Speed signal/one phase signal?

Hi. I purchased a new 2000w BLDC 72v controller for my fat scooter and i'm hooking it up and all seems to work fine.
I have no real Speedometer on it, only a simple voltage display.
I was thinking to develop something using arduino but I don't really know what the single cable Speed signal works.
it looks to be directly soldered to one of the 3 phases.(or possibly one of the hall sensors)

So I'm guessing the Chinese dashboards does something like this: counts the time between 2 pulses (=one rotation of the wheel, since it is only monitoring one phase) then calculating the speed using time taken for one rotation, and the circumference of the Tire? getting something like xxxcm in 250ms (then converting that to km/h)
or am I way off?

Yes, that is right you can get the signals from the motor phases or the hall sensors as its cadence is proportional to the motor rpms (Speed)

molokai said:

I was thinking to develop something using arduino but I don't really know what the single cable Speed signal works.

Click to expand...

There's quite a lot of arduino speedometer projects out there, if it helps:
https://www.google.com/search?q=arduino+speedometer
The main thing you'd need to do differently than most of them is add a voltage buffer for the variable but potentially very high voltage from the phase wire, and also filter out the PWM from the controller, which will typically be at several kHz.

It's much simpler to take one of the hall signals from the motor, or use a separate speedometer sensor.


Alternately, you can use a cheap bicycle speedometer, if the circumference of your tire is within the range it's settable to, and it is not just preset tire sizes (lets you set the circumference in mm's, etc).

If you want more functions, there are also "dashboards" available (one of them documented here by MJSFoto1956) that directly use that speedo wire from the phase of the motor you have.