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RogueGeek

Launchpad Timer Reference Oscillator

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I'm working on building a speed controller for a belt grinder and I'm using a G2553 for the controller.  Since the speed of the motor will need to vary between 1000-8000 RPM, the 32.768Khz clock was too slow and the DCO was drifting too much and causing the RPM to vary by several hundred counts even when the motor was running at a constant stable speed. This in turn caused the PID loop to act really weird and I could not hold a stable speed.  What I needed was a stable reference oscillator to use for sensing the RPM of the drive motor. 

 

Being stubborn, I wanted to do this with only a single G2553 cpu and since the 2553 isn't spec'd to use a high freq crystal I went looking for an alternate way to provide a reference for the timers.  I was quite happy to discover that P1.0 can be configured as an input for an external timer reference. Thus the "Launchpad Timer Reference Oscillator" was born. 

 

In my application I'm using a 16MHz oscillator, but any speed could be used to fit the given application.

 

 

post-30416-0-41298100-1455408538_thumb.jpg

It is a small 0.3" x 1" pcb with an Abracon oscillator, a 0.1uF cap., and connectors.

 

It only took a minor code change to have the Timer use the external reference and so far it seems to have resolved my timing issues.

 

While this is without a doubt the most simple PCB I think I have ever designed, it just may turn out to be one of the most useful.

I will definitely be including an external reference oscillator in any of my future projects that need very accurate time references.

 

Here it is in action.

post-30416-0-35428200-1455408539_thumb.jpg

 

 

thanks for looking

 

Brian

 

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