Exploring the new Rasp Pi Model  B+

Pi Plus

© Lead Image © Raspberry Pi Foundation

© Lead Image © Raspberry Pi Foundation

Article from Issue 168/2014
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The brand new Raspberry Pi Model  B+ is solid and tidy, with many clever improvements in detail that make this the best version so far. The desired improvement in performance will have to wait for now.

More than three million Raspberry Pi computers have already been sold. Originally designed to introduce school children to computers, the tiny device has been used as a small server, a media center, an embedded PC in industrial products, and more. The queen of England even honored the project with a visit, and she was amused.

In July, a refurbished Rasp Pi appeared in the form of the Raspberry  Pi Model B+. Although the board for this model is still based on the Broadcom-SoC-BCM2835 with 512MB of main memory, the Raspberry Pi Foundation implemented many improvements in its details (see "Why No Improved Performance?"). Users who need more RAM or gigabit Ethernet will have to wait for another model: According to the Foundation, the next Rasp Pi will appear at the end of 2016 at the earliest.

Why No Improved Performance?

Many fans who use the Rasp Pi as a substitute for a desktop computer or media center dream of having a Rasp Pi with significantly more performance and internal memory, a SATA port, fast gigabit Ethernet, and USB*3.0. The Rasp Pi  B+ doesn't offer any of these. Why does the Raspberry Pi Foundation stay with its old chip set instead of unveiling a fast Rasp Pi? The technology is certainly available.

The Foundation takes great pains to maintain a unified user base and make sure the extensions, code, and optimizations developed thus far, such as those for coding and decoding videos, remain available to all Rasp Pi owners. Many additional software improvements are being developed that would be largely obsolete for a new architecture like Freescale iMX  6. For this reason, the BCM2835-SoC with its VideoCore  IV, which is the brain of the Raspberry  Pi is being kept the same.

Additionally, the Foundation has technical reasons for not improving performance with the current SoC. The ARMv6 architecture used on the Rasp Pi can only handle processing with single-core processors, and the clock speed is limited to a maximum of 1GHz. In theory, the BCM32835-SoC can support up to 1GB of internal memory; however, the necessary structural component is only available with a maximum capacity of 512MB. At an overclocked speed of 1GHz, the Pi already runs at the maximum possible speed and RAM.

Moreover, the SoC has only a single USB 2.0 port that, with the help of the LAN9514 chip, supports four USB connections and a 10/100Mbps Ethernet port. Theoretically, a gigabit LAN adapter can work over USB  2.0 with up to 300Mbps, which is the net average of USB  2.0. However, for NAS applications, the data would have to be sent to the SoC and back through the same bottleneck on a hard drive that is connected through a USB port. This setup would effectively lower the data rate to 100Mbps, which is the rate that the Rasp Pi can already achieve without modifications.

Ultimately, component parts and additional features that make for higher performance, such as an integrated WiFi chip, result in greater costs. Just the licensing fees that would need to be paid to the patent management agency Sisvel for the WiFi technology would cost more than EUR 0.70 (~US$ 0.90) per Raspberry  Pi, whereas the four USB ports allow the user to retrofit for WiFi, Bluetooth, and much more in an easy and cost-effective way.

First Impression

A quick look at the circuit board of the Raspberry  Pi Model  B+ reveals a spiffed up layout. Although the B+ is the same size as the old Model B, it is easier to grab thanks to its rounded edges. Moreover, four holes make it possible to fasten the housing and other accessories more securely. The large capacitor that stuck out so prominently on the Model  B and was easy to break off is gone, thanks to the cleaned up power circuitry, and the USB and Ethernet ports now connect flush with the circuit board. The audio out jack moved to the opposite side of the board behind the Ethernet port, but the connectors for camera and GPIO generally remain in the same places.

The only missing component is the yellow cinch connector for the composite video out, which was removed to make way for a wider GPIO port that now consists of 40  pins instead of the  26 of the previous models. However, it is still possible to coax video footage out of the 3.5mm headphone jack with the help of a suitable adapter or cable. As always, higher quality video is possible by digitally directing the video signal via HDMI to a TV or monitor. The connections for HDMI, audio, and micro-USB are all located on one side so that the positioning of the cables appears a little more orderly (Figure  1).

Figure 1: The most important connections are now located on just two sides of the Raspberry  Pi Model  B+.

Another flaw in previous models that disturbed many users was the slot for the SD card. The memory card stuck out pretty far and was prone to breaking off, along with the mounting on the board. The Model  B+ only accepts the much more compact microSD card in a slot that now latches. As a result, the card disappears completely into the housing, which however makes it more difficult to exchange the card and test a different Rasp Pi distribution.

