arduino speedometer

[longhairedboy]

I just ordered some parts from Amazon (arduino uno r3, 7 segment 4 digit blue LED display, a plastic box for the arduino, a reed switch, pack of tiny magnets, and some resistors) so i can build a speedometer for my electric longboard. I'm doing this because its really fast and hella fun but i have only a vague concept for speed it seems. So while i know i'm probably doing north of 20mph without even squeezing the trigger all the way, which is still kinda scary after months of riding regularly, it would be nice to actually see how fast i'm going on a digital display on my deck.

My plan is to get RPMs directly from the wheels by embedding a tiny magnet in the wheel itself and placing the reed switch on top of the truck hanger so as not to bee too close to the road. Then I can wire that into the arduino and embed the digits display in the nose of the deck with some clever dremmeling, possibly covering the display with either lexan or epoxy or something. I can get Mph or kph pretty easily by doing some math in the arduino, since i have RPMs and the exact height of my wheels (83mm flywheels!)

I was wondering if anyone here has done this or something similar. How did it turn out? Got pics? I'd love to see them. There is something i found on instructables( http://www.instructables.com/id/Arduino-Skateboard-Speedometer/ ), but it uses a 1602 type display, which for me would be too hard to read without bending down.

 

[okp]

great ! you may also want to use the accelerometer of the adafruit flora sensor

 

[longhairedboy]

great ! you may also want to use the accelerometer of the adafruit flora sensor

http://www.adafruit.com/products/1247

it also has a compass! The accelerometer would be a cool thing to have on there though. Acceleration would be an awesome thing to keep track of. I was also thinking of eventually adding sensors to the main battery leads so i could see what kind of power is flowing through there when i'm on it and hit the trigger hard.

 

[okp]

yes, I gave up. I wanted the neopixel led to react according to the accelerometer; e.g green, then when accelerating it switches progressively to RED or another color

got too many variables to deal with. I am now running a rainbow sequence.

 

[777arc]

It would be a million times easier to just get the GPS shield for arduino and use GPS to find your speed. Assuming you are outside, it will be an incredibly accurate speed.

 

[longhairedboy]

It would be a million times easier to just get the GPS shield for arduino and use GPS to find your speed. Assuming you are outside, it will be an incredibly accurate speed.

I don't mind doing things the hard way to get the results I want. One reason I don't want to use GPS is because in the past i've tried a number of devices to get my speed on my push board, including phones, garmins, and gps based bike computers, and have had very sketchy results. By sketchy, i don't mean terribly inaccurate, per se, but rather an experience that just didn't feel real time in some way, so i decided to go this route to get a more 'dashboard' feeling speedometer. Also, GPS will likely be a battery drain compared to running a tiny current through a reed switch only when it clicks closed. This system should last me several months on a single nine-volt battery. Not to mention this also gives me RPMs, something i wouldn't be able to get from GPS.

One thing i didn't think about until some time last night was the life expectancy of the reed switch. It's going to be clicking pretty damned fast, not at all like the door and window sensors they're typically used in. Also vibration is likely going to be an issue, so mounting and placement is very important. I haven't decided yet whether to come up with a solution for the non-drive wheels or integrate it with the drive system in such a way as to not have to drill into the urethane to place the magnet. I could just as easily drill into the drive pully to place the magnet and mount the reed switch on the top-back of the motor mounts. That has the advantage of not damaging or unbalancing my wheels.

 

[mauimart]

Use a hall sensor instead of a reed switch. I have created Arduino based speedometers and tachometers. For the tachometers I simply mount a hall sensor outside of the outrunner can. You could just as easily mount a magnet to your wheel and have the hall sensor pick up on that. In the video below you should be able to see the single hall sensor off to the left for the rpm signal. The other 3 halls on the right are used for motor controller phase timing.

https://www.youtube.com/watch?v=OL4XvbuKoYk

https://www.youtube.com/watch?v=B6vtIfTjB_s
[youtube]OL4XvbuKoYk[/youtube]

[youtube]B6vtIfTjB_s[/youtube]

 

[longhairedboy]

@mauimart Thanks for the info! This is very helpful and I'm definitely going to look into this. I've never worked with hall sensors before but it seems like they would be a much better fit given what they're used for inside the motor. the reed switch idea seemed like a good one at first but the more i think about it, i doubt it could handle the abuse i regularly give this longboard. I run it like a dog every weekend on the bike trails and during the week i subject it to some of the worst paved roads Florida has to offer: my neighborhood streets.

I'll update this post once i get all the parts in and get it working.

I'm also planning on switching to an arduino micro pro once i get the prototype working so that i can fit the entire package inside the box alongside the battery and esc as there is no room for anything bigger than that in there.