Reading RPM from hard drive with hall effect

Hi everyone!

I’m trying to build the HDD POV Clock but I’m having problems reading the RPM (the label of the disks says 7200 rpm, it’s that too much?). I’ve started with a code and a circuit that now I know its not the correct way to do it. I was reading this article http://www.arduino.cc/playground/Main/ReadingRPM but I’m not sure how to connect the hall effect sensor. It’s just 2 pins of the sensor to Vcc and Gnd, and the signal pin conected to pin 0?

The LED and 10k resistor needed to be there for this to work.

Why is that? And how they are connected?

I’m using a “latching” Hall sensor, is that a problem??

In my original code I was trying to measure it with AnalogRead → when the magnet in the plate is right in front the sensor I get a certain value (183), so…

if(analogRead(A0)==183)
revolutions++;

That definitely not work :frowning:

Thanks in advance!

That definitely not work

Perhaps something like:

int val = analogRead(A0);
if(val >= 180 && val <= 187)
revolutions++;

7200 rpm is 120 revolutions per second.

That playground article definitely needs something better than a phone camera image. A schematic would be useful.

The person that posted that article appears to still be around. Perhaps a PM encouraging some improvements to the page is in order.

Thanks for the answer!

Yes, I’ve tried making a wide range with if(val >= 180 && val <= 187), but still not working properly. I’m going to try using attachInterrupt() but I have to sit a study a little bit before that :P. And also change the sensorI’m using, because its a latch type sensor and maybe an unipolar type will work better… I will come back later with more questions :grin:

Thanks!