How do I vary the sample rate of a block while the simulation is running?

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I'm trying to vary the simulation rate of a Limited Counter in order to make it count faster or slower in real time. (I'm trying to create a plant model of a crank wheel, where the rate of count of crank teeth will be a function of RPM.) I've created a variable in the MATLAB workspace and used it in an expression for the sample time in the counter. However, changes to this variable in the workspace only take effect when I restart the model, they are not read during the simulation. Also, I need to be able to increase and decrease the rate that the counter runs--i.e., accelerate and decelerate the speed the crank teeth go by--during the simulation, to check my model under development.
Is there anyway to write values to a variable used in the sample time setting of a block directly in Simulink while the simulation is running? e.g., use a slider gain and have the gain feed into the variable in the expression used to set the sample rate of the Limited Counter block? Or some other way to vary the sample rate during the simulation?
Thanks for any ideas anyone may have.

Accepted Answer

A Jenkins
A Jenkins on 28 Aug 2014
Edited: A Jenkins on 28 Aug 2014
I would start with a Programmable Pulse Generator from the File Exchange.
This will give you a programmable input for the frequency, which you can adjust with either a slider or with the set_param() command.
Then, if you need a counter instead of tooth-pulses, you can integrate the output of the Pulse Generator, perhaps with a detect-change block if you just want the edges.

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