How to play a DTMF tone

To play a Dual-Tone Multi-Frequency (DTMF) tone do the following:

• Constructing and initializing

• Configuring

• Playing

Use the CMMFDevSound::NewL() method to construct a new instance of DevSound.

After construction, use an CMMFDevSound::InitializeL() method to initialize DevSound to play tones. This method requires that you specify the DevSound observer class to handle callbacks.

Once initialization has completed, successfully or otherwise, DevSound calls the MDevSoundObserver::InitializeComplete() function.

The following settings can be configured before or during DTMF tone play:

• To set the duration of tone on, tone off and tone pause to be used during the DTMF tone playback, use the CMMFDevSound::SetDTMFLengths() method.

  IMPORT_C void SetDTMFLengths(TTimeIntervalMicroSeconds32 &aToneOnLength,
TTimeIntervalMicroSeconds32 &aToneOffLength, TTimeIntervalMicroSeconds32
&aPauseLength);

  This method has three parameters:

  • &aToneOnLength - the period over which the tone is to be played.

  • &aToneOffLength - the period over which no tone is to be played.

  • &aPauseLength - the period over which tone playing is to be paused.

  The internal configuration set by CMMFDevSound::SetDTMFLengths() lasts until it is recalled or for the lifetime of the current DevSound.

  Note: The CMMFDevSound::SetDTMFLengths() function is only available during tone play.

• To change the volume of the audio device to a specific value, use the CMMFDevSound::SetVolume() function. The volume can be set to any value from 0 to CMMFDevSound::MaxVolume().

  To define a period over which the volume rises from 0 to the normal volume level, use the CMMFDevSound::SetVolumeRamp() function.

  Note: The CMMFDevSound::SetVolumeRamp() function is only available during tone play.

• To set the speaker balance, use the CMMFDevSound::SetPlayBalanceL() function. This function has two parameters:

  • aLeftPercentage - the left speaker volume percentage.

  • aRightPercentage - the right speaker volume percentage.

• To set the priority setting for this instance of DevSound to access the audio device, use the CMMFDevSound::SetPrioritySettings() method. Priority settings are used by the Audio Policy component to resolve multiple requests to access the audio hardware.

To start playing a DTMF tone, use the CMMFDevSound::PlayDTMFStringL() method:

IMPORT_C void PlayDTMFStringL(const TDesC &aDTMFString);

CMMFDevSound::PlayDTMFStringL() has one parameter, &aDTMFString, the DTMF sequence in a descriptor.

If CMMFDevSound::SetDTMFLengths() is called during play, it takes effect when the next tone is generated.

When an attempt to play DTMF tones has completed, successfully or otherwise, DevSound calls the MDevSoundObserver::ToneFinished() function.

Note: Further calls to CMMFDevSound::PlayDTMFStringL() can be made both before and after the MDevSoundObserver::ToneFinished() callback is received.