Tag Archives: Raspberry Pi

Orange Pi 2G-IoT Challenges the Raspberry Pi

If you are looking for an alternative for the ubiquitous Raspberry Pi (RBPi) or one of its siblings, give the Orange Pi 2G-IoT a second look. The Shenzhen-based maker of the Orange Pi developer board has made this one to rival the RBPiZW, the RBPi Zero W.

The Orange Pi 2G-IoT is a new design for a single board computer, available for sale of AliExpress. The device can run Android, Debian, Ubuntu, or Raspbian. It gives builders a 2G antenna to run applications for the Internet of Things, and that is where it gets the IoT in the name, while offering wireless LAN and Bluetooth for the same price as that of the RBPiWZ.

Featuring a 1 GHz ARM Cortex-A5 processor running at 32 bits, the Orange Pi 2G-IoT has a 256 MB RAM, and GC860, a Vivante graphics processor. The board supports 802.11 b/g/n Wi-Fi, Bluetooth 2.1, and 40-pin GPIO connector that matches the RBPi GPIO layout. Additional features include audio and video outputs and inputs, and USB 2.0 ports. There is a slot where you can insert a SIM card, while the 2G antenna supports GPRS/GSM data connections. The only two points of difference with the RBPiZW is it has double the RAM, that is 512 MB, while the Orange Pi 2G-IoT has 500 MB of on-board NAND flash to go along with the SD card slot.

With the Orange Pi 2G-IoT, you do not get a Display port, HDMI port or a VGA port. However, an LCD connector is present, where you can connect an external screen.

However, as the Orange Pi 2G-IoT is still new in the market, anyone who plans to use these devices must proceed with caution on two points. One, check if there is software support for the devices. The RBPiZW is a known entity and has a huge array of operating systems and software to run on it.

Second, those buying the board should check if there are carriers still supporting 2G. For instance, in the US, AT&T and many other carriers have killed off their 2G network, and many are planning to do so very soon. The situation is very similar in the UK. However, there are still some in other parts of the world who continue to support 2G and may do so for years to come.

These ultra-small single board computers offer a lot of options, the list continuing to grow at the lowest prices. After considering the shipping costs, we can call these the sub-$20 boards. This includes the RBPIZW that has the Wi-Fi and Bluetooth, the Orange Pi Zero, and now the Orange Pi 2G-IoT.

Even with all the impressive features at below $10, especially the addition of GPRS/GSM, the Orange Pi 2G-IoT is not likely to kill the sales of RBPiZW. This is mainly because of the community support the RBPiZW currently enjoys. Of course, the Orange Pis are great little computers, but if you run into a problem with them, you are likely to find less support online, as compared to what you can expect from the huge online community supporting RBPiZW.

RS485 & Raspberry Pi: Monitoring Power

Commercial data centers, lighting controls, utility rooms for buildings, and others need to keep a tab on their power consumption. The normal way to do this is by using electronic voltage meters and multi-branch current monitoring circuits. Vytas Sinkevicius wants to monitor power consumption using the ubiquitous single board computer, the Raspberry Pi (RBPi) as the main controller and the RS485 interface in a Branch Current Monitor (BCM) system.

The heart of the power monitoring system is an RBPi 3. Other parts the system uses are a Pi-SPi-RS485 Interface, a VP-EC-BCM Interface, a breakout PCB for an 18-Channel Current Sense Transformer, and a few Current Sense Transformers. Vytas will be writing the software in C, using the Geany compiler.

Electrical engineers use two types of current sense transformers for measuring current. The first type has a continuous hollow core, with the wire carrying the current passing through the hollow of the core. This type of current transformer is suitable for new constructions and requires the main power to be turned off for installations. The breaker wire has to be removed and re-connected after the current transformer is attached.

