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RP2350B development board Think of this as the Pico 2’s bigger sibling – more pins, more I/O, more speed, more storage and more memory. It’s perfect for breadboarding, too. Also, like the Picos, it can be purchased pre-assembled! T he Raspberry Pi Pico is well known to our readers, and has been designed into many of our projects as a drop-in, self-contained compute module. It has been a runaway success for the Raspberry Pi Foundation, with over 4 million of this handy module sold since its launch in 2021. In August 2024, they improved on it with the Pico 2, based on the new RP2350A processor, which has also been very popular. The RP2350A processor also has a lesser-known sibling called the RP2350B, which is often overlooked. This has the same features as the A variant, but comes in a larger 80-pin QFN package with 48 I/O pins vs the 30 I/O pins of the RP2350A. The Raspberry Pi foundation does not offer a module based on this chip, but recently they have made it available for individual sale – so now we can design our own RP2350B based module. Thus, we present the RP2350B Development Board. This is similar to the Raspberry Pi Pico 2, but it uses the RP2350B, with nearly all of its 48 I/O pins available for experimenters – a vast improvement over the Pico 2. This board can be used as a general-purpose compute module when you need a lot of I/O pins, or as a development board while designing a circuit around the RP2350B chip. Features The RP2350B Development Board is designed to suit solderless breadboards with two rows of 32 pins on a 2.54mm/0.1-inch pitch. This is similar to the standard Raspberry Pi Pico, and this layout can also be used as a plug-in module in your own PCB designs. In our module, 47 of the RP2350B’s 48 I/O pins are routed to the edge connectors. This is useful when you need a lot of I/O; for example, when driving a high-performance LCD panel with a parallel interface, or constructing your own multi-key keyboard. The one I/O pin not available, GPIO00, is used as the PSRAM IC chip select (CS) signal. On the edge pins of the module, we have also included numerous grounds, plus +3.3V and +5V outputs. One extra benefit of the RP2350B is that eight of the I/O pins are capable of analog measurements (vs four on the RP2350A), and these are also available for use in your programs. The diagram opposite lists the full capabilities of each I/O pin. The module is self-contained, including a 3.3V regulator. The input power supply is nominally 5V, but ∎ Processor: Raspberry Pi RP2350B ∎ Cores: two ARM Cortex-M33 and two Hazard3 RISC-V ∎ Clock Speed: default 150MHz; overclockable up to around 400MHz ∎ Flash memory: 16Mbytes ∎ RAM: 520kiB, expandable to over 8MiB ∎ I/O pins: 47 (eight with analog capability) ∎ I/O connectors: two rows of 32 pins, 2.54mm/0.1-inch pitch, 25.4mm/1-inch separation ∎ Power supply: 5V nominal (4.5-12V) <at> 95mA (150MHz clock) ∎ Size: 82 × 28mm Words by Geoff Graham | Design by Peter Mather RP2350B Assembled Board (SC7514, $30): includes a fully-assembled PCB with nearly everything from the parts list, except for the optional components a range of 4.5-12V is acceptable. A USB-C socket is provided for power and loading the firmware. The firmware loading process works exactly the same as with the Raspberry Pi Pico, ie, you hold down the BOOT switch while plugging the USB into your desktop or laptop computer. The flash memory used for storing programs and data in this design has a capacity of 16Mbytes (the Pico 2 has 4Mbytes). The PicoMite BASIC interpreter occupies just 2Mbytes, which leaves plenty of flash free to create an internal “disk drive” with a capacity of about 14Mbytes. Our design also supports an 8Mbyte PSRAM chip. This sits on the same quad SPI bus as the flash memory, and can be used