In this speedometer implementation the display remains in a fixed location or can be carried by the operator.

  The Speedometer uses an Aluratek Bluetooth transmitter and receiver pair to send the speed pulses to a CATEYE VELO 5 bicycle computer to provide a remote speed indication and an odometer, other models of computer should work but the ones that are wireless are not suitable as they have a very short range. All of these items are available from a number of commercial and on-line sources.

  The stated range of the transmitter and receiver is 33 feet which should be more than adequate for most layouts and even clubs.

  This implementation uses a bicycle trip computer and an adapter for a digital display, however, with a suitable app and a smartphone could also be used for the display but this is beyond the scope of this page and has already been done commercially.

  A LM2917N-ND - Frequency to Voltage Converter IC, can be used after the receiver to provide an analog DC output voltage that is directly proportional to the speed. This voltage could be used to control a throttle to make a form of cruise control and an analog milliammeter could be used as a speed indication. A dual voltage comparator and perhaps two optoisolators in a window configuration would be needed.

  Select the part number above and do a google search, chances are you'll get something. Make sure it is for the supplier you normally use.

  For the Transmitter and Receiver: Select ones that look like their images on the page. There are a number of different Aluratek products that will come up during the search. Pick one that will fit your particular project.

  Note that the block in the picture is not an ED1601-ND, it's an extra one that was available so I put it to use on this project. ( Any 5 mm or 3.5 mm block should work as long as there are 4 positions available. 2 Blocks of 2 Positions = 4 as shown.

  Something Relevant May Go Here In The Future.

  The adapter terminal block holds transistor that interfaces between the Bluetooth receiver and the Speedometer's display unit.

  The adapter terminal block takes the place of a reed switch that would normally be mounted on a fork for a bicycle installation and provides an input to the computer.

Model Railroad Speedometer Car Axle Magnet(s)

  NOTE: Two axle magnets are shown in the photo. Therefore, there will be two pulses per wheel revolution and the circumference is effectively halved. The bicycle computer can be set to a diameter of 33 inches or the circumference to 103.7" (8.89 feet) to compensate for this and the displayed distance and speed readout is automatically halved.   This is true for any scale as long as the wheel diameter is correct for that scale.

  Two axle magnets are used for low speed performance and accuracy. With one magnet the display might drop out at very low speed as these have a minimum input rate to keep them active. (Even though the speed indication may drop out, the odometer will continue to count the distance. An icon on the display will blink every time a pulse is received.)

  Notice that the bottom of the car has a huge hole in it, this was the result of a previous sensor that was much larger than the Hall-Effect sensor in this version of the Speedometer Car. Also, there is a PCB shim under the truck's bolster to maintain the correct coupler height.

  A 33 inch freight car wheel has a circumference of 8.64 feet. Which equals 611.1 revolutions per mile (5280 feet). (Or, 1222.2 pulses per mile for 2 magnets.)

  A 40 inch locomotive wheel has a circumference of 10.47 feet. Which equals 504.3 revolutions per mile (5280 feet). (Or, 1008.6 pulses per mile for 2 magnets.)

K&J Magnetics B821

1/2" Long x 1/8" Wide x 1/16" Thick

Magnets On Axle Diagram

  No Units are shown as it's all relative at this point, assuming the wheel is correctly scaled to 33 inches in diameter. The magnets are K&J Magnetics B821 - Nickel Plated - 1/2" Long x 1/8" Wide x 1/16" Thick (N42 Type).

Hold down the control key while clicking on the link, wait and then make the approprate selection - "new window or tab".

1. Divide the circumference by 12 to get feet. (103.672 Inches / 12 = 8.639 Feet) (8.64 Feet)

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2. Divide 5280 by the circumference (8.64 Feet) to find the number of revolutions and pulses per mile ( 611.1 ).

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3. For 1 Axle magnet - Set up the bicycle computer for a wheel circumference of 8.64 feet or 220 cm to find the number of pulses per mile. ( 611 )

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4. For 2 Axle magnets - Set up the bicycle computer for a wheel circumference of 4.32 feet or 110 cm to find the number of pulses per mile. ( 1222 )

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5. Power up the transmitter and receiver and allow them to sync.