The second type of current transformer has a split hollow core, where one-half of the core may be separated from the other. Split cores are ideal for applications where the power wiring to the breakers cannot be switched off. By separating the top half of the core, the breaker wire can be placed in the hollow of the lower part, and the top half of the core replaced thereafter. Vytas is using a split-core current transformer, model type CR3110-3000, and CR Magnetics manufacture it.

The Pi-SPi-RS485 Interface provides power to the VP-EC-BCM Interface and communicates with the RBPi. As the RBPi and Pi-SPi-RS485 combination uses the Modbus RTU and RS485 protocols, they can be located as far as 4000 feet away from the actual area where power is being monitored.

The Pi-SPi-RS485 is a perfect fit for the RBPi3, as its ports match the GPIO port on the RBPi3. Moreover, as it duplicates the GPIO expansion port on the other sides of the Pi-SPi-RS485 module, additional modules are easy to add. You can fit the module directly on the back on an RBPi3, or use optional mounting hardware to connect and keep them alongside. All RS485 signals are duplicated on terminal blocks on the board, and on the RJ45 connectors as well.

Each RS485 module has its own power input (9-24 VDC) for powering remote transmitters, and its LDO regulator operating from the 5 VDC bus provides the 3.3 VDC. Therefore, this does not load the 3.3 VDC bus of the RBPi. There are on-board LED indicators for indicating the status of power and RS485 signals. Termination resistors can be selectively switched in using jumper settings provided. The module provides power to the VP-EC-BCM Interface over a CAT5e cable via the dual RJ45 connectors.

The VP-EC-BCM Interface made by VP Process Inc. does the actual power monitoring. This is a converter unit for current sense transformer with 36 channels. It has a 3-kVAC isolation between the primary circuits and the Power/RS485 Interface.

Orange Pi Prime – Another Rival for the Raspberry Pi 3

There is another Orange Pi among the branches of the highly productive Orange Pi tree belonging to Shenzhen Xunlong. This is the Orange Pi Prime—another rival to the most popular Raspberry Pi 3 (RBPi3). According to the year-end Linux hacker SBC roundup, half a dozen individual Orange Pi models were already existing, and if all the new variants are to be included, that number almost doubles. Proceeding at this rate, the company’s engineers will have checked out almost all possible combinations possible with size, RAM, I/O, and hacker board layout for an Allwinner processor.

Similar to the recent releases of Orange Pi Win and its sibling, the Orange Pi Win Plus, which are built on the quad-core, Cortex-A53 Allwinner SoC, the $30 Orange Pi Prime is also a fully open source SBC. In addition, similar to the more minimalistic Orange Pi PC 2 and its sibling the Orange Pi Plus H5, the Prime tab means they are using the newer SoC, the Allwinner H5. However, compared to the Allwinner A64 of the Win boards, the Orange Pi Prime has the more powerful Mali-450 MP2 graphics processor. The H5 processors typically run at clocks of 1.2 GHz.

Whenever a Linux capable hacker board surfaces in the market, people refer to it as an RBPi competitor, which could be erroneous—considering their features, size, and prices vary considerably. However, in the case of the Orange Pi Win and the Orange Pi Prime boards, including some boards such as the Odroid-C2 and NanoPi A64, the comparison with the RBPi3 is downright correct, given the close approximation of their feature set, performance, and price. Even their 40-pin expansion connector is pin compatible to that of the RBPi3.

The Orange Pi Prime is very similar to the Orange Pi Win board. Both have the generous 2 GB RAM, same as that available on the Odroid-C2. Also, just as the Orange Pi Win does, the Prime too has a micro SD card slot, Bluetooth, 802.11b/g/n Wi-Fi, a GbE port, HDMI port, AV, microphone inputs, MIPI-CSI, and a 3.5 mm audio output.

Apart from the above, there are other common features as well. These include the 40-pin connector, debug, GPIO, IR interface, and an operating temperature range of -10 to 65°C. The Prime has a footprint of 98 x 60 mm, which is only slightly larger than the 93 x 60 mm footprint of the Win. Among the differences with the Win, the Prime has only three USB 2.0 host ports, and does not have a battery connector, optional eMMC, or PMIC.

