Demand Peripherals     Robotics and Automation Made Easy

TONEGEN: Audio Square Wave Generator

The tonegen peripheral generates audio frequency square waves with an adjustable volume. You can specify the frequency as a floating point number or as a music note. Volume is in the range of 0 to 100 and follows an audio taper. Note duration is specified in milliseconds.

 

Hardware:

The tonegen peripheral assumes that the four FPGA pins are tied to a 2R-R resistor network. Note this is _NOT_ an R-2R network. An R-2R network is linear while a 2R-R network is very non-linear. The non-linear nature of the 2R-R network gives a non-linear audio taper to the volume. The 2R-R network should be followed by a low pass filter with a cutoff around 20KHz. The cutoff frequency of the low pass filter is not critical.

 

Resources:

You can specify the frequency and amplitude of single note to play or you can specify a melody file of notes to be played.

note : note to play
The write-only note resource specifies the note frequency, volume, and duration. Frequency can be given as a floating point value in the range of 10 to 10000 Hertz. Frequency can also be specified at one of Ax, A#x, Bx, Cx, C#x, Dx, D#x, Ex, Fx, F#x, Gx, or G#x, where 'x' specifies the octave in the range of 0 to 8.

Volume is specified as a relative value in the range of 0 to 100. A value of zero turns off all audio output. Volume follows a logarithmic curve to match the audio taper of a typical sound system if a 2R-R resistor network is attached to the four FPGA pins

Duration is specified in milliseconds in the range of 1 to 4095.

melody : play a file of notes
The melody resource lets you play a file of notes. Each line has a frequency, volume, and duration. Lines which do not parse as notes are treated as comments and are quietly ignored. Use a volume of zero to add a quiet pause between notes.

The daemon changes it working directory to / when it starts. For this reason all melody file names must be fully qualified.

A typical file might appear as:

# Melody file with freq, vol, duration
g3 68 172
c4 73 172
e4 84 162
g4 83 384
e4 74 128
g4 86 1000

 

Examples:

    # 1000 Hz at half volume for 4000 milliseconds
    pcset tonegen note 1000 50 4000
    pcset tonegen note A4 100 100
    pcset tonegen melody /usr/local/lib/my_melody.txt