I am looking to measure the speed of a roller and have played about with a hall effect sensor and a signal magnet per rotation.
What I am looking for is something that can have 60 pulses per revolution. I have been looking for a toothed wheel which is magnetic to use with a hall effect sensor but I am struggling to find something suitable as all the wheels I find are always 60-2 wheels as used in car engines.
Since I do not care about overall position I just want to measure speed I think having a 60-2 is just going to complicate the code and operation that the controller will perform.
I literally just want a high frequency of measurement by using 60 teeth rather than just 1.
Alternatively I could move away from hall effect and look into something else if anyone has a suggestion of a setup which will give me a high low digital output I can use interrupts to measure the time interval between.
I infer that 60-2 means there are 58 teeth. So why would you not just count 58 pulses per revolution? If having all 60 equally spaced is critical, just monitor millis() in your loop() to discover the timing gaps and fake those two that are missing.
I'm after measuring exact speed and then acceleration over known time. I am not worried about the exact position of the roller.
Another bit of looking around suggests perhaps a variable reluctance sensor maybe better. Then a plain metal wheel can be made without needing magnetic teeth?
Hi
Modern cars use hall sensor with a magnetic abs sensor e*bay search for - magnetic reluctor
VR sensors don't too work well at low rpm, when wheel speed < 5 mph.
cheers
peter
Thats why I am now thinking of the VR route, the original question was about hall effect which I think would be nicer, but having a suitable trigger made up is harder than one for a VR sensor.
I'm most familiar with farm machinery and often times inductive proximity sensors are used to read RPM. No magnets required, just a periodic piece of metal passing past the end of the sensor, often teeth from a sprocket. They typically run at between 12 and 24V, but you can read voltage across a resistor (divided) into the arduino. The sensor signals using current, so you have convert that to voltage by reading potential across a resistor, which you can choose such that it gives you a 5V signal. When no metal is near the sensor, you will read full voltage across the resistor, when metal is near, the voltage will drop to zero.
You can search this forum for inductive proximity sensor. Several folks, including me, have talked about how they interfaced these sensors with arduino.
You don't need the gear to be magnetized to use a hall effect sensor. Position a magnet and hall effect sensor so that the path of the magnetic field through the sensor is affected by the position of the teeth.
Maybe like this, or perhaps with the sensor near the teeth and the magnet next to it.
polymorph:
You don't need the gear to be magnetized to use a hall effect sensor. Position a magnet and hall effect sensor so that the path of the magnetic field through the sensor is affected by the position of the teeth.
That is SO good, Can the teeth could go between the magnet and the pickup, rather like an opto? .
You can probably place the magnet and hall effect sensor on either side of the gear teeth. The important thing is that the teeth going by distort the field to the sensor.
It will depend on the sensitivity of the sensor, strength of the magnet, and the relative sizes of the magnet and gear teeth.