Unlike the Win boards, the Prime will not be supporting Windows 10 IoT in the future. The Linux distributions for the Prime are also somewhat different. They include Android 4.4, Ubuntu Desktop, Debian Desktop, and Arch Server.

The hardware specifications for the Orange Pi Prime include the Allwinner H5 processor, which is a 4x Cortex-A53 and an ARM Mali-450 MP2 GPU. The board runs on a 2 GB DDR3 SDRAM, has 2 MB NOR flash memory, and a micro SD slot with up to a maximum capacity of 64 GB.

Is there a 64-bit Raspberry Pi?

Although the arrival of the Raspberry Pi 3 (RBPi3) heralded a huge speed boost for the Linux hacker board, this $35, wireless-enabled single board computer did not signal a switch over to 64-bit ARM computing. Even though the hardware, following so many other SBCs at the time, was 64 bits, the default Linux distribution from the Raspberry Pi Foundation is still 32-bit.

Eventually, there will be a changeover to 64-bit ARM firmware, as the technology offers significant improvements in performance. More power-efficient chips, such as the 64-bit x86 are also piling on the pressure. However, the Raspberry Pi Foundation is still not committing itself beyond considering a change in the coming months to the 64-bit for the default Raspbian distribution as the reworking of the code required for the changeover is going to be extensive.

The RBPi3 has advanced to the new quad-core of Cortex A53 BCM2837 SoC from Broadcom. Architecturally, this SoC is quite similar to the BCM2836 that the predecessor RBPi2 uses—the quad-core Cortex A7. The Pi Foundation claims that even while operating in 32-bits, the RBPI3 delivers more than 50% better performance than delivered by the RBPi2. This is because of two improvements, one due to the superior architecture of the Cortex A-53, and the other due to the higher clock rate of 1.2 GHz of the RBPi3, as compared to that of 900 MHz of the RBPi2.

While comparing the RBPi3 with the RBPi2, we find the BCM2837 on the RBPi3 is paired with the same VideoCore IV GPU from Broadcom, similar to that in the RBPi2. However, in the RBPi3, the GPU is clocked at a higher rate of 400 MHz. That precludes any video performance at 4K, deep learning projects, or any high-end VR from the RBPi3. On the other hand, the Odroid-C2, being equipped with a Mali-450 GPU, supports 4K video decoding.

Eben Upton, the CEO for the Foundation’s commercial arm, the Raspberry Pi Trading, has explained this. According to Upton, the VideoCore IV 3D is the only 3-D graphics core for the ARM-based SoCs that has been documented publicly and the Foundation wants to make the RBPi more open over time.

Apart from the new SoC, the RBPi3 has also added a wireless chip from Broadcom, the BCM43438, and this enables it with 2.4 GHz, 802.11n Wi-Fi, and Bluetooth 4.1 BLE. With this addition, the RBPi3 steals a march over the Odroid-C2, which lacks wireless, operates on a Cortex-53 Amlogic S905 SoC, and costs $5 more.

Whether to have wireless onboard, or to let users select their own wireless options via Ethernet or USB adapters, has been the subject of an intense debate. As earlier, cost was the main consideration, and the deciding factor came from the dropping prices of wireless chips. Further, the single antenna of the Broadcom chip can be soldered directly onto the board, rather than be used as a module.

Other than the slight shift in the placement of the LED, the new processor, and the wireless capability, the RBPi3 is identical to its predecessor, the RBPi2. They share the same dimensions, amount of RAM, and the 40-pin expansion connector.

Extending IoT with the Raspberry Pi

Recently, the Raspberry Foundation has updated its embedded Compute Module with a faster ARM processor. This will help developers and businesses build new IoT devices. The new Compute Module 3 (CM3) comes with a powerful new option and embedded compute capabilities for device makers interested in the Internet of Things (IoT).

