need help with one of those magnetic flow sensors

[jag_e_fattig]

right now i'm in the process of building one of these. but i'm having some problems. I've hooked up some led's to the circuit to test it, but when i power it up both of the led's turn on. it doesn't matter how much i wave the magnet over the sensor, nothing happens. can anyone help?

[Dix Dogfight]

I took a peek at the link but couldn't find any schematic over the "flowsensor" (maybe I'm just blind) so if you could provide some info on how you have connected the stuff that would make it easier for us to locate any faults or errors.

/Dix

[BillA]

that is a "Hall Effect Sensor", not a magnetic flow sensor
you need very small discrete 'pulses' close to the pickup
I don't think waving a big magnet about will do the trick

[jag_e_fattig]

i did exactly what it said in the article. i even got some of those 1/8" rare earth magnets from radio shack . it's not like i'm waving a horse shoe magnet at it...

[Dix Dogfight]

Bry dig inte så mycket om herr U, han vet inte vad han snackar om. Jag har inte tid att svara just nu men du kommer att få ett utförligare svar imorgon.
Sov så gott.

/Dix

[bigben2k]

Did you run the test, as described?

(Qu'est-ce qu'il dit l'autre?)

[Dix Dogfight]

I'm gonna start off with a little theory and then decribe how real life Hall sensors work. I'm leaving most equations out for now because they are not needed to describe how a Hall sensor works and it will simplify things.

Assume we have a Current I_x from C to D in the X-axis in a bar shaped carrier (see figure).
If a magnetic field is applied perpendicular (along the z-axis) to the direction of the current there will be a force F in the y-axis.
This force will push the electrons from one side of the carrier to the other = there will be a larger concentration of electrons on the right side (B). Hence the (-) sign on this side. And off course there will be a equal amunt of electrons missing on the
other side (A).
The differences in electron concentration results in a electric field (E_y) across the carrier. The resulting voltage V_ab=E_y*W, the Hall voltage, is measurable and is used in the Hall effect sensors.

How does this help us in practice then:
There are different types of sensors that use the Hall effect.
First one is a type of switch that switches when the magnetic field changes polarity.
Second type switches when the magnetic field rises above a preset level.
A third kind deliveres a voltage that is proportionell to the magnetic field.

Depending on what kind of sensor you have you must alter the magnetic field close to the sensor accordingly.

Example: Lets say you have the first type and you are waveing a magnet close to it. The switch would not react because the field doesn't change it's polarity.
If you on the other hand rotate the magnet = change polarity between N and S then the switch will react.

Hope this will help you some in your quest for safer cooling

cheers

Edit: damn spelling errors are all over the place

[jag_e_fattig]

bigben:
i did exactly as the guide decribed so, yes..

dix:
tackar så mycket för hjälpen. mycket uppskattat. ska gå och testa nu