Raspberry Pi version B+

Previously I wrote:

I had ordered a BBB for no other reason that it’s better looking than the Rpi 🙂

Well, no longer. I ordered the new version B+ because it is as good looking as the BeagleBone Black 🙂

Not really. The reason is because that there is a lot, lot more community development in the Pi than the Beagle. In fact if we just look at shipments, the Raspberry Pi sells almost 20 times the amount of BeableBone Black (over 3.8 million [link] vs 200,000 devices [link]). This is a huge advantage in the popularity front.

I had been a fan of the BeagleBone board [link] mainly because it is a higher performance board and had local storage. In addition (by design or by accident) the audio master clock uses an on-board 24.576 MHz clock from which it derives the frequencies for 48KHz sample rate material with integer division. There is also the capability of receiving the master clock from external sources and thus it is possible to feed it a higher quality 24.576 MHz and 22.5792 MHz clocks. There has been a clock board (and corresponding drivers) in the works since early this year, but nothing available yet as of this writing [link]

In contrast, there has been a much larger development effort in the RPi front as testified by the numerous I2S DAC boards that have become commercially available. Many of these companies are dedicated to building audio solutions first for the Raspberry Pi and then possible for other embedded platforms.

Here is a list of DAC boards available for the Raspberry Pi (versus none for the BeagleBone Black as of this writing)

COMPANY	PRODUCT	PRICE	DAC CHIP	COMMENTS
G2 Labs	BerryNOS 1543 RED	$125	Philips TDA1543	Balanced design, discrete output stage, power supply
	BerryNOS mini	$60	Philips TDA1543	Balanced design, discrete output stage
HIFIBerry	HiFiBerry DAC	€25	TI PCM5102A
	HiFiBerry DAC+	€30	TI PCM5122	DAC volume control
IQAudio	PiDAC	$38	TI PCM5122	DAC volume control
	PiDAC+	$42	TI PCM5122	DAC volume control, headphone amp
Saparel	RaspiPlay3	$40	TI PCM5102A	From Serbia
	RaspiPlay4 [link]	TBD	TI PCM5122	DAC volume control, IR remote
Audiophonics	I-Sabre DAC	€25	ESS ES9023
	I-Sabre DAC+	€43	ESS ES9023
Element 14	Wolfson Audio Card	$35	Wolfson WM5102	Available through resellers. WM5102 is a complete audio system. The board implements line-in, line-out, speaker and headphone output and mic input. The board also includes a WM8804 providing SPDIF input and output, a digital microphone and expansion header for other Wolfson devices
TekDevice	DACBerry2+	$45	TI PCM5102A
	DACBerry3+	$51	ESS ES9023
HIFImeDIY	ES9023 DAC	$19	ESS ES9023	Lowest price!
DurioSound	DurioSound	$45	TI PCM5102A	Has ultra low noise regulator (TPS7a47)
	DurioSound Pro	$70	TI PCM5102A	Has ultra low noise regulator (TPS7a47) and Local Power Supply

Notes:

1. Notice that the DAC chips used are the ones that can cope without a Master Clock. RPi I2S does not Master Clock, so the DACs synch on bitclock and generate their own master clock.
2. Products using PCM 5122 can use the DAC’s internal volume control and therefore can be connected directly to an amplifier.
3. There are companies such as diyinhk and curryman that are not listed because they do not specifically make DAC boards that conform to the RPi footprint but are fully functional as I2S DACs. Any I2S DAC that does not require master clock will work.