Although not to be confused with the Single Board Computer, the Raspberry Pi (RBPi), with which the CM3 also shared the latest update, is a tiny form-factor ARM-powered SBC originally developed to help both kids and adults learn computer programming.

Launched with the same form factor as that of the RBPi, the CM3 was specifically targeted at business and industrial users. While the RBPi is a completely standalone device, the CM3, on the other hand, is a module intended for plugging into a separate Printed Circuit Board. The primary aim of the Compute Module is to let vendors and developers develop customized products quickly.

The new CM3, like the RBPi3, also uses the same Broadcom system-on-chip (SoC), the ARM BCM2837. The ARM Cortex A53 design forms the base for the SoC BCM2837, which is a 1.2 GHz, quad-core chip running on 64 bits. As a bonus, the standard CM3 has an on-module eMMC flash memory of 4 GB.

Other than the standard CM3, the Raspberry Pi Foundation also has a CM3L or Compute Module 3 Lite version. With the CM3L, users can wire up their choice of an SD card interface or eMMC memory. While the CM3L also comes with the same BCM2837 SoC, the on-board RAM is still restricted to 1 GB only.

Along with the CM3 and the CM3L, the Raspberry Pi Foundation is also releasing the new Compute Module IO Board V3 (CMIO3). This will provide developers with a starter breakout board to which they can connect their Compute Module.

The CMIO3 offers designers a starting template for designing with the Compute Module, providing them with a quick method to experiment with the hardware and to build and test a system. Once the experiment succeeds, they can proceed with the expense of fabricating a custom board. The CMIO3 also provides the necessary USB and HDMI connectors to make up the entire system that boots up and runs the Raspbian OS, or any other OS you select.

Although the Raspberry Pi Foundation has only recently released new Command Modules, next generation large-format displays based on the modules are already available from the consumer electronics vendor NEC, as they had early access to them.

The idea behind the Compute Modules is to provide a cost-effective and easy route to making customized products using the hardware and software platforms of the RBPi. The modules provided the team in the garage the same technology that the big guys already had. The Module takes care of the complexity of routing the core power supply, the high-speed RAM interface, and the processor pins, while allowing a simple carrier board provide the basics in terms of form factor and external interfaces. The form factor of the module follows that of the inexpensive, easily available, standard DDR2 SODIMM.

A Raspberry Pi DAC for the Audiophiles

Raspberry Pi (RBPi) users have several choices for using Digital to Analog Converters (DACs) when listening to music. Two of the latest DACs available in the market are discussed here. One of them is the DragonFly series from AudioQuest and the other is i-Sabre from Audiophonics. Both offer stronger and more meaningful connections between music enthusiasts and the albums, songs, videos, and artists they adore.

DragonFly USB DAC, Preamp, and Headphone Amplifier

The multi-award-winning DragonFly USB DAC, preamp, and headphone amplifier from AudioQuest is a popular product that effectively bridges the gap between extreme audiophiles and mainstream music lovers.

Plugging into the USB port of a computer, including single board computers such as the RBPi, the DragonFly bypasses the compromised audio circuitry of the computer to deliver clearer, cleaner, more natural sounding music and sound to headphones, powered speakers, and complete audio systems.

Two versions of the DragonFly are available—the Black, and a higher-performing Red version. Both versions offer 32-bit digital performance using the Microchip PIC32MX micro-controller, which draws 77% less current from what the previous micro-controllers did that AudioQuest was using. Both versions offer naturally detailed, more authentic sound thanks to the improved ESS Sabre DAC chips working at 32-bits, and using minimum-phase filtering. The DragonFly Red has the latest ESS headphone amplifier and a bit-perfect digital volume control incorporated on the 9016 DAC chip. This ensures maximum fidelity, improved signal-to-noise ratio, and high dynamic contrast.

