1. Blackfin Volume Control
Aaron Greenwald
December 3, 2018

2. Outline
About
Goals of Project
Code Description
Conclusion

3. About
The device is being used as a volume control device that takes an input signal, changes the singal by through shifting and multiplication, and then is heard through the conputer’s speakers. When the button corresponding to specific volume levels lights a linked LED.

4. Goals
First and foremost I wanted the volume to change with the push of a button: done.
Secondly I wanted the LED’s to work properly. They needed to be independent of each other, light on the first press and turn off on the second press: done.
I’ll talk here…

5. Secondary Goals
Third is the button also needed to call the portion of the ISR that called my volume control section: done.
For improvements on the current project, I would apply a filter or some other method to avoid the high volume clipping. More improvements would include a timer to increase and decrease the volume over time or save the sound input to the memory and play at back at two different volumes.

6. Code Description
As with our previous labs, Initialization starts the different processes including the activation of the LED’s, button inputs, and audio input/output.
Talkthrough, the header file, initializes all the non-local variables.
Process Data is a small section that connects the speakers properly.
Main is similar to the header file with the declaration of variables, void routines, and our transmitter and receiver buffers.
Interrupt service routine is where the main portion of my code.

7. Code Continued
I first declared the LED’s and set their initial value 0.
The second portion activates the led’s, turns on the speaker inputs and outputs, and calls up the volume control routine below. The end of this section causes all the LED’s to work independently of one another.
The third section tells the program what to do on the second press of a button, to go back to its original position and initial values.
The fourth section changes the volume. This is where the code works properly.

8. Code continued
I first call up a temporary variable that I labeled as sound and set it to the left and right inputs shifted 8 times. This shifts the sound from a 24 bit to a more usable 32 bit input.
Then I create another temporary variable and set it to 35,000, a value that one of my class mates helped me arrive derived from the filter equations.
I then multiply these two values together to get the final value I need.
After this multiplication I can shift it any amount of units to either have no change (shift = 7), an increase (shift < 7), or a decrease (shift > 7).

9. Conclusion
The project worked as desired with the exception of some clipping of my signals at high volumes. It could have been more complex but I was expecting to work with Steven and Teresa on it and got a bit of a late start. I hope it is to your satisfaction.