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Topic: Speedometer for 1/8 scale railroad (Read 2392 times) previous topic - next topic


Hello folks, this is a feasibility question for now, which may evolve into a more technical question later. I am in the process of building a 1/8 th scale locomotive, and want to be able to set up a speedometer that gets information from the rotations of the axle, not from GPS. I have already seen multiple posts here, so I know it is doable. I want to output the speed on a LCD screen, and be able to select different options, such as scale speed or true speed, or maybe even both. I'd like to be able to output it as either a number (nn.n) or a gauge (or two side by side).

If I can add a battery level meter (2 independent 24 v systems) and a cumulative hour meter that records when the drive motor is receiving power, that would be fantastic.

And if I can also pass a feed fromo a video camera through that same LCD, and be able to select a feed from either an IR or regular camera, then I might possibly jump over the moon.

If I am totally out there, let me know too. Any suggestions are appreciated.

Oh, on more thing, if there was a level of experience that was somewhere below knows absolutely nothing, that would be close to mine.


And if I can also pass a feed fromo a video camera through that same LCD, and be able to select a feed from either an IR or regular camera, then I might possibly jump over the moon.

No need to be lacing up your jump shoes, then.
The art of getting good answers lies in asking good questions.


The speedometer is feasible, rotary encoder is the magic word. displaying that (RPM) as well as the calculated speed and some voltage readings should be not problem either.

A bit more problematic is the camera feed on the same display. An Arduino is not made to transport that amount of data to displays (usually connected with some serial interface). It's probably easier to leave the video stuff separated from the measurement stuff (which is more the area of microcontrollers as the Arduino is).


Perhaps you did not notice yet that here  "LCD" usually refers to something like a 16x2 characters alphanumeric display.
It might display a bar graph in the second row, and it's also availabale in up to 20x4 size.
A minimalistic menu with up and down buttons is nice to display a lot of information, though.

Graphic LCD and touchscreen stuff uses it's own processor and external memory for images etc.
Can be connected (in general anything can be connected ;) but that's not too related to Arduino itself. 


Hi Guys, thanks for answers. I have a better understanding now. I realize that I was trying to be too complicated. A two line out put, that could have a header on the first line, and an output on the second line sounds pretty good. To select the different outputs (real speed, scale speed, odometer, hour meter) would it be best to use a push button to rotate through the displays, or a rotary switch? Also, can the LCD's be backlit, or night visible?

I read some about Reed systems for doing a speedometer, is that a good way, or is a rotary encoder better? How does a rotary encoder work for that matter? I was thinking two of four small magnets, mounted on the axle, and some kind of counter that counts the number of times the magnets pass, and converts that into a speed value.

Thanks for your feedback.


A rotary encoder (http://en.wikipedia.org/wiki/Rotary_encoder) is better suited if you wanna know not just the speed but also the direction. If speed is everything you need, reeds are better suited because they are more immune to dirt and the like (rotary encoders often use light for reading).

For getting the speed value usually it's better not to count the pulses but measure the time between two pulses. That way you get a value more frequently and have a higher resolution (typically).


Thanks Pylon for the clarification. I think reed is the way to go, since it is going to be part of a locomotive running in an outdoor, desert environment, so dust is big issue.


You can also use hall effect sensors, similar to reed switches but no mechanical parts and no switch bounce if you use one with inbuilt schmitt trigger.

Rob Gray aka the GRAYnomad www.robgray.com


ok, taking all the suggestions into account, what board would you recommend I start with, in order to have a two line LCD output, that uses either a rotary selector or a push button to cycle through various outputs with a header on the first line, and data on the second. For example:


Scale Speed


I would like to be able to capture and display two different speed values, two cumulative distance values, two trip distance values, and an hour meter (based on when a motor is turning).


Any Arduino will do that, 5-6 pins for the LCD and 1 for a button, 1 for the speed sensor.

Rob Gray aka the GRAYnomad www.robgray.com

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