Variables in Flowgraphs

This page describes the fundamentals of a flowgraph: how to make and edit variables, and data types. The flowgraph from the previous guide (Your First Flowgraph) will be used as a reference.

Variables
A GNURadio flowgraph is a .py Python file. Just as Python code can have variables so too can a GNURadio flowgraph by using the Variable block.

Every new flowgraph starts with the samp_rate variable:



GNURadio blocks are implemented as functions and can take parameters which modify their behavior. All of the blocks in the flowgraph above use samp_rate as a parameter. Create a new variable block by dragging and dropping it from the block library on the right:



Double-click the variable_0 block to view and modify it's parameters.



The Id field is the name of the variable. The variable is going to represent the frequency of the Signal Source block, so edit the name to frequency. Now edit the value to 4000.



Click OK to save.

Double-click the Signal Source block to :



You'll notice that samp_rate is the variable being used for the Sample Rate but Frequency is hard coded to 1000.

TODO: make/edit variables complex vs float (blue vs orange) compare the python .py code with the visual GRC flowgraph