question for souround project with rotation sensor


i just make a quick posting and say hello, i must have done a first posting so i can post links .. i place my question in my next posting. c.


i have a question regarding an installation i am working on. i want to place 16 speakers arround a rotating plattform and control the rotation of the music with the rotation of the plattform. (i link a picture about the idea at the end of the post..)

i am wondering which sensor will be the best to measure not only the speed of the rotation, but also the acceleration and the breaking. i am thinking also about things like pitching a sample with the starting rotation of the carousel .... or scrub through it ..

will this work with the memsic sensor ??

or maybe something like this :,3305,33053,3305302&arid=8047 that would be a little expensive..

i also found this: maybe with more the one magnets ..

thanks for any advice, i am totally new to arduino. i also made a quick sketch about the idea, i hope its understandable.. heres the link:

all the best chris

Simple solution: the motor that rotates your platform will probably be geared down by at least 100:1. Assuming it's 100:1, if you count the revolutions of the motor, and you'll know where your platform is within 3.6 degrees. This can be done with a very cheap optical sensor, or a Hall Effect sensor with a magnet. Add a similar sensor to the platform to signal a "home" position, and you get an absolute position, plus the ability to compensate for errors in your ratio calculation, belt slipping, etc.


thanks for your reply. i think i should have mentioned that the plattform has no motor. its a plattform used on playgrounds, you sit on it and rotate it and they run for a while .. but anyway its not a big difference i guess. the thing is, if one turns the plattform and lays down on it with his head to one side. you think it is possible to have the sound follow his head ? can i do this with a magnetic sensor ? could you please post a link of the type of sensor you mean. greetings chris

its a plattform used on playgrounds

I assume you're not allowed to modify it.

If the outer edge is smooth, you could put a wheel like this on a base that holds it against the platform, and count its turns. Add a strip of tape to the platform for the "index" mark, and you can measure speed and position without any permanent change.

The magnetic sensor I was thinking of is one like this. They're often used for tachometers. Attach one or more magnets to the rotating part, and count the pulses to determine speed.

thanks, the idea with the wheel is great !
i wanna put such a thing on an exhibition, i will have to buy it,
so its no prob to modify it …
all the best !!

i will have to buy it, so its no prob to modify it ..

In that case, I would suggest mounting a pulley on the bottom of the platform. Or a gear, if you can find one surplus or salvaged (big gears are very expensive). The "wheel on the rim" is a compromise to avoid if you can: it's not visually appealing, not as precise as a gear or pulley drive, and vulnerable to getting damaged or tripping someone when people run around the platform to spin it.

Since people will often want to spin the platform slowly (music is usually more pleasant if you're not vomiting from dizziness ::)), so you want to get many pulses from each revolution to get an accurate reading of speed and position. You will probably want to use the gear/pulley to make your encoder spin much faster than the platform.


ok, thanks ran. i will order the wheel sensor and try it out. all the best chris

How about putting the encoder-wheel on the inside of the turntable? Something like this?

yeah, thats great. i am not sure how exatly the wheel will look like, i am still searching for an affordable one... maybe i will it just make it on my own. the next days i will get my arduino board and will start playing arround. thank you all, it was great help ! greetings chris

How about putting the encoder-wheel on the inside of the turntable?

It's a good approach, in theory, and would be fine for many uses. I think there's a high risk of it running into problems in this particular application, because those platforms aren't very precisely manufactured. Rough surfaces, or even a slight deviation from perfect roundness, could make the coupling between the wheel and the platform unreliable, and screw up the accuracy of the readings.

If you use a real rubber/air-wheel, and spring-load the encoder-setup, I don't think there will be any problems.

i ll try it all out, it wont be too bad if its not 100% exact i guess .. greetings...cris