Both versions of the DragonFly generate enough power to drive all preamplifier input circuits successfully, and they are compatible with a wide range of efficient headphones. While the Black outputs 1.2 Volts, the Red has a 2.1 Volt output and is further compatible with a wider range of power-hungry, low-efficiency models.

The iSabre ES9023

This product from Audiophonics is an I2S DAC, suitable for RBPi model 2, and it has a high precision clock onboard. It produces better quality sound as compared to the DragonFly USB DAC. The clarity is very good and the iSabre gives offers good stereo placement along with detailed high frequency reproduction. This makes the sound very transparent and optimally realistic.

The iSabre ES9023 ideally transforms the RBPi A+, B+, or 2.0 into a high-definition music file player. The converter offers a high value for money and has direct analog outputs on high-quality headers.

The converter has ultra-low noise regulators, OS-CON capacitors, which gives the DAC its musical sound and rich mono details. The HAT format allows direct access to the RBPi GPIO pins, but users have the additional choice to use I2S inputs or the USB interface.

To use the DAC, you may need to install the Hifiberry or the Hifiberry+ driver on the RBPi. The appropriate I2S card will show up on the list of audio devices in the Playback menu.

The cornerstone of a top-quality audio system depends on the accurate conversion of music and sound from the digital to the analog world. The two DACs described above do this conversion admirably. An oversampling process eliminates all the clocking inconsistencies or jitter commonly found in typical digital-to-analog conversions.

Wordery Uses the Raspberry Pi for Book-Wrangling

Among the mass of technologically advanced stuff done with the popular single board computers, the Raspberry Pi (RBPi) has also been helping booksellers. At Wordery, an online bookshop, Jeff Podolski, an IT and network technician, is using the RBPi at their warehouse.

Wordery has over 10 million book titles in their list, including several on RBPi. Over the last few years, they have been working on improving their productivity and customer service drive. For their sorting and distribution operation, they have taken up a greater automation. This is allowing them to track packed items and offer interactive feedback to their staff. For this, they needed PCs on the desks they use for packing and mailing. However, a PC with a screen and barcode scanner would take up considerable space on the desk and consume a lot of power. Therefore, their IT team had the brainwave of using RBPis instead.

Jeff and his team conducted initial tests using an RBPi and a standard PC. They settled on using a setup with the 7-inch official LCD screen and case for the RBPi, and used a USB barcode scanner. This setup saved more than four-fifths of the space a PC would have used up on the desk, while using substantially less power.

However, an RBPi with screen and scanner, left unsecured on the desk, was likely to be knocked and bumped by items being packed and possibly smashed on the warehouse floor. This led Jeff to use a tablet-mounting arm, originally designed for wheelchairs. He clamped the arm to a table, and attached a backboard to the bracket meant to hold the tablet.

Making use of the rear mounting screw holes, Jeff was able to attach the RBPi and screen to the bracket. By routing and tidying the cable layout, Jeff and his team had a low power, small, easily movable interactive terminal, which all the staff in the warehouse could use.

The success of the project led to an installation of over 40 of these terminals in the warehouse, with benefits clearly visible. The warehouse has since processed record volumes using the terminals. They have improved on the previous year’s performance by 11%. Since they set up the RBPi terminals, the warehouse has been handling additional volumes, and packing productivity has increased by 30%. According to Jeff, the resounding success of the RBPi terminals has encouraged their use elsewhere in the building also, further reducing their equipment costs and power consumption.

With the RBPi community and the team at ModMyPi helping with the sourcing of the kit and cables in large volumes, Jeff’s team did a great job of modifying the tablet arm to make it fit another purpose. The RBPi Thin Client Project made the simple configurable thin client for project, while Martin Kirst helped to make the terminal emulator screens more readable and added new functionality to the units. By making the interaction wireless, the terminals can be moved to places where they are currently needed.

