Where To Find Hall Effect Sensor in old Electronics?

Go To Last Post
29 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi
I'm Unable to find any kind of Hall Effect Sensor in my region,
All what i can find are those expensive arduino shield which i don't like to work with (very big sized),
I used to find a hall effect sensor in some old pc fans but i don't have any fans left, So Geeks...

Where do you think i can find a Hall effect sensor in old Electronics?

Thanks

A Beam of Light out of the War

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

old floppy drives normally have one.(To measure rotation speed)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thanks for replying, Unfortunately I don't have any .
Any other?

A Beam of Light out of the War

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

What do you need it for ?

 

Perhaps a small coil with soft metal center that give a pulse every time a magnet passes can be used.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

in computer fans or old door/window security system

Last Edited: Thu. Apr 30, 2020 - 10:15 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

sparrow2 wrote:
What do you need it for ?

I'm trying to measure the rotation speed of a motor by gluing a magnet on it and using a hall effect and a microcontroller on the other side.

sparrow2 wrote:
Perhaps a small coil with soft metal center that give a pulse every time a magnet passes can be used.

I will consider trying that as a last try if i didn't find any hall effect sensor, Thanks

A Beam of Light out of the War

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

In VCRs

DVD and CD drives

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

dan1el wrote:
old (sic) door/window security system

old ones would use reed switches.

 

I wouldn't be surprised if new ones still do ...

 

@ AbDoO_   could a reed switch work for you?  How fast do you need to go?

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

awneil wrote:
reed switches.

Yep i already Tried Reed switches, unfortunately not fast enough.

A Beam of Light out of the War

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

So, again,  How fast do you need to go?

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

A pickup (as I mentioned in #4) can easy be made from the coil of a small relay. 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Try using a light-sensitive diode or light-sensitive resistor with an LED.   Paint a small cylinder section of the motor shaft black, then glue a small piece of aluminum foil at one spot on this black section of the shaft. Focus the LED onto the black shaft.  Position the light-sensitive diode directly in the path of the reflection of the light that bounces off the piece of aluminum foil.   Every revolution of the shaft will position the piece of foil for enough time to cause a voltage change on the sensor.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Car engines, used to detect engine RPM.

 

[EDIT]

Water flow meters

Coffee machines

Central heating boilers

 

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

Last Edited: Thu. Apr 30, 2020 - 11:26 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0


#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

If this works (many places it's to dirty), the old computer mice worked that way. (those that have encoder wheels)

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Which kind of motor ?

 

If it's a DC motor, you can "see" the speed as pulses in the current (there will then be a constant factor for poles and gear ).

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Simonetta wrote:
light-sensitive resistor 

I think they tend to be rather slow ?

 

Still we await a specification from the OP for what speed is required ...

 

frown

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Thank you everyone for replying,
I think i need a high speed sensor,
I'm trying the coil now... as well as searching in the electronics you mentioned
Thanks

A Beam of Light out of the War

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 1

I'm trying to measure the rotation speed of a motor by gluing a magnet on it and using a hall effect and a microcontroller on the other side.

 

You can use the ADC to measure the back-emf of the DC motor, works pretty good, after calibration.   When the PWM is in the off state, the motor acts like a generator, voltage highly proportional to speed. So take a voltage reading in the middle of the off time & you get a number proportional to speed.  Adjust the pwm duty up/down to get the speed you want.

This can also be better than hall effect, since by measuring the voltage, you instantly know the speed.  With the hall effect you prob need to take several samples (several rotations) before you know the speed.

 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Fri. May 1, 2020 - 07:24 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I used a method similar to AVRCandies' to get motor speed; counting pulses works but is tricky... there's a basic sinusoidal current signal with amplitude proportional to torque and frequency proportional to rpm, and commutator switching noise, very definitely not consistent between different motors from the same maker, or even motor direction.

 

Instead, PWM a speed at high frequency, and let the motor coast ten or twenty times a second, just for a millisecond. Measure the EMF generated during the coasting phase and adjust the PWM to suit. I have only a couple of hundred revs from motor start to motor stop and need to detect stall in that time, too...

