #

Description

Use

B1

N705-ND

9v NiMH rechargeable battery

Main power

B2

SY189-ND

3v Battery, Panasonic  CR2032

Counter display

C1

399-4208-ND

.01 µfd  (103) capacitor

Low pass filter

C2

399-4189-ND

.047 µfd (473) capacitor

Delay

IC1

LM358ANFS-ND

LM358 Dual Op AMP

Operational Amplifier

IC2

RLC1000-ND

Red Lion SUB-CUB   1  SCUB1000 

Counter Module

L1

160-1028-ND

LED 50ma infrared emitter T1  940nm

Detect drum rotation

L2

160-1030-ND

LED infrared receptor

Detect drum rotation

R1

1.50KEBK

1.5K, 1/8w resister

Current limit

R2

100KEBK-ND

100K 1/8w resister

Voltage Pull-up

R3

100KEBK-ND

100K 1/8w resister

Current limit

R4

1.0MEBK

1.0M 1/8w resister

Voltage Divider

R5

1.0MEBK

1.0M 1/8w resister

Voltage Divider

R6

2.7MEBK

2.7M

feedback

R7

U262R504B-ND

500K potentiometer  brown

Threshold voltage

R8

2.4MEBK

2.4M

Required for display

R9

1.0MEBK

1.0M

Reset current limiter

R10

1.0MEBK

1.0M

Reset recover

SW1

EG1901-ND

Switch

Main Power on/off

SW2

EG1023-ND

Tact SPST push button

reset

 

V1004-ND

Vector keyboard .1 x .1 hole pattern

Circuit board

 

A24807-ND

8-pin Socket

Used for IC1

 

473-1000-ND

Single clad copper PC board

Used for IC2

 

BH800S-ND

Battery clip for coin battery

Used for B2

 

*All parts listed are available from:

DigiKey Corporation   http://www.Digikey.com
701 Brooks Avenue South, Thief River Falls, MN 56701 USA
Phone: 1-800-344-4539 or 218-681-6674 or Fax: 218-681-3380

Digikey provides pictures and spec sheets on request or they can be downloaded from their site.

  

 

 

 

A few rough calculations to determine distance

 

Diameter of typical freight car = 33”

Circumference of wheel = (33”  x  3.1416)  = 103.6”

Distance / 10 revolutions =   103.6 x 10 = 1036”

Revolutions / mile =  (5280’ /  1mi)   x  (12” / 1’) x  1 revolution / 103.6”  =  611 revolutions / mile

If a scale mile (smile) is 1/6 of a mile

Then  6 smiles equals to 1 mile

And  100 revolutions of wheel = 1.00 on counter = 1 smile    (or 1/6 scale mile)

 

In HO scale a Smile would be equal to 5280’ / 87 HO scale  x  6 smiles / 1 mile = 10’

Each count on the counter would then be about 1 actual foot

999999 revolutions = 103672454 inches =  6639371.157 feet = 1636.2 HO scale miles 

In the real world this would be 18 actual miles

 

A train traveling at 10 smiles / minute (10 feet)  would be traveling at 60 miles per hour

Train crews should be encouraged to run their trains very slowly.

 

  

 

SUB-CUB Pin assignments

 

 

   

    

 

 

 

 

 

SUB-CUB Pinout

 

SUB-CUB Layout

 

LM358

     

LM358 Operational Amplifier

 

 

 

   

   

 

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Last update    7/26/2012