This project proves the RBPi can be used for making automation cheaper, more accessible, and much more flexible in an industrial setting.

Networked Storage with the Raspberry Pi

With memory going cheap, almost everyone has a plethora of high-capacity hard disks lying around. Networking them makes it super convenient for use, as you can access files from any computer, even if they are remote. However, this can be an expensive proposition, unless you are using a convenient single board computer such as the Raspberry Pi (RBPi).

The RBPi can be used to create a very cheap NAS setup with a few hard drives connected to a network and accessible from anywhere. Apart from the hard drive itself, you will need an RBPi. Although models 1 and 2 may work just fine, they may not be able to provide enough power to operate some hard disk drives. In this context, the RBPi3 offers better support, but you will still be limited to 100 Mbps via its Ethernet, and USB 2.0. However, using a powered USB hub for powering the external hard drives may be another alternative.

You will need to install the operating system for the RBPi on to an 8 GB micro SD card. Use the OpenMediaVault OS, by downloading it from here. Format the SD card to FAT32, and write the image of the downloaded and extracted OS to the SD card.

Now connect peripherals to the RBPi and its power supply. Initially, you will need a keyboard, a monitor, and a local network connection via Ethernet. Power up the RBPi and allow it to complete the initial boot process.

Once completed, you can use the default web interface credentials to sign in—use admin as the username and openmediavault as the password. The login will give you the IP address of the RBPi, and for subsequent log-ins, you will no longer need the monitor and keyboard connected to the RBPi.

At this stage, you can connect the storage devices to the RBPi. On another computer, on the same network, open a web browser and enter the IP address of the RBPi. Enter the same credentials in the web interface that appears, and you will reach the web interface for the OpenMediaVault. This will bring you to the navigation menu.

To get your NAS online, you first need to mount the external drives. In the navigation menu, clicking on File Systems under Storage will allow you to locate your storage drives under the Devices column. Click on one drive to select it and click Mount. Now click Apply to confirm the action. Repeat the steps to mount additional drives.

You will also need to create a shared folder to allow other devices on the network to access the drives. Finally, to allow an external computer on the network share the folders and drives, you must enable SMB/CIFS from Services in the navigation menu. Next, click on the Shares tab and Add the created folders one by one. For each, click Save.

Now that the NAS is up and running, you can access the drives from another computer by mapping them. To access them, the RBPi will ask for login credentials. By default, these are pi as the username and raspberry for the password.

Raspberry Pi to Displace the Business PC

For a business establishment, maintaining PCs for each of their several hundred employees can be an expensive proposition. It is much simpler and cheaper to have a centralized workstation with several thin clients connecting to it. The ubiquitous single board computer, the Raspberry Pi (RBPi) is a suitable component for use as such a thin client.

As the low cost of the Raspberry Pi makes it a very attractive proposition for use as a thin client computer, Citrix is offering an HDX Ready Pi to replace the regular desktop PC. They are coupling the RBPi with virtual desktops such as the Citrix XenDesktop and the XenApp virtual apps. The combination is an ideal replacement for the traditional desktop PC and its IT refresh cycle.

At the heart of the project are two thin client operating systems, ThinLinX and TLXOS, based on Raspbian, the default OS for the Raspberry Pi. These provide the image for the RBPi and include the client and management software. Citrix is making use of these to instill an HDX SoC Receiver SDK within the securely locked-down Linux OS and the SDK provides full device management for updating firmware, remote configuration, and DHCP, making the RBPi a completely plug-n-play device.

Available fully assembled and ready-to-order from Citrix partners ViewSonic and Micro Center, the HDX Ready Pi thin-clients come preloaded with all the necessary software, power supply, flash storage, VESA mount option, all packaged in a production case. Any IT administrator can deploy these thin-clients in a matter of seconds.

