Speed/hall sensor types

[THRobinson]

Hey guys, I know very little about electronics, just the bare basics with semi-decent soldering skills.

I am building a guitar pickup winder. To be cheap and easy I could buy this

5 digit display with sensor
https://www.ebay.com/itm/223331093919

It's battery powered for the display but works and reads 1200rpms. The motor I will be using is a 12v 1200rpm, and I need 5-digits because pickups are around 18000 windings.

I would however like a powered display
https://www.ebay.co.uk/itm/293493654999

Looks like rpms are fine, 5-digits, etc... Where I got lost was the sensor. NPN, PNP, closed, open, 2wire, 3wire....plus the digital display has no reset, which I assume is simply a momentary switch attached?

Hoping to get some advice... Again, no biggie to use the battery lcd, it's already done and ready to go, just rather the led display because easier to read. Looking to run off a 12v power supply... Has 2 motors, 1200rpm and 10rpm, both 12v. Will connect a motor controller to each for speed and reverse. Thanks.

[THRobinson]

Anyone?

[mikerj]

The input is active low, so you need a sensor that pulls it's output to ground when it detects whatever you wish it to detect.  For a hall effect or inductive proximity sensor you want a NPN output (it does say this on the last picture).  You may be able to use a simple reed switch, though 1200 RPM may be too fast for reliable operation so I wouldn't recommend this.  Likewise the reset input is active low, so a push button switch wired to 0v and the reset input should do the job, assuming the counter has it's own pull-up resistor on board.

Since the LED counter does not come with a sensor, so the final cost will be well above the LCD display counter that does come with it's own sensor.

[thatguy1988]

See the following page for information about Hall sensors including the difference between PNP and NPN type.


https://thesensorshack.com/sensors/hall-effect-proximity-sensor/

You will need to choose a high frequency Hall sensor. They sample at frequencies up to 30 kHz, which to be honest is not enough for very high frequency audible sounds, but I don't know what the highest frequency note on a guitar is. You could also consider an eddy current sensor which is like an inductive sensor but with an air core (instead of an iron one). It can sample at up to 100 kHz.

I just saw that the sensor you posted counts at 20 Hz, that is very slow! Actually it says that it is an inductive sensor, these work at lower frequencies than Hall sensors because they consists of a coil wound around an iron core, excited by An AC signal and the iron core has a sort of electrical inertia which limits sampling rate. As a said in the previous paragraph, an eddy current sensor has an air coil and therefore has a sampling rate faster than even Hall sensors.