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6. Place the car in a train and head out on the road.

Model Railroad Speedometer Car Computer Example (CATEYE Velo 5)

  The speedometer uses a bicycle computer to perform the speed and distance calculations and provide a real time display.

  Just about any bike computer will work, however, it should not too bulky so that it is easy to carry around. If the computer remains in its bike cradle, which provides the connections to the computer module, it could be put back on a bicycle quite easily for normal riding use.

  A wrist band or a small box could carry the receiver, adapter block, and a computer. Or, a small box that fits in a pocket with the display attached to it so that the display could be placed in an easy to see location such as a control panel or held in the hand for walk-around use.

  The adapter circuit consisting of an NPN transistor and a resistor was constructed with a 4 position terminal block made with 2 position 5 mm blocks. Other sized blocks or as small pcb can be used as long as there are 4 positions to work with.

Aluratek ABT01FTx Transmitter

  The ABT01FTx Transmitter and AIS01FRx Receiver are each supplied with a USB charging cable and instructions.

Aluratek AIS01FRx Receiver.

1.   The example shown is a CATEYE VELO 5 but many other models should work. It's best if they have an actual reed switch in the pickup head.

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2.   This car uses a 9 Volt transistor radio battery (B1) but the power consumption is very low. A good source of batteries is to save the old ones from the annual smoke detector battery change and reuse them in this project. There's still plenty of life left in them for the speedometer's needs.

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3.   Initially, the plan was to use the battery in the transmitter to power the oscillator but there must be a diode at the power input to the transmitter.

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4.  

PCB No. 1 Model Railroad Speedometer Circuit Board - Detector And Oscillator Circuit Board - Digikey number SBB1002-1-ND

PCBs 1 and 2 Model Railroad Speedometer Circuit Boards

PCBs 2 and 1 Model Railroad Speedometer Circuit Boards

  This board has an Digikey LM358P dual OPAMP that is used as an oscillator and comparator as well as the Digikey J211-D74Z FET used as a gate that sends a signal to the transmitter.

  This board is powered by a 9 Volt battery. The ( Digikey 36-232-ND ) connector for the battery can also be seen in the photo.

  Also visible is a 1/8^th inch stereo audio jack that connects the oscillator to the transmitter. Only one channel is connected although some other information could be sent with the other channel although I don't know what that would be.

1994 Model Railroad Speedometer Car - PCB is Digikey number SBB1002-1-ND

  The SBB1002 board was used to build the detector and oscillator circuit board that rides in the gondola.

  The circuit below uses an LM2917N-ND Frequency to Voltage IC to convert the pulses from the Speedometer car into a DC voltage. This allows a low current, analog milliammeter to be used as a speed display.

Model Railroad Speedometer Frequency To Voltage Converter Schematic

  This voltage could be used to control the output of a throttle to adjust the output voltage to control the speed.

  No signal conditioning would be needed to drive the circuit the Interface unit would suffice to change the oscillating signal from the speedometer into pulses for the LM2917N-ND.

  The LM2917N-ND is not particularly easy to use and requires careful selection of the component values for good results. Follow the information in the data sheet carefully.

  The next diagram is for a speedometer that was developed in 1994 for the LMRG.

  This circuit worked in O Scale but could not be reduced to use for HO Scale because of the actual components used. The Transmitter was very large, it would only fit in an O Scale gondola. The odometer display is the one used for the 1994 Odometer car article in Model Railroader Magazine. It reads up to 140MPH but I don't recommend doing this on a layout.

  This TMXxxx units shown on the diagram will fit in an HO scale car but are not exactly easy to use although they seemed to work fine.

1994 Model Railroad Speedometer Car Schematic

  The next photo is for an early Speedometer and Odometer display that was developed for the LMRG. It is from an old laboratory pH meter and has a built in odometer. The same odometer display as used in the 1994 Odometer car Model Railroader article.

O Scale Model Railroad Speedometer Car And Display

1994 Model Railroad Odometer Car And Display