to add to the internal RAM of the RP2350B. Overclocking The RP2350B Development Board is designed for overclocking, which means running the processor cores at a higher clock speed than specified in the data sheet. This enables the module to be used in high-performance applications, such as generating DVI/ HDMI video. The default speed for the RP2350B is 150MHz, but some people have claimed to have overclocked it to over 600MHz. A more reasonable goal is the 372MHz needed to generate DVI/ HDMI video. To support the faster speeds, our design uses an adjustable linear regulator to generate the digital core supply voltage (DVDD). This powers the chip’s core digital logic, and in our design, can be accurately adjusted from 1.1V to over 1.4V. Higher voltages allowing the CPU to run faster. In the Pico 2, this voltage is provided by an on-chip switching regulator, which is not suited to high siliconchip.com.au PWM PWM0B SERIAL I2C SPI COM1 RX I²C SDC SPI I2C GPIO47 SPI2 RX I²C2 SDL Pin Pin 5V 5V 3.3V 3.3V GND SERIAL PWM PWM11B GPIO01 GPIO46 SPI2 CLK I²C2 SDA PWM1A I²C2 SDA SPI CLK GPIO02 GPIO45 I²C SDL COM1 RX PWM10B PWM1B I²C2 SDC SPI TX GPIO03 GPIO44 SPI2 RX I²C SDA COM1 TX PWM10A GND GND GPIO04 GPIO43 SPI2 TX I²C2 SDL GPIO05 GPIO42 SPI2 CLK I²C2 SDA I²C SDL COM2 RX PWM8B SPI2 RX I²C SDA COM2 TX PWM8A PWM2A COM2 TX I²C SDA PWM2B COM2 RX I²C SDC SPI RX PWM3A I²C2 SDA SPI CLK GPIO06 GPIO41 PWM3B I²C2 SDC SPI TX GPIO07 GPIO40 GND GND GPIO08 GPIO39 SPI TX I²C2 SDL GPIO09 GPIO38 SPI CLK I²C2 SDA PWM4A COM2 TX I²C SDA PWM4B COM2 RX I²C SCL SPI2 RX PWM5A I²C2 SDA SPI2 CLK GPIO10 GPIO37 PWM5B I²C2 SCL SPI2 TX GPIO11 GPIO36 GND GND PWM6A COM1 TX I²C SDA SPI2 RX GPIO12 PWM6B COM1 RX I²C SCL GPIO13 PWM10B COM2 TX PWM10A GPIO35 SPI TX I²C2 SDL GPIO34 SPI CLK I²C2 SDA PWM7B I²C2 SCL GPIO15 GPIO32 GND GND GPIO16 GPIO17 COM1 RX I²C SCL SPI RX PWM9A COM1 RX PWM8B SPI RX I²C SDA COM1 TX PWM8A GPIO31 SPI2 TX I²C2 SDL PWM7B GPIO30 SPI2 CLK I²C2 SDA PWM7A I²C2 SDA SPI CLK GPIO18 GPIO29 PWM1B I²C2 SCL GPIO19 GPIO28 GND GND GPIO20 SPI RX PWM9B I²C SDL PWM1A SPI TX PWM11A I²C SDA GPIO33 COM1 TX I²C SDA PWM11B SPI RX GPIO14 PWM0B PWM9A COM2 RX I²C2 SDA SPI2 CLK PWM0A PWM9B I²C SDL PWM7A SPI2 TX PWM11A I²C SDL COM1 RX PWM6B SPI2 RX I²C SDA COM1 TX PWM6A GPIO27 SPI2 TX I²C2 SDL PWM2A COM2 TX I²C SDA PWM2B COM2 RX I²C SCL GPIO21 GPIO26 SPI2 CLK I²C2 SDA PWM3A I²C2 SDA GPIO22 GPIO25 I²C SDL COM2 RX PWM4B PWM3A I²C2 SCL GPIO23 GPIO24 I²C SDA COM2 TX PWM4A 3.3V 3.3V SPI TX clock speeds because of the electrical noise it generates. Additionally, it is difficult to implement, as it requires a specialised inductor, which is hard to find. In our design, the DVDD voltage is provided by a TPS7A7002DDAR linear regulator (REG34) that is both inexpensive and does not generate any electrical noise. The onboard trimming resistor (VR1) is used to set the DVDD voltage. Note that it is important that this is set before power is applied to the board. If DVDD is accidentally set too high, it can damage the RP2350B chip. We have also used an integrated crystal oscillator to generate the base clock of 12MHz for the RP2350B. This is different from Raspberry Pi Pico 2, which uses a simple crystal for this purpose. The integrated crystal oscillator provides a more stable clock with much less jitter. Jitter can be a problem siliconchip.com.au when the base clock frequency is multiplied many times in the RP2350B to give the core CPU clock. Development environments All the familiar development environments used with the Raspberry Pi Pico 2 can be used with this board. This includes: ∎ The official Raspberry Pi C SDK for C/C++ development, which can be used from the command line on a desktop or laptop computer, or within popular integrated development environments like Visual Studio Code (VS Code), Eclipse and Clion. ∎ MicroPython, which