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Mark Lanctot
2006-03-17, 18:17
<And now for something completely different!>

I got an exercise bike today. It's described as a "magnetic" exercise bike. I suppose this means the resistance is provided by a magnet acting on a ferrous disc attached to the pedals but I couldn't locate any technical details.

What to do while exercising - why, listen to the Squeezebox, of course! :-)

Except I couldn't. The SB kept freezing, stalling, dropping out. In short it performed the worst it ever had in the 10 minutes I was using this bike.

When I stopped, everything went back to normal.

So I guess my question is - would there be any way using this bike would cause EMI? By Faraday's Law, current would be induced in the disc - it would have to be. Would it then emit EMI?

It's a very cheap bike, so if the more expensive ones have any sort of shielding this one does not have it...

Hopefully no one thinks I'm a quack for asking, but the effect is dramatic and repeatable.

notanatheist
2006-03-17, 21:21
was the bike on the same circuit as the squeezebox? That has to be one bad piece of exercise equipment if it puts out that much interference. Are you using a wireless connection with the SB?

Mark Lanctot
2006-03-17, 21:29
No, the bike has no electrical connection. The small computer runs on two AA batteries.

It is a wireless Squeezebox3.

ceejay
2006-03-18, 02:54
Try some different wireless channels?

Ceejay

radish
2006-03-18, 09:46
The bike is likely built as a generator, with a variable (electrical) resistance to provide physical resistance. Assuming they just threw a bunch of magnets and coils together without much shielding it'll be throwing out EMI all over the spectrum.

Mark Lanctot
2006-03-18, 12:01
The bike is likely built as a generator, with a variable (electrical) resistance to provide physical resistance. Assuming they just threw a bunch of magnets and coils together without much shielding it'll be throwing out EMI all over the spectrum.

Aha - so I'm not crazy. :-)

ceejay: I'm a little bit hesitant to change wireless channels. I did a lot of NetStumbler sleuthing to find the right channel - I'm in a very radio-congested area. Also if the EMI is over a wide band it may not make much difference. However what I'll do in NetStumbler is graph my wireless connection's signal strength and start up the bike to see the impact.

notanatheist
2006-03-18, 13:27
I got it! Wrap the bike in aluminum foil! Actually, that may not be a bad idea, if you can isolate the unit spewing EMI try to cover it with a box lined with aluminum foil. It wouldn't cost you more than $2 to try and I'd love to hear the result.

CardinalFang
2006-03-18, 13:35
The bike is likely built as a generator, with a variable (electrical) resistance to provide physical resistance. Assuming they just threw a bunch of magnets and coils together without much shielding it'll be throwing out EMI all over the spectrum.

Are you sure that it'd reach the gigahertz spectrum though? I can see it getting into a few tens of hertz with the eddy currents in the disk and the speed of rotation, but not high enough frequency to upset a wireless signal.

The best way to check is to go wired if you have a long enough cable.

pfarrell
2006-03-18, 13:37
notanatheist wrote:
> I got it! Wrap the bike in aluminum foil! Actually, that may not be a
> bad idea, if you can isolate the unit spewing EMI try to cover it with
> a box lined with aluminum foil. It wouldn't cost you more than $2 to
> try and I'd love to hear the result.

Would work better if you can ground the aluminim foil to a well
connected earth ground. It might work to just ground the chassis of
the whole machine.

--
Pat Farrell pfarrell (AT) aframedigital (DOT) com
www.aframedigital.com

Mark Lanctot
2006-03-18, 14:02
Strangely I just did ~12 minutes on the bike and the Squeezebox worked flawlessly...

It was certainly reproducible yesterday.

Oh well, at least I got everyone's brain cells working. :-)

Wirrunna
2006-03-18, 14:49
Was the SB in the same physical location relative to the bike ? The rf from the bike may be quite directional.

Michaelwagner
2006-03-18, 17:31
Are you sure that it'd reach the gigahertz spectrum though? I can see it getting into a few tens of hertz with the eddy currents in the disk and the speed of rotation, but not high enough frequency to upset a wireless signal

He's a Canadian. No telling how fast he peddles :-)

Mark Lanctot
2006-03-18, 17:54
Was the SB in the same physical location relative to the bike ? The rf from the bike may be quite directional.

You may be on to something. The Squeezebox is directly in front of it, about 7-8 feet away.

Mark Lanctot
2006-03-18, 17:58
He's a Canadian. No telling how fast he peddles :-)

LOL!

Just to see how high I could get it to go, I reved it up to 45 km/h yesterday. But at that speed my legs are pumping up and down so fast I thought it was going to tip over. :-)

Most of my session yesterday was at 25 km/h. Today it was after I had to take a drive across town, which had me so frustrated I kept it at 30-35 km/h for 15 minutes.

In addition to being good for my health, it affords me some quality time with the Squeezebox. And it's nearly silent, so nothing to interrupt the sound...except for EMI.

Khuli
2006-03-20, 02:28
... so nothing to interrupt the sound...except for EMI.

Yes, I have some dodgy recordings by EMI too....

Mark Lanctot
2006-03-20, 06:30
Yes, I have some dodgy recordings by EMI too....

Better than Sony though. (http://forums.slimdevices.com/showthread.php?t=22115)

mattybain
2006-03-20, 08:46
<And now for something completely different!>

I got an exercise bike today. It's described as a "magnetic" exercise bike. I suppose this means the resistance is provided by a magnet acting on a ferrous disc attached to the pedals but I couldn't locate any technical details.

What to do while exercising - why, listen to the Squeezebox, of course! :-)

Except I couldn't. The SB kept freezing, stalling, dropping out. In short it performed the worst it ever had in the 10 minutes I was using this bike.

When I stopped, everything went back to normal.

So I guess my question is - would there be any way using this bike would cause EMI? By Faraday's Law, current would be induced in the disc - it would have to be. Would it then emit EMI?

It's a very cheap bike, so if the more expensive ones have any sort of shielding this one does not have it...

Hopefully no one thinks I'm a quack for asking, but the effect is dramatic and repeatable.

This is so spooky, I had the same problem yesterday when I tried to watch a movie on my wireless laptop the same time I used my electromag wind trainer (exercise bike). Thought I was going loopy as normally the laptop is fine for streaming video.

I did change the channel and it got a lot better, I just couldn't work out why it would happen.

Fifer
2006-03-20, 09:05
Do either of the bikes in question have electronic speed displays? If so, has anyone tried removing the battery?

Mark Lanctot
2006-03-20, 09:29
Do either of the bikes in question have electronic speed displays? If so, has anyone tried removing the battery?

Good idea, mine has a simple one - but I believe all the displays do is count the pulses generated by (I would imagine) a Hall Effect sensor as the wheel spins and use the pulses to calculate speed and distance.