Play audio snippet via nRF51/52

[Frits Jan]

I am working on a device which also needs to give audio feedback to the user. The app on the mobile phone needs to send a wav (or similar) file (mono, speech) to the device and the device needs to play it through a small speaker.

Is this possible with the nRF51/52 and if so can you direct me in what is needed for it to get it working (DAC, amplifier, how to transfer the data, (external)buffer/memory needed, etc?)

Thanks in advance!

[Einar Thorsrud]

We do not have any recommendations when it come to audio playback. This is not a common use-case for the nRF51. However there are several thread on DevZone that ask similar questions, such as this one.

I think you have already listed the main components you need:

• DAC
• Amplifier
• External memory

The nRF52 has I2S, which may be the best option for communicating with the DAC, depending on which DAC you choose. You should use EasyDMA so that you do not experience dropouts of the audio when the CPU is busy doing something else. I2C and SPI are other alternatives.

A alternative for very basic sounds can be to use the PWM peripheral on the nRF52.

[Frits Jan]

Thank you for your answer. I came across this site: developer.mbed.org/.../ Where there is an example of playing a .wav file from an SD via DAC output and a transistor (or amp) to a speaker. Is something like this possible with the nRF51 (it doesn not have DAC output right, so I need an external DAC)? And what could be the drawbacks?

What will be the advantage of i2S on the nRF52 versus i2C or SPI on the nRF51 ?

[Einar Thorsrud]

It should be possible on the nRF51, using a low sampling rate. The details depend on the DAC, how you communicate with it, the sample rate, the bits per sample etc. Moreover, unless you can transfer data to the DAC using DMA you will get gaps in the sound. You can also try to use PWM as described by JohnBrown on the nRF51. On the nRF52 you have more options and EasyDMA on most relevant peripherals regardless of going with an external DAC or the internal PWM peripheral. I think you need to specify the level of quality etc. you need (sampling rate, bits per sample) and duration of the sound clip in order to say anything about advantages/disadvantages of the various solutions.

[Frits Jan]

Lets say 22kHz and 12-16bit. Speech with a little bit of background music files. snippets of audio of say max 30 seconds long

[Frits Jan]

My guess was that when it could be done on an 8bit micro like arduino, the nRF51/52 would cope with this easily. So something similar like this: learn.adafruit.com/adafruit-wave-shield-audio-shield-for-arduino

[Einar Thorsrud]

I think you should be able to do this. If the data is stored on a SD card you could use the SPIM peripheral of nRF52 to read the data and write it to the DAC over I2S using the I2S peripheral. Both the SPIM and I2S peripherals of the nRF52 support EasyDMA.