TOPIC: Detecting Wheel Rotation - Reflective Tape or Paint - Ideas?

Hey guys! Long time no see! I have a question...

I have an exercise bike I want to add electronics to. Somewhat simple stuff really, but I need advice about detecting revolutions of the flywheel, with moderate resolution.

I have IR Emitter/Detector pairs in various forms and makes, and I want to use it to count ticks on the flywheel. I do not want to add any significant weight to the wheel, so I thought about reflective paint or thin tape so I can generate some kind of digital signal as the "ticks" pass by the sensor. If I use this technique, I thought about varying the length of a few "frame" points so the signal varies depending on what point is read. Not necessarily a complex encoding pattern, just a unique one to the wheel for knowing where the full revolution point is, and maybe at every quarter for timing/syncing correction. This presents a little coding problem overall because as the wheel varies in speed, so do the lengths of each point reading. I realize I cannot use static duration to my expectations. I thought about printing a simple bar code for each point with a start/stop bit, and encoded data that can be read at any speed. Not sure yet.

So that leaves me wondering what reflective surface to use. Paint? Adhesive reflective surface? Just paper with a black and white code printed on it and stuck on with light glue?

I thought about using tiny magnets with a hall effect transistor also. Each magnet will have a different magnetic signature but I'm not sure how that would change based on the speed it passes by.

Any thoughts? I would love to hear them!!!!

For the curious... the 'electronics' I am referring to is just display readouts for speed, duration, caloric burn, and maybe some memory function that tracks progress. I will be using over-kill hardware of course (hop style lol), using a BeagleBone Black (loaded with Debian Linux), a touch screen HDMI 5", the sensor package, and wifi to tie it into my home server for populating a database. I will simplify it with more scaled down processing and input/display hardware when I get the software tweaked the way I like it. I have been away from the PIC series for quite sometime, but my new BeagleBone Black supported test bed will allow me to write and use tools to make use of my favorite beloved PIC line again.

Thanks you listening, and your time!

Hop

I dont understand why you want to know the position of the flywheel. Why not just a few strips evenly spaced, like the typical encoder, and just measure time between strips? Then you have RPM with a simple calculation.

Hmm, actually, good point lol. I guess I was worried about missing a tick, thinking redundancy. Not sure why. Thank you. What about my reflective surface question? Strips of what?

Optical sensors like this one from Elecrow could work well in this application. They have a working range from a few centimeters to about half a meter. You can probably find similar sensors on eBay or maybe even Tayda.

The best target for these is reflective tape; a great source is the reflective tape used on bicycles. Use a single piece if you just want to know RPM. If you really need wheel position, you might put a strip of tape every 90°, with two pieces separated by a small gap at one of the positions.

These sensors have an open drain output. Connect a load resistor between output and V+. When the sensor sees the tape, the output will go low.

In a previous life, we used sensors like this when balancing rotating equipment. A single piece of tape on the shaft or coupling provides a phase indication between the "high spot" and a known shaft position. A problem there was always getting the reflective tape to stay attached on a shaft that might be oily, wet or have steam blowing on it. It was not a happy day when the tape went flying half way through the procedure!

That is awesome guys, thank you! Jon, I'll try what sensors I have first, then use this if I need something better. Thank you!

I finished my BeagleBone Black prototyping tray today. Here is what I have in that tray... (straight from my facebook)...
the tray is a steel wire shelf-like unit that is designed to hang off my server rack on wheels. I just got wireless working with a static IP after having to compile an updated driver for the EW-7811Un 802.11n Wireless Adapter [Realtek RTL8188CUS]. Everything is working great! Now I can start work on writing code for sensors, etc, cross compiled in C++ and burned into more simpler devices. Big wins for me today! =)

Damnit. I missed clicking REPLY and hit DELETE instead and Hop's message was gone before I could blink. I am so sorry!

Reflective tape will work well with an optical sensor.. From personal experience, it will work reliably to 11,000 RPM, provided there are no steam leaks blowing directly against it and the shaft you're putting it on isn't covered in oil. It should be 100% reliable with no missed pulses.