Small DIY Hall Sensor

sportage4x4 · Post by **sportage4x4** » Mon Mar 06, 2006 6:57 pm

any leads on a relatively small hall sensor (to-92 package, or there about) that i can use to count ferrous gear teeth?

a 16 tooth wheel at 8k rpm is what its going to be reading. my math puts that at 128khz.

i've checked out the melexis US5881 but i cant find a max speed for it. digikey lists a hall sensor for a cam lobe from melexis as well, and it has a quoted bandwidth of only 15khz.[/url]

lapuwali · Post by **lapuwali** » Tue Mar 07, 2006 10:12 am

Your math is off fairly substantially.

8000rpm = 133 crank revs per second. x 16 teeth = 2133 tooth pulses per second, or 4266 transitions per second. If this is in a distributor, then it's half that. A 15kHz sensor should be plenty.

sportage4x4 · Post by **sportage4x4** » Tue Mar 07, 2006 4:34 pm

yeah, sorry about that, i dont know where i got 128khz from. i think i forgot to divide by seconds.

78Spit1500Fed · Post by **78Spit1500Fed** » Tue Mar 07, 2006 5:09 pm

If you're looking to read magnets, then you need a Hall sensor. If you're reading a steel wheel, you need a variable reluctance sensor. (If you're looking at VR sensors and see that they are "hall type" sensors, that means they do not output voltage, rather they switch a load.

-Brian

sportage4x4 · Post by **sportage4x4** » Tue Mar 07, 2006 5:20 pm

i need to read a steel gear, but i do not want VR and all its associated conditioning circuits. this is going into a noisy environment.

the MLX90217 from melexis is exactly what i need i think. its a hall sensor for counting gear teeth (and cam lobes...) and uses a bias magnet mounted behind the sensor.

GeorgeGt · Post by **GeorgeGt** » Tue Mar 07, 2006 9:42 pm

looks like it will do the job for u

also found this , but its probably too big for u http://www.elfa.se/pdf/73/734/07349038.pdf

sportage4x4 · Post by **sportage4x4** » Mon Mar 13, 2006 6:40 pm

update:

i've built a small hall sensor using the MLX90217. basically i just glued a small neodymium magnet to the back side of this IC, used a 2k2 resistor for a pull-up to 5v and it works flawlessly. i've tested Vdd anywhere from 5v right up to 24v and havent had any problems yet. with my 16 tooth wheel i cant find its top speed, i can only spin the wheel to 9500rpm. this will work fine for my application, as i will only see 8000rpm maximum.

newtyres1 · Post by **newtyres1** » Tue Mar 14, 2006 5:00 pm

Thanks for the update, I was looking for something similar some time ago but found nothing suitable, this device however looks like just the ticket. I now have new and much more desirable possibilities to explore. I assume this will be OK for an ignition set-up, i.e. no switching delays with increasing revs?

Ian.