# Frequency controlled motor speed

I would like to control a 12v motor by frequency of pulses at 5v and a variable frequency from 4.44hz up to 800hz

Any ideas how I could do this ?

steve430:
I would like to control a 12v motor by frequency of pulses at 5v and a variable frequency from 4.44hz up to 800hz

Any ideas how I could do this ?

If this is all you want to do, there is certainly no need for an Arduino. A NE555 and a driver transistor will do it.

Paul

You really sound like you know what your doing, that’s a brilliant bit of advice I just don’t really know what to do next or how to apply this

If I tell you the application maybe it will shed some light on what I’m trying to do..

I have a classic car that we put a newer engine into and I’m trying to get the speedometer to read,
The original is a mechanical wire that gets turned by the gearbox and goes straight into the speedometer that uses magnets to convert the rotation into a speed count (1000 rotations per mile)

The new gearbox is an electrical pulse signal at 4.44hz at 1mph and goes up to 888.89hz for 200mph for example

From what I can tell the ne555 creates the pulse but I already have the pulse coming from the gearbox, sorry I should have added the Application to my original post

steve430:
I would like to control a 12v motor by frequency of pulses at 5v and a variable frequency from 4.44hz up to 800hz

You can't do that directly. The motor would spin at the same speed regardless of the frequency, if the duty cycle is fixed. Chances are the length of the pulses from the gearbox will get shorter as the frequency gets higher, because the pulses are coming from a mechanical/magnetic/optical sensor of some kind. So the duty cycle will be roughly the same at all frequencies.

You need to measure either the frequency or the pulse length (no point measuring both) and turn that into a fixed frequency signal with a variable duty cycle. Arduino can do this. Even a tiny45 chip (which you can program just like an Arduino) can do this.

So 1000 revolutions per mile = 16.666 RPM per MPH, 200 MPH = 3333.2 RPM. You want to drive the mechanical speedo with a motor that runs at 16.666 RPM with an input of 4.44 pulses per second and 3333.2 RPM at 888.9 PPS, or motor RPM = PPS * 3.75 (approximately) .
Is that correct?
BTW, how did you arrive at 888.89 PPS = 200 MPH?