My Favorite ones are the HIFIBerry DAC+ and the IQAudio PiDAC+, both based on the PCM 5122 with “hardware” volume control (meaning using the volume control in the DAC itself)

[link]

[link]

WHAT IS NEW IN THE B+

In the two years since we launched the current Raspberry Pi Model B, we’ve often talked about our intention to do one more hardware revision to incorporate the numerous small improvements people have been asking for. This isn’t a “Raspberry Pi 2″, but rather the final evolution of the original Raspberry Pi. Today, I’m very pleased to be able to announce the immediate availability, at $35 – it’s still the same price, of what we’re calling the Raspberry Pi Model B+. [link]

There are a million reviews on the Raspberry Pi. Here is one more but with a slant towards diyaudio…

New Layout (and more I/O pins)

Notice that the I2S pins are right next to a GND pin. This is particularly good as you can easily use twisted pairs (for noise immunity) when connecting to a DAC

List of integrated circuits [link]

Label	Device	Description
U1	BCM2835	SoC comprising ARM Processing core and Video Core. Data Sheet
U2	LAN9514	4 USB 2.0 Hub and 10/100 Ethernet controller. Data Sheet
U3	PAM2306AYPKE	Dual DC-DC Switching converter. Data Sheet
U4	APX803-46SAG	Brownout detector (reset generator)  Data Sheet
U5	AP7115-25SEG	150 mA Linear Regulator. 50 uV noise (Video DAC)  Data Sheet
U6	N.U.
U7	N.U.
U8	ESD5384	ESD protection for HDMI. Data Sheet
U9	AP2331W	Current limited switch (for HDMI hot plug) Data Sheet
U10	AP7115-25SEG	150 mA Linear Regulator. 50 uV noise. (PWM Audio Driver supply) Data Sheet
U11	NC7WZ16	Ultra High Speed dual buffer. (PWM Driver) Data Sheet
U12	N.U.
U13	AP2553W6	USB current limited power switch (for hot plug). Data Sheet
U14	DMMT5401	Matched PNP transistors. Data Sheet

Board schematic here: [link]

The audio jack is also a composite AV jack

More USB Ports

New USB/Network Chip (to support the 4 USB ports)

The USB powerchain has a proper limiting switch and will not brown out the board if USB devices are plugged in when powered (or even if they try to take too much current or there is a fault like a power short). Default allowed USB current across 4 ports is 600mA, but can be increased to 1.2A via a config.txt parameter if a good quality 2A PSU is used. I have tried a few different USB hard disks and they all power fine directly from the Pi at the 1.2A setting. [link]

To increase power to 1.2A you add the following line in /boot/config.txt[link]


• max_usb_current=1 (newer software)

• safe_mode_gpio=4 (older software)

The 5V for the USB ports is provided directly by the 5V of the input supply. The schematic below shows the 5V sourced from Power In. There is a 2A fuse a diode-like low-drop polarity protection circuit and an over-voltage zener.

Therefore a better quality power supply is required. Here is an excellent post on choosing and evaluating 5V charger/supply [link]

I like the Orico DCX-2U. It has two USB outputs: 1×2.4A, 1×1.5A. The 2.4A output is plenty for a “fully loaded” RPi

High Efficiency Switching Supply (power consumption is reduced by between 0.5W and 1W)

The DC-DC Switching supply is the PAM2306AYPKE. This device supplies the 3.3v and 1.8v supplies. The switching frequency is 1.5MHz (which can easily removed by the LC filters on the outputs).

MicroSD Card Slot

There are many theories as to why the SD card was replaced with the micro SD card. I think it is probably lower cost.

BETTER ANALOG AUDIO

According to the people from Raspberry Pi, the audio in the B+ model has been improved. The audio circuit (AUDIO out) incorporates a dedicated low-noise power supply (the input to this power supply is the external 5V supply). According to this comment [link]:

The B+ does not use use a switching regulator for its PWM driver, that would indeed be a bad design choice, instead it uses the AP7115-25SEG [link] low drop regulator with high power supply rejection ratio. It creates a noise free 2.5V for the NC7WZ16 PWM driver, the output of which is attenuated and filtered with two 100 Ohm resistors, and a 100 nF capacitor, so the output is 50 Ohm, and can reach 1.25Volt p/p.

U10 is the linear regulator and U11 is the “PWM Driver”

Whether this audio is “better” or not, it does not concern us. Take a look at this post [link].

WHAT’S THE SAME?

Same SoC (Same ARM processor and GPU and 512MB of RAM)

Unlike the BeagleBone Black, there is no local memory for storage. The s/w runs out of the microSD card.

Same external 19.2 MHz crystal