Starting up the Rasp Pi  B+ is the same as before: You slide the microSD card into the corresponding slot, connect all the cables, and plug the power supply into the electrical outlet. The Model  B+ boots just like the trusty Raspberry  Pi from the very first generation – except for one thing: Because the new USB Ethernet LAN9514 chip that has been added needs new drivers, you need to update older versions of distributions using a Rasp Pi B; otherwise, you will be without a network connection and USB ports.

Stable Current

Apart from the numbers for speed and storage, one of the most important changes made in the Rasp Pi  B+ was in the power supply. Altogether, the new model is much less sensitive to low or fluctuating input voltage and accepts voltage ranging between 4.75 and 5.25V. It is still a good idea, however, to use a high-quality power supply. The Rasp Pi power supply provides the board with an input voltage of 5V. However, different components on the board need 1.8 or 3.3V. Until now, these voltages were taken care of by so called low-drop linear regulators that transformed excess energy into heat.

The Rasp Pi  B+ has noticeably more efficient step-down converters that can decrease the voltage via pulse width modulation and achieve an efficiency of up to 95  percent. As a result, the power consumption of the new model has been lowered on average by 0.5 to 1W.

In addition to the new voltage regulators, a stronger fuse that resets by itself was added. The maximum input current of 2A is double that of the former model. Together with the new voltage regulators, this makes it possible to increase the output voltage of the USB ports to a maximum 1.2A, assuming you have the right power supply and the right configuration (see the box titled "Undercurrent"). This is how the Rasp Pi  B+ accommodates four USB Ports, that can provide electricity to resource-intensive devices like a 2.5-inch hard drive or a DVD drive when neither has its own power supply.

Undercurrent

Via software, the system currently limits the maximum current for the USB ports to 600mA. For the time being, you will need to add the safe_mode_gpio=4 parameter to the /boot/config.txt file to permit the full 1.2A. One of the next firmware updates will change the name of this still hidden switch to max_usb_current=1.

Stabilizing the power supply of the USB port solved some of the well-known problems of the Raspberry  Pi, such as spontaneous system restarts with the insertion of a USB device into a running Raspberry Pi. The B+ has improved protection against these crashes – known as brownouts. Now, it is theoretically possible to hotwire the voltage at the USB port without tripping up the Pi. In the tests we performed, we were able to connect a WiFi adapter, which would have caused a restart in the Model B, without a problem on the B+.

The HDMI output, previously limited to 50mA, can now draw much more power – up to 400mA. In this way, HDMI devices without their own power supply, such as an HDMI to VGA converter, can operate on the new Rasp Pi more easily.

Commercial users and power users will find that the new model does not allow the Rasp Pi to be powered via the USB interface. Thus, the Raspberry Pi Foundation recommends that board developers use the 5V GPIO header pin as a power supply instead of USB back-powering and that they duplicate the corresponding protective circuitry on the Pi board.

LEDs, RUN Header, and Audio

The PWR and ACT LEDs on the Rasp Pi  B+ have migrated to the upper edge of the circuit board under the GPIO. In the future, the PWR LED will serve as an indicator of serious loss in voltage. If the voltage goes under 4.63V, the LED will begin to flicker, or it will go out completely. An unequipped RUN header is located directly beside the ACT LED. It has the same function as the P6 header for the GPIO interface on the model  B Rev 2. A button connected to it reboots the Rasp Pi without the need for manually cutting the power. It can also be used to wake up the machine after it has powered down. Two of the three LAN LEDS have been placed directly in the Ethernet jack instead of on the circuit board.

The audio jack referred to earlier in the article sits next to the network connection and has become much more compact than ever before, although with the video output it contains an additional pin (Figure  2).

Figure 2: Sound and video signals can be sent out over the four-pin, 3.5mm plug connector.

Standard 3.5mm headphone plugs used for headphones or cinch cables still fit in the jack. A plug connects the video output with ground. Apple uses a similar plug assignment for video iPods, with left and right reversed. As a result, you will find many low-priced adapters available for purchase.

Previously, if you wanted to get good sound from the Rasp Pi analog audio output, it was necessary to rely on a USB sound card because of the shaky power supply. Now with the B+, a separate currency regulator provides more consistency in the flow of electrical power and, consequently, better sound quality. The output impedance has been reduced significantly and the maximum signal level increased. Improvements in relevant sound production software should soon be forthcoming. According to the Raspberry Pi Foundation, the VideoCore IV DSP engine (VPU) still has leeway for improvement.

In our comparisons, we found that the analog output of the B+ is more detailed, somewhat louder, and in general more pleasant than the Model  B. However, when the audio output simply runs with no music playback, you can still hear a noise. Also, the Rasp Pi still lacks a microphone, or even a mic input. Thanks to the four USB ports, however, it is possible to retrofit a mic via USB.

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