Using BasicX Block Data Objects with PlaySound

Transcription

1 Basic Express Application Note Using BasicX Block Data Objects with PlaySound Introduction The BasicX system library includes a procedure called PlaySound, which can be used to generate audio signals from data stored in EEPROM memory. Block data classes are a convenient way to store mass amounts of data in EEPROM memory. Combining PlaySound with block data classes is an easy way to generate audio signals from sampled data. Hardware interface PlaySound utilizes a software DAC (Digital to Analog Converter) that generates sequences of fast digital pulses, which after filtering produces an analog voltage in range 0.0 V to 4.3 V. The circuit shown in figure 1 (below) can be connected directly to a speaker: Figure 1 Driving Speaker Alternatively, figure 2 shows a circuit that can be connected to standard amplified computer speakers:

2 Figure 2 Driving Audio Amplifier Software interface The syntax for calling PlaySound is as follows: Call PlaySound(Pin, StartAddress, Length, SampleRate, RepeatCount) Item Type Direction Description Pin Byte Input Output pin number. StartAddress UnsignedInteger Input Starting address of data in EEPROM. Length UnsignedInteger Input Length of data. Units are in bytes. SampleRate UnsignedInteger Input Sample rate. Units are Hz. RepeatCount UnsignedInteger Input Number of times to repeat the sound. 2

3 The StartAddress parameter can be obtained from the DataAddress property of a block data object. Here s an example program that shows how it works: Private SoundStep As New ByteVectorData ' 1 Sub Main() ' 2 Dim Address As New UnsignedInteger ' 3 Call SoundStep.Source("SoundStep.txt") ' 4 Address = CuInt(SoundStep.DataAddress) ' 5 Call PlaySound(17, Address, 1000, 1000, 1) ' 6 End Sub ' 7 SoundStep (line 1) declares a block data object that is similar to a 1D byte array. The SoundStep.Source method (line 4) tells the compiler where to find data to load into the object. The data is located in file SoundStep.txt on the PC host computer. The SoundStep.DataAddress property (line 5) tells us where the data is located in EEPROM. That address is used as a parameter to PlaySound (line 6). PlaySound reads 1000 samples at a sample rate of 1000 Hz, and plays the sound through I/O pin 17. Creating block data text files Block data files are regular ASCII text files that the compiler converts to binary form before loading into the BasicX system. In the attached demonstration program, we ll use 3 data files to generate data that are conceptually similar to the following waveforms: Figure 3 Step Waveform Figure 4 Triangle Waveform 3

4 Figure 5 Tremolo Waveform The 3 filenames are SoundStep.txt, SoundTriangle.txt and SoundTremolo.txt. A Visual Basic program was used to create the 3 files. Source code is included in a VB form file called frmmain.frm. All together now Program SoundFile puts everyting together and generates audio signals from the 3 data files listed above. Souce code is attached in file SoundFile.bas, and is listed below: Option Explicit ' This program demonstrates the PlaySound procedure. PlaySound generates ' sound from sampled data stored in EEPROM. ' ' A convenient way of storing data in EEPROM is through the use of block ' data objects, which read files from the PC host computer and downloads ' the data to EEPROM. ' These are read-only block data objects. Private SoundStep As New ByteVectorData Private SoundTriangle As New ByteVectorData Private SoundTremolo As New ByteVectorData Public Sub Main() Const OutputPin As Byte = 17 Dim Note As Integer Dim Length As New UnsignedInteger Dim SampleRate As New UnsignedInteger Dim RepeatCount As New UnsignedInteger Dim File As Integer Dim Address As New UnsignedInteger "Demonstration of PlaySound" "with block data objects" Call Delay(0.5) Call SoundStep.Source("SoundStep.txt") Call SoundTriangle.Source("SoundTriangle.txt") Call SoundTremolo.Source("SoundTremolo.txt") Length = 1000 RepeatCount = 4 ' Bytes 4

5 For File = 1 To 3 SampleRate = 1000 ' Hz Select Case File Case 1 Address = CuInt(SoundStep.DataAddress) " File SoundStep.txt:" Case 2 Address = CuInt(SoundTriangle.DataAddress) " File SoundTriangle.txt:" Case 3 Address = CuInt(SoundTremolo.DataAddress) " File SoundTremolo.txt:" End Select For Note = 1 To 3 " Sample rate = "; CStr(SampleRate); " Hz" Call Delay(0.2) Call PlaySound(OutputPin, Address, Length, SampleRate, RepeatCount) SampleRate = SampleRate * 2 ' Increase by octave. Call Delay(0.5) Next Next End Sub 2002 by NetMedia, Inc. All rights reserved. Basic Express, BasicX, BX-01, BX-24 and BX-35 are trademarks of NetMedia, Inc. All other trademarks are the property of their respective owners A 5