Pov not triggering every revolution?

[mchicago]

Ok, I'ld like to say firstly, I'm blind. I'm blind because I've been staring into the LED's on my spokepov for about an hour at near point blank range and having come up here to search the forums, have realised how blind I am. Great.

My actual problem is this - I have built the spokepov, and attached it to my bike wheels, and attached a magnet (using magical "sticky backed plastic" aka sellotape) so that its *nearly* touching the sensor. What I get when I spin it is just one led (on each side) on, then Occasionally, it jumps into life and produces the default bio-hazard output. When I say occasionally, I would say maybe every 40 or so revolutions of the wheel.

Having run out of magnets to try (I have tried different magnets) am I just using magnets which are too weak, or could this be a problem with my circuit?

Best regards,
Temporarily blinded in the Uk

[adafruit]

are you using the magnet sold at the adafruit.com shop or are you using some other kind?
"dark brown" magnets will not be good enough
you need a 'rare earth' (chromed) magnet
south side to the sensor

[mchicago]

I am not using the type sold at the adafruit shop for I had not really considered the magnet when I was buying (I was also trying to buy as little from adafruit because of nasty buggering import tax (damn them)).

I will go out tomorrow and see if I can find a rare earth one.

You interest me by saying the South Side - does the hall effect detector know the difference.

[mchicago]

Success! I have just got hold of some "Mega Magnets" from the local Maplins:

http://www.maplin.co.uk/Module.aspx?Mod ... &criteria=

These are triggering the sensor every time without fail, even over a distance of 2-3 cm. I'm not convinced its attached to my bike very securely, but this I can solve (I'm lucky in that I've attached it to a wheel with a disk brake, but the mounting support for "normal" breaks is still there, so I can build some kind of bracket which will fix it on permanently.)

Thanks so much for coming back on my query so fast, and as you say, I noticed it did matter which way round the magnet was attached. I am surprised that matters, but then I know very little about how hall effect sensors work.

Illuminated in the UK

[mikeyp]

hot glue is the best way to secure it imo

[cafe_latte]

old 3.5" hard drive magnets work great too.