I'm looking for a hall effect generator

Thanks for reading this post. Have you ever seen a bicycle generator? They are little flip down dynamos that spins as the bicycle wheel turns. Here's a link to a picture of one.

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I am wanting something similiar to that in size. But I am not looking to light a light bulb, I am trying to get the square wave the rotating magnets (in the dynamo) produce. I thought if I had a high speed DC motor, I could use it in the same fashion but have the benefit of roller bearings because of the high speed it will be moving. I am not trying to reinvent the wheel, just use something that is out there. But I am having a helluva time finding it. :)

I could email you a drawing of what I am looking for in hopes that what I am saying will make better sense. Thank you for taking to read this Todd

Reply to
atljetmech
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Get a steppiing motor, aka synchronous motor. They produce something closer to a sine wave than a square wave, but at least the leads to each coil are brought out independently.

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Bill Sloman, Nijmegen
Reply to
bill.sloman

A PM stepper motor, like a PM alternator, will produce a signal that is proportional to speed in amplitude as well as in frequency. Same deal with variable reluctance sensors. Maybe you want an "incremental optical encoder"-- some are made with bearings and are fully enclosed.

See, for example:

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Best regards, Spehro Pefhany

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"it\'s the network..."                          "The Journey is the reward"
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Reply to
Spehro Pefhany

Thank you very much. I think you are right ... the optical encoder is the way to go. But they look very expensive. All I'm trying to do is generate one pulse from one revolution.

It looks like the ones I've seen are an overkill for what I want and are way complex. I feel like I'll be buying a lexus just to drive down to the mailbox.

I do like the idea of an optical encoder. You have my eyes looking in the right direction but now I'm looking at a pile of ball bearings trying to decide on which one to choose from.

Please advise. :)

Reply to
atljetmech

If you really need only one pulse per revolution, why not use what they use for bike speedometers? A magnet on a spoke, and a reed switch that closes each time the magnet goes by. The whole speedometer kit is really cheap- maybe $10.

-- John

Reply to
John O'Flaherty

If you're really doing this on a bicycle, you can put a LED on one fork and a photodiode on the other fork, and count the number of times the tire valve goes by. It's wider than the spokes, so you can tell which is which by looking at the pulse width. A little metal tube painted black on the inside will get rid of the ambient light well enough that this should work OK, if you have a bright enough LED.

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

The alternative is a magentic chunk of neodynium iron or samarium cobalt on the wheel and a Hall effect sensor on the fork. If your wheel is truly flat and true, you can have the magnet get close enough to the sensor that a Hall effect switch would do -like an Allegro A3240UA.

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If the wheel wobbles a bit, you might need to go for a linear magnetic field sensor like the Allegro UGN3502U

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driving a more complicated circuit to detect when the magnet goes past.

The nice thing about magnetic field sensors is that they are less sensitive to dirt.

Farnell stock a range of NdFe button magnets, and K&J Magnetics Inc. have a bigger range that you can buy from their web-site.

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Bill Sloman, Nijmegen
Reply to
bill.sloman

I agree entirely. Bike wheels can flex significantly during hard pedalling and cornering, though, so I'd worry about losing a lot of pulses if the sensor were near the rim, which is one reason for trying the optical approach. The magnetic approach is more robust, though, as you say--maybe put the magnet on the hub instead.

Cheers,

Phil Hobbs

Reply to
Phil Hobbs

That's OK, I'm not very busy at the moment and it sounds like an interesting project.

I live in a renovated sewer pipe as well so I've got a front and back door but no rooms. Anyway, long story short, a hall effect generator sounds like a really cool idea that I could put behind my front door.

I might be able to adapt it for some different type rooms which would be good too.

Let me know how you get on and sorry about the others in the forum prattling on about bikes. Next thing you know they'll be talking about politics.

DNA

Reply to
Genome

Then all you need is a disc with a hole in it, an LED and a phototransistor.

Reply to
Homer J Simpson

While generator type solutions are velocity-sensitive, there IS a workaround; something called Wiegand wire. A properly treated magnetic material is used, and delivers clean pulses when the thing flips polarity. No moving parts, not confused by ambient light or dirt, it was an element in some auto distributor sensors.

Hall effect sensors weren't as rugged.

Reply to
whit3rd

an optical encoder (incremental type) can generate square wave pulses who ever, it requires you to power it it! the most basic ones require something like 10..24 Vdc..

-- other choice i guess if you want to go the root is using something like a stepping motor or an AC tach generator which will give you pulses proportion to your rotation. you will just need to pass the signal into a compression and shaping circuit to get your square wave your looking for.

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Reply to
Jamie

Dunno how you are for furntiure DNA, I got some spare stools if you want 'em.

They're a kind of bilirubin color.

Reply to
Borat

On Wed, 04 Oct 2006 13:11:53 -0400, Phil Hobbs wrote in Msg.

C'mon guys -- every damn bicycle "computer" on the planet, or at least every one I've had, works with a small permanent magnet mounted to a spoke and a reed contact on the fork. Tolerances are on the order of several mm. And properly tensioned wheels don't flex a lot less anyway, otherwise the brakes woule be rubbing all the time.

To the OP: Just get $10 bicycle computer and rip it apart to get an easily mountable magnet/reed set.

Why do something electronically when it has been done electromechanically millions of times?

robert

Reply to
Robert Latest

Erm i dont know if this is of any help, Ive just taken apart a very old hard disc drive to use the spindle motor to spin an experiment 10k-30k rpm its got 3 hall effect sensors in it, im sure you must know someone whos got a dead hard drive, it was quite easy to make a circuit to drive the motor from the hall sensor once i figured out the 12 leads, but you only need the hall sensors.

Colin =^.^=

Reply to
colin

Because reed relays are fragile and relatively bulky and they have a finite life - of the order of ten million operations.

For a regular bike that travels 2.2 metre per reed closure, this is

22,000 km or about 14 thousand miles. When I've used my bike to get to work, I've done about 10km per day - 20km is probably the top end of the normal range - which is roughly 2,500 km per year, which means that the relay is going to fail long before the bike does (I'm the third owner of my bike, and I bought it in 1979).

You can do ten times better with a mercury-wetted reed relay, if you can mount it vertically, but they are relatively expensive and not easy to get hold of.

Hall effect magnetic field sensors were something of a novelty when I first used one in the way, back in 1978, but if cheap bicycle computers still use reed relays it has everything to do with design inertia, and nothing to do with good design.

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Bill Sloman, Nijmegen
Reply to
bill.sloman

Why in the _world_ are you suggesting using a DC motor to drive a generator?

Just slap an inverter on the DC - or even an oscillator and amplifier.

Good Luck! Rich

Reply to
Rich Grise

the stepper fotor from the lead screw of a defective floppy drive will give you a signal something like that, (in a fraction of the size and easier to turn than the dynamo)

you'll need to feed it to a schmitt trigger to get a square wave from it though.

Bye. Jasen

Reply to
jasen

they were using them in PC mice until recently, if you have an old ball mouse lying around it'll have two in it.

make one. use a led and photo transistor and a disk with one hole in it.

you could modify the disk from an old mouse - (gum up half the slots with glue and paint it black, break the other half away)

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Bye.
   Jasen
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Reply to
jasen

stick it near the hub where that's less of an issue. some speedometers use reed switches instead.

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Bye.
   Jasen
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Reply to
jasen

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