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Author Topic: Help please :) LED controlled by wheel rotation  (Read 1322 times)
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Hi all...any electronics experts on here :p

I have built a small childs toy...it has 10 leds around the rim of the wheel (evenly spaced)

I want it so that when pushed along, only the 4/5 LEDs facing forward light up. I have a magnet that can be used as a rotation/speed sensor...but need this linked up to an arduino to control the illumination (unless you can think of a simpler method)

They can be lit up just after reaching the top of the rotation and swtiched off after 1/3 turn - the blur will make them appear to be on for a half turn. Should give a nice illumination arc at the front of the wheel

Thoughts?

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I don't think you connected the grounds, Dave.
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Could you do this with a slip-ring arrangement (made from a PCB), with breaks in the rings?
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That seems a bit complex

I saw this on ebay. This would be perfect

Just need it so that it is times correctly i.e. low RPM vs high RPM I want to ensure only the forward facing element lights up

http://www.ebay.co.uk/itm/130590643474?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_3804wt_1011

But with the example above, i'm pretty sure it activates when passing the sensor (magnet) with no consideration for RPM so the light on / light off point will not be constant on the wheel (talking with reference to the "hello" message)

Thoughts?
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How do you get power to the leds on the turning wheel rim? Battery inside the wheel?
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Yes can be any method. As it is just a childs toy, wheel balancing etc does not have a huge impact

So thinking I need a PIC with some timing logic based on the frequency of the sensor being activated (same way bicycle speedos work - magnet passing a reed switch i think)
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So you haven't built anything yet?

You could set the led leads so they can be contacted at two different radius on the inside surface of the wheel and then put brush contacts with battery and one resistor on the chassis to touch at those radius. You won't need an MCU. How wide your brushes are would determine how long the leds stay lit. Brush position would determine where they light. Sure, it's electro-mechanical but that's all you need!


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Quote
Sure, it's electro-mechanical but that's all you need!
I think that's what I already suggested.
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We are on the same page but Theta seems to be reading a different book.
Perhaps the PCB part seemed complicated? Or the words slip ring? Easier to use an MCU? I don't get it....
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Hmm...I see where you are coming from

But I do not like the electro mech approach.

I know that with the right arduino programming, it could calculate RPM and adjust the on/off position of the light and also the duration it needs to be on for

This will take advantage of visual stay effect
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Where I'd use longer contact surfaces.  smiley-cool

Oh well. If you put a magnet in the hub and a hall sensor on the chassis or vice versa then you have a good way to know orientation of the wheel. Or you can go with optical.

Still, how you get power to the leds from the controller(s)? Will you put batteries -in- the wheels? You see that you will need contacts if power and controller are in the chassis unless you do something really wild?

ps, maybe not so wild -- if the wheels have not leds but translucent plastic then it could be lit by light on the chassis. There are ways and then there are ways.

« Last Edit: October 25, 2011, 10:27:17 am by GoForSmoke » Logged

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With LEDs evenly spaced round the rim the electro-mechanical solution seems simpler and more robust to me.
The link that Theta provided http://www.ebay.co.uk/itm/130590643474?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_3804wt_1011 though was for a device with 14 LEDs in a radial line. It produces some 40 patterns which is quite clever, and a processor makes sense for that.

What is the diameter of this wheel?
What will be the range of rotational speeds?
Presumably it can be rotated back and forth?
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Well the E-M way as described will always light the leds contacted whether the toy moves or not and possibly that is not desired.

Something really cool would generate its own power when pushed, maybe use piezos or the old magnet and coils.

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Just FYI, there was a very successful kickstarter project this summer that accomplished exactly what you're trying to do for bikes.  Maybe you could look over their design to see if something similar might work on your smaller scale?

http://www.kickstarter.com/projects/revolights/revolights-join-the-revolution
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