 

Interestingly, with small motors I found (before settling on this method) that low speed PWM (200Hz or so) gave much better torque than 20kHz... I speculate the impedance of the rotor coils is turning the energy into heat instead of torque.

 

Neil

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Measure the EMF generated during the coasting phase and adjust the PWM to suit. 

 If you are running the motor to 100% duty, you have no choice--you must coast to measure. In some setups the motor may only run to, say, 75% max.  If the shortest off time allows, you may measure during that time & not need to switch modes (coast vs non-coast).

If you also measure motor current during the PWM on time, you can also have a torque limit.  You can use an RC filter and measure the current over several cycles & take into account the duty cycle. 

 

Measuring the current allows you to calculate the speed "droop" (due to winding resistance), which is another way of inferring the motor speed (knowing the applied voltage and duty cycle) & applying a correction.  Interestingly, if slightly too much compensation is applied, the motor will speed up with an increasing load and slow down when the load is removed (which seems rather strange when you physically try it).  You might expect this to result in a runaway situation, but due to nonlinearities it reaches a stable faster speed. 

 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Yes; that's why I was experimenting with lower pwm frequencies - I could measure the coast in the off time. But it takes a couple of milliseconds for the coast speed to stabilise through the rest of the circuitry before you can take a valid measurement. You don't have that time at 20kHz PWM.

 

Neil

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

But it takes a couple of milliseconds for the coast speed to stabilise through the rest of the circuitry

I just have a resistor divider and a very small cap at the adc, so the back emf is available "immediately" for ADC measurement.  The motor speed itself is "stable enough" during a single PWM off time (or else the PWM freq is pretty low).   However, if the PWM off time is very small (such as when you get near 100% PWM), you do indeed get pinched off.  So coasting & measure is inherently a more useful technique.  The other way is useful when the PWM duty is limited.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

barnacle wrote:
But it takes a couple of milliseconds for the coast speed to stabilise

avrcandies wrote:
The motor speed itself is "stable enough" during a single PWM off time (or else the PWM freq is pretty low).

Don't you need to at least wait for the decay of the transient due to the armature inductance?  A couple of milliseconds sounds about right for this (unless the motor is really small).

Letting the smoke out since 1978

 

 

 

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Most brushless fans will have a hall-effect sensor.  Spindle motors for CDs, floppies, etc are likely to have three.

 

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

 

Don't you need to at least wait for the decay of the transient due to the armature inductance?  A couple of milliseconds sounds about right for this (unless the motor is really small).

I'm thinking of maybe a 12V motor at 1-2 amps.   Here is an example where a motor (I don't know what this motor specifics are) is driven at 12.5%, the spike is pretty quick (1ms/div).

In this case the PWM freq is a low freq drive.

This drive has a simple parallel diode to clamp the motor winding, however this gives the slowest decay (0.7V clamp).  In many cases, no diode is needed & the motor clamps at the FET breakdown voltage (say a 60V or 100V fet).

 

since di/dt =transient recovery rate =Vinductor/L, the much higher voltage (100V vs 0.7V) results in an even faster transient dwindle.  

 

      

You definitely don't want to take your reading during the transient, so some delay factor is needed. If you get pinched off for sample time, then you need to revert to some sort of coast & measure (and coast as little as possible), or perhaps change to a slower PWM freq.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Sun. May 3, 2020 - 02:02 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Of course, nowhere has the OP said they are controlling a motor, only that they want to measure the speed of one.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Of course, nowhere has the OP said they are controlling a motor, only that they want to measure the speed of one.

That's a good point, the OP left that sort of open-ended; maybe he is building only a speed sensor/detector setup.  However, if he is controlling with PWM, as is often the case, it is pretty easy to measure the speed without any sensor (after some calibration).   In many cases no cal is needed, there is just some knob to adjust from "slow" to "fast", so you don't have any clue about the RPM anyhow.   I was surprised that a lot of people at various companies never heard of doing this.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Sun. May 3, 2020 - 05:27 AM
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

@avrcandies - I need to measure speed in both directions, so there's some minor complexity around the implementation of the full-bridge. I shall have to stop here; it's starting to get into our commercial IP.

 

Neil