Play audio snippet via nRF51/52

RE: Play audio snippet via nRF51/52

NewtoM — Thu, 03 Oct 2019 22:52:32 GMT

Hi, you can have a look at this PWM audio thread.

RE: Play audio snippet via nRF51/52

JohnBrown — Fri, 06 Nov 2015 10:57:38 GMT

Having taken a quick look at the nRF52 datasheet, I think it would be perfectly viable to do this using the PWM in conjunction with the DMA. In fact, Nordic were demonstrating some drum noises at the nRF51 on tour event last week. If you need any help with this, I'd be happy to look into it, but I don't know what the guidelines are re. soliciting for work on these forums.

RE: Play audio snippet via nRF51/52

Einar Thorsrud — Thu, 05 Nov 2015 14:31:47 GMT

The two you link to are listed as supporting SPI, which is also a perfectly good alternative.

RE: Play audio snippet via nRF51/52

Frits Jan — Thu, 05 Nov 2015 14:24:50 GMT

When looking for a DAC through mouser I could not find i2S anywhere... Can you tell me if one of these support i2S ? eu.mouser.com/.../ or eu.mouser.com/.../DAC8411IDCKT

RE: Play audio snippet via nRF51/52

Einar Thorsrud — Thu, 05 Nov 2015 14:02:46 GMT

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.

RE: Play audio snippet via nRF51/52

Frits Jan — Thu, 05 Nov 2015 13:37:49 GMT

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

RE: Play audio snippet via nRF51/52

JohnBrown — Thu, 05 Nov 2015 13:32:02 GMT

I am not able to answer that in any competent way, except to say that I think you will stand more of a chance if you move up to the nRF52 with its improved performance and DMA capabilities.

I minute of wave file is a lot of data, even if only 8 bits and 8kHz, which is barely "telephone" quality.

RE: Play audio snippet via nRF51/52

Frits Jan — Thu, 05 Nov 2015 13:26:30 GMT

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

RE: Play audio snippet via nRF51/52

Einar Thorsrud — Thu, 05 Nov 2015 13:23:24 GMT

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.

RE: Play audio snippet via nRF51/52

Frits Jan — Thu, 05 Nov 2015 13:21:08 GMT

So the main problem would be timing issues because the SOC is busy with BT handling? In my case I first wanted to get the wav data from the mobile phone onto the device and then play it. But now I am looking into putting all wav files I need on an SD card and then just get a trigger message over BT to play a certain file. Let's say the wav file is 1 minute long, would this be a problem? Or can this run in a separate process so I can still connect to the device via BLE to control it? (I am talking about SPI interface now not PWM).

RE: Play audio snippet via nRF51/52

JohnBrown — Thu, 05 Nov 2015 13:02:54 GMT

I believe it would be possible to play a basic sound on the nRF51 using PWM via the on-chip timers, but not while the soft device is running( I say this having successfully generated DTMF tones via PWM). I also believe I have read stuff recently relating to timeslots being available between SD operations, so I guess if your sound sample was very short, it might be possible.

RE: Play audio snippet via nRF51/52

Frits Jan — Thu, 05 Nov 2015 12:39:18 GMT

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 ?

RE: Play audio snippet via nRF51/52

Einar Thorsrud — Thu, 05 Nov 2015 12:10:50 GMT

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.