Apart from being just a cheap PC alternative, these RBPI thin-clients offer businesses several new business paradigms. For instance, businesses now need not pay a premium for security and management of all their PCs, and they can expand their number of users to cover the entire organization.

The Citrix HDX Ready Pi is easy to set up. As it is small, distribution is simplified and employees can connect it up to an available display and be productive in a matter of minutes. IT can configure the management software, recognize the HDX Ready Pi in the network, take control of it, and point it automatically to the correct Citrix Storefront server. The user can then run any instant virtual app with desktop access.

As the RBPi thin-clients have no hard disks to fail, there is also no data and time wasted in diagnosing device problems. This eliminates all desk-side support, as any issue can be solved simply by swapping the device.

The low cost of thin-clients also eliminates treating them as trackable financial assets. Businesses can rather consider the Citrix HDX Ready Pi as non-capitalized office expenses, providing a compelling situation to virtualize remote branch offices all over the world.

As there is no provision to store or cache corporate data, businesses can safely distribute the HDX Ready Pi among employees for occasionally working from home over Wi-Fi or for teleworking. Employees can take the device home and use it safely for remote access.

Although the Citrix HDX Ready Pi has a Kensington lock slot, its low cost makes physical security almost a non-issue. Moreover, as the device is purpose-built for Citrix, it can be safely used as a pervasive computing device in an office campus or in public spaces.

Volumio for the Raspberry Pi

When you search for a networked stand-alone audio player with a touch screen, most likely chances are you will only find big consumer grade amplifiers. Those with network support may not have a touch screen or else may be very expensive. Most disappointing will be those having an issue with space and mobility. The best way out of this dilemma is to build one with the famous single board computer, the Raspberry Pi (RBPi).

You must start with an application that works on the RBPi. You can already find good quality DACs on the market. The makers of the application Volumio have used PCM1794A, the DAC from Texas Instruments with good results. As this is a 24-bit device, it can handle sample rates up to 200 KHz, and offers an 8x oversampling filter built-in.

The PCM1794A requires two voltages for proper functioning. It needs the 3.3 V for its digital part and the 5 V for its analog part. Although it seems possible to use the two voltages available on the GPIO expansion connector, the noise present on these voltages precludes their use for the DAC. Another possibility would be use the power supply for the DAC to power the RBPi. However, that is also not advisable, as this would mean degrading the power supply of the DAC. Therefore, the two devices need two distinctly different DC adapters.

For the I/V converter, another voltage is necessary and this has to be a negative voltage. The designers derived the negative voltage using the LM27761 IC, a special switched capacitor low-noise regulated voltage inverter. The IC is extremely small, only 2 x 2 mm, and operates at 2 MHz, introducing very little noise into the circuit.

Both the 5 V and 3.3 V required by the DAC are generated by ultra-low-noise positive linear regulators of the typeTPA7A4700 and TPS7A4901. Voltage dividers made by two resistors fix the output voltage, one pair for the 5 V and the other for the 3.3 V. A Schottky diode protects the input to the power supply against reverse polarity—it drops only 0.3 V from the single power supply of 7-8 V.

The 3.5-inch display goes above the Audio DAC. If necessary, use two standard-size stacking headers to place the display higher to clear the components. This will place the 25-way socket of the display above the Audio DAC PCB.

Performance

Plotting the amplitude of the output as a function of frequency shows the cut-off frequency at about 63.5 KHz. The total harmonic distortion plus noise was measured as a function of frequency with sampling rates of 48, 96, and 192 KHz shows it to be far lower than the acceptable limits—at 0.0007%. Although the RBPi generates several spurious frequencies that are just visible, the level for the fundamental frequencies is very low at -120 dB (1 µV). Those for the second and third harmonics are barely visible.

Various FFT analysis of a 16-bit, 1 KHz full-scale sine wave at different sampling rates shows the harmonic distortion to be far below the acceptable levels— at 0.002%. All these measurements show this tiny board to offer a great audio experience.