Wolfson/CIRRUS LOGIC AUDIO CARD for RASPBERRY PI B+/A+ : power usage.

Question

Hi to all,

I have ordered 2 of these cards and plan to experiment with them to create wireless battery operated sound systems.

Although it should work, eventually, I do miss info on the power needs of this card at this moment.

And I assume when we have got this info listed more of you are hapy to find it. When I am able to answer some myself I will come back and update it

So here is my list :

- Max and nominal power usage.

- Voltage for power input socket.

Answer : It does transport 5 volt fairly unmodified: found a fuse in schematics and a 3.3 Volt regulator for its own circuitry usage

- Confirmation the onboard power socket can power the Raspi B+ and A+

Preliminary answer: the 4 Amp fuse ( F1) should provide some room to power both from J5 = DC_JACK

- Does the board need the on board socket or can it be powered from the Pi itself, with and without the ClassD speaker amp.

- Extra power usage when the ClassD speaker amp is used, for 4 and 8 Ohm speakers.

- sinus or music power output on ClassD speaker amp ( rated 1.5 watt and 2.4 watt on different sheets )

- J5 = DC_JACK : What size ?

One of my ideas is to make it powered/rechargeable though POE. So suggestions to properly extract and regulate that power are welcome too.

However a separeate thread is better.

When I have got my prototypes working I might share my builds here too.

Grtz Marcel

hiassoft · Accepted Answer

Hi Marcel!

Yes, I only checked power on the +5V micro USB input of the Pi. Haven't done any tests with the class D part of the card yet.

If you are still interested you can download my OpenELEC builds from here: http://www.horus.com/~hias/tmp/openelec-wolfson/ - the 20141230 build is the latest one, also checkout the 00README.txt for installation instructions. You can find a lot of background info on the (rather long) thread on the OpenELEC forum: http://openelec.tv/forum/124-raspberry-pi/69870-wolfson-audio-card-support.

Basically I'm just using the Wolfson/Cirrus drivers from the Cirrus Logic git repository on top of the current 3.12 kernel.

so long,

Hias

hiassoft · Answer

I hooked up my RPis to my bench power supply checked the current draw of a RPi B with the Wolfson card and a RPi B+ with the Cirrus card.

For these tests I used my OpenELEC build, powered up and then waited several minutes for background tasks to settle down. At this point the system was idling at the main screen (keep this in mind when comparing absolute current draw values).

I used a fresh OpenELEC installation with default settings, which means the audio device will be closed after 1 minute. Pressing a key results in a click which re-opens the audio device - so I could measure the difference in current draw between the device being idle and when used (the latter also adds a little bit of additional CPU power for the user space program and kernel driver, of course).

I connected a PC monitor to HDMI, a Logitech unifying receiver for my keyboard and hooked up the network cable.

Results for the RPi B:

no audio card, output to HDMI: 429mA (425 when audio device is closed)

Wolfson card installed, but no driver loaded, output to HDMI: 436mA (432 when closed)

Wolfson card installed and used: 480mA (457 when closed)

Results for RPi B+:

no audio card, output to HDMI: 252mA (249 when audio device is closed)

Cirrus Logic card installed, but no driver loaded, output to HDMI: 259mA (256 when closed)

Cirrus Logic card installed and used: 307mA (285 when closed).

Please note that the current draw was jumping around a bit, so these are average values (but they should be within +/- 5mA or so unless I messed up somwhere).

So, basically both cards need some 50-55mA when used and some 30-35mA when idle. But RPi B vs RPi B+ makes a huge difference, especially if you are planning to power the device from batteries.

so long,

Hias