Sensitivity of Hall sensor

[Andy in Finland]

Hi!

I've got my SpokePOV built & running , but I'm having problems trigger the Hall sensor with a magnet. I'm finding that the magnet needs to be within millimeters of the sensor, which isn't too practical. I've experimented with the orientation of the magnet, so the North-South'ness isn't an issue.

I've built the SpokePOV for red LEDS so it's using 2 cells. I checked the datasheet for the Hall sensor & notice that it's rated down to 4V. It's got me thinking that the sensor may be less sensitive at low voltage. Has anyone had similar experiences? Is the 3-cell configuration more sensitive?

I'm going to look for stronger magnets too!

-Andy

[adafruit]

it does need to be close. all hall effects tend to be like that. it is much more sensitive to S than N. You can stack a couple magnets

[sparr]

Are you sure that the magnet is in "front" of the sensor and not "above" the sensor? That is, if you did not bend the leads of the sensor, and you are looking at the bike from the side with the spokepov mounted on the wheel and pointing upwards, the magnet should be located in the up direction, not the towards-you direction. If you DID bend the leads of the sensor 90 degrees, then the magnet should be between you and the sensor, not upwards from the sensor.

[Andy in Finland]

Thanks for the replies.

I'd already bent the sensor so that the sensitive side is facing the magnet. Boy that was hard to explain without a diagram

I scouted around and found a more suitable magnet. The kids have a magnetic dart board & the darts work just fine to trigger the SpokePov. The magnets in the tip are surprisingly strong & the plastic shaft of the dart can be easily fixed to the front fork of the bike. There are similar darts at this page: http://www.fatbraintoys.com/toy_compani ... 3_pack.cfm

Now we need to wait for dry weather to try out the installation!

-Andy

[kayrock66]

You may be trying to use ordinary magnets, like from a kids toy. The one that Ladyada sells is particularly strong and this gives a better distance. I've gotten strong magnets out of old harddisk drives for the read head mechanism. It may seem like they're welded onto the drive chassis but its just the strength of the magnet.