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Topic: Hall effect sensor used as speedometer (Read 194 times) previous topic - next topic

faina

Hi everybody!
I have to realise a speedometer using an Hall effect sensor in order to measure the angular speed of a flywheel. I was thinking about drilling my flywheel and put a magnete in the pierce so that the magnete will rotate with the flyweel (I'll drill the flywheel two or four time to maintain the balancing).
As the magnete gets into line with the Hall effect sensor, the sensor will count 1 round. Otherwise it will count 0. In this way the Hall effect sensor will count "1"once per round.
That's how my speedometer will work.

I don't know which sensor I have to choose because I haven't got any knowledge about sensors.
My budget is max 15€ and my flywheel will rotate at max 3000 rpm.
Which sensor do you suggest me to buy?
I read that non latching sensor best fit in my case cause it's easier to write the code. If you could suggest me a model you think could be ok for me I will really appreciate that.

Thanks everybody!

mikb55

#1
Oct 13, 2018, 05:24 pm Last Edit: Oct 13, 2018, 05:45 pm by mikb55
Do you have access to the end of the shaft? If so, just glue a 10mm x 3mm bar magnet to the end so that it is symmetrical about the axis with the poles 90 degrees to the axis. If the shaft is steel then adding a 10mm non magnetic spacer between the shaft and the magnet will help project the magnetic field outwards making it easier for the sensor to detect it.
I've used the A3144 hall effect switch, but any cheap 'hall effect switch' will work. Taking the average of 50 readings will give you a resolution of about 0.1Hz.

wvmarle

There are more options.

If there are holes in the flywheel already, this can be used for optical (break beam) sensor.

A reflective (white) dot on the otherwise non-reflective axle (or the other way around) can be detected by other optical sensors.

A small magnet attached to the axle (or two for balance) can be read by either a hall effect sensor or reed switch.

For higher resolution attach an optical encoder to the axle. Those give you typically about 20 pulses per rotation.

All this can be done easily within your budget, no problem there.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

hammy

Drilling holes in flywheels is not a good idea as it may weaken it or create imbalance .

faina

@mikb55
Yes I have access to the end of the shaft. My flywheel is in aluminium!
I looked at the sensor you suggested and I think it's ok but could you tell me other sensors you think could be ok for my application?
I'd like to make comparisons between them and I'm interested in this stuff but I don't have any knowledge cause this is the first time I put my hands on Arduino and its sensors!
I'm interested in non latching sensors that can bear my angular speed! I really don't know how to choose them and when I read technical specifications of this sensors I don't understand anything!
If you could suggest me other sensors you will be very helpful (you already are)!
Thank u so much mikb55

@wvmarle

Yes I know that encoders or optical sensors are used for this application but I have to use Hall effect sensor because it was specifically requested from my professor.

Any advice about which model to choose?

@hammy

Yes I agree with you. That's not the best choice but it's compulsory for me to do that for my university project. Any advice?

Thanks everybody!

wvmarle

Yes I know that encoders or optical sensors are used for this application but I have to use Hall effect sensor because it was specifically requested from my professor.
Even professors can come up with an XY problem. Maybe that's all he knows, in which case it's your job to do the research and come up with better solutions for the problem at hand.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

mikb55

I really don't know how to choose them and when I read technical specifications of this sensors I don't understand anything!
Use a magnetic field calculator such as the one at https://www.kjmagnetics.com/fieldcalculator.asp to find the field strength 2 mm from the end of the magnet.
Look for a sensor that triggers below that value and has a frequency response in the KHz range.

cattledog

Quote
Any advice about which model to choose?
http://www.littelfuse.com/products/magnetic-sensors-and-reed-switches/hall-effect-sensors.aspx

I've used the 55140 three wire open collector sensors in several rpm measuring systems with small neodymium magnets epoxyed on the rotating wheel.

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