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Raspberry Pi and DACs

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Steve Conner

Mon Nov 26 2012, 10:39AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Carbon_rod, what are you suggesting, that the snd_bcm2835 driver conflicts with the USB audio driver? My Wheezy image runs snd_bcm2835 at boot by default, but I could try disabling it. The biggest difference I found was by configuring mpd to use "plughw:1,0" instead of "hw:1,0". This was what finally got rid of the glitches at 44.1kHz. I think the plug device must do some additional buffering and run with lower interrupt latency, maybe because it's part of the kernel.

I heard about the Pi power problems, so the first thing I did was hard-wire a 5V power supply to everything, bypassing the polyfuses, protection diodes and so on.

I disabled the CPU speed stepping, but I haven't tried overclocking it yet. I also used apt-get update and apt-get upgrade, I understand that this gets the latest firmware and drivers, however I didn't try running raspi-config again afterwards. Is this needed to enable a new kernel if "apt-get upgrade" delivered one?

I don't see how the Teensy 3.0 is relevant, can it mount a 1TB USB hard disk, read FAT32 and run mpd? What does an oversized picture of a laser have to do with this thread?

Carbon_Rod

Tue Nov 27 2012, 08:59AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

@Steve
Overclocking practically eliminated the USB delay bugs on some devices, and GPIO18 "PWM mode" dma timer interferes with more than just the audio drivers.

@macona
This link may offer some insights:

Ash Small

Tue Nov 27 2012, 10:59AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve Conner wrote ...

a Â£29 USB DAC from Maplin (order code A14KF)

I think I need to add one of these to my Xmas list

What I'd really like to see is an Android app that lets you connect a smartphone to the Pi's USB interface, and use the keyboard and screen on the phone to program the Pi.

Steve Conner

Tue Nov 27 2012, 11:09AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Carbon_rod: I'll try overclocking it a bit then and report back

What is this "GPIO18 PWM mode" of which you speak, does it have anything to do with the onboard audio output?

Ash: You can do this with SSH, if you can get a SSH client for Android...

Ash Small

Tue Nov 27 2012, 12:14PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve Conner wrote ...

Ash: You can do this with SSH, if you can get a SSH client for Android...

Looks like that will do the job, Steve.

Just add a USB Wi-Fi or Bluetooth unit to the RPi, and you have wireless control of your RPi based multimedia system from your phone

Steve Conner

Tue Nov 27 2012, 01:00PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yup... FWIW, the player application I use, MPD, has dedicated remote control apps for iOS and Android. Off to Maplin to get a USB wi-fi dongle now!

Steve Conner

Wed Jan 16 2013, 12:25PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Update: I now have this working at 24 bits, 96kHz using the USB-I2S module from QNKTC.

Ash Small

Wed Jan 16 2013, 04:00PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve, which of the half a dozen or so WiFi dongles dongles that Maplin sell did you use, and why, as I'm also building something similar?

What specs. should I be looking for?

Steve Conner

Wed Jan 16 2013, 04:51PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I got the "Edimax N150" dongle, because it was the cheapest one that anyone had mentioned on the Raspberry Pi forums.

It has a Realtek chip inside, supported by Raspbian out of the box, by the rtl8192cu kernel module. I easily got it to join my home wi-fi after some tinkering with config files. (There is probably an easy tool to configure it in the GUI, but I'm only using the console for this project.)

The only niggle was that it had a power saving mode that sometimes interrupted incoming traffic. It was fine for streaming radio, but the Windows file sharing and mpod remote control randomly failed to work. I disabled power management using the method below and everything worked fine.

wrote ...
As root, create a file /etc/modprobe.d/8192cu.conf with the following contents:
options 8192cu rtw_power_mgnt=0 rtw_enusbss=0

,8618

The R-Pi is the funnest computer toy I've played with in a long time!

Conundrum

Sat Feb 09 2013, 11:07AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

If you ask me, the RPi model A should have included a second USB port to mount small devices where the network chip used to go.

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