is a full implementation of the Python 3 programming language running directly on the Development Board. This includes an interactive prompt to execute commands immediately via a USB serial port. ∎ Our own PicoMite firmware, Australia's electronics magazine SPI2 RX PWM5B PWM5A ANALOG PIN which implements a feature-rich BASIC interpreter (MMBasic) with support for audio, LCD panels, SD cards, game controllers, HDMI/VGA video and PS2/USB keyboards. This firmware includes its own full-screen editor so programs can be developed, tested and run on the development board in a highly productive environment. Circuit details Fig.1 shows the full circuit for the RP2350B Development Module. At the centre is the RP2350B processor. All its general-­purpose I/O pins are routed to the two connectors at the edges of the The RP2350B has the same features as the RP2350A in the Pico 2 but has more pins, including 48 GPIOs. August 2025  47 Fig.1: the circuit diagram for the RP2350B Development Board/Module. USB-C socket CON2 is used both for supplying power (5V DC) and communicating with the RP2350B. The USB 5V supply is regulated to 3.3V by REG21 to power oscillator XO4, PSRAM IC33 and flash chip IC6. The RP2350B's nominally 1.1V core supply is generated by adjustable regulator REG34, so it can be increased for overclocking. 48 Silicon Chip Australia's electronics magazine siliconchip.com.au PCB (CON35/36), except for GPIO00, which is used as the chip select signal for the PSRAM (IC33). One other pin (GPIO25) is special as it drives the onboard LED, LED2. If you do not need this indicating function, the I/O pin can be used as a general purpose I/O with the extra load presented by the LED and its 1kW current-­ limiting resistor. The input power for the board is a nominal 5V DC; the RP2350B and the other chips on the board run from 3.3V, which is supplied by a simple AMS1117-3.3 low-dropout linear regulator. The official Raspberry Pi Pico modules have a much more complex design for the power supply, using a switching regulator, but this can cause significant electrical noise that interferes with analog measurements and sensitive circuits such as audio input/ output. Most designs do not need the wide voltage range of the switching regulator, so our design avoids the noise problems and still provides a useful input supply voltage range of 4.5-12V. The RP2350B needs another voltage supply called the digital core supply (DVDD), which we mentioned earlier as essential for overclocking. This powers the chip’s core digital logic. In our design, it is provided by REG34, an adjustable linear regulator controlled by trimpot VR1. IC6 is a W25Q128JVSIQ 128Mbit (16Mbyte) flash memory chip made by Winbond Electronics. It uses a quad SPI interface and is designed for true XIP (execute in place) operation, which allows the RP2350B to execute its program directly from this chip. The W25Q128JVSIQ can operate with high clock speeds on the SPI interface (133MHz); this is important when overclocking the RP2350B. The RP2350B also has a built-in SRAM cache, which operates to mitigate the effect of the relatively slow quad SPI bus interface. The BOOT pushbutton switch (S16) pulls the chip select line (CS) low on the flash memory chip, which essentially disables the flash memory. When power is applied, the RP2350B will interpret the disabled memory as a signal to enter its bootloader mode, which is used to load a new firmware image. IC33 is an optional external PSRAM chip (APS6404L-3SQR-SN), which sits on the same quad SPI bus as the siliconchip.com.au Parts List – RP2350B Development Board 1 double-sided PCB coded 07107251, 82 × 28mm 2 momentary SMD tactile pushbutton switches (S15, S16) [XKB Connectivity TS-1187A-B-A-B] 1 USB-C USB 2.0 data + power socket (CON2) [Kinghelm KH-TYPE-C-16P] 1 50kW 3.8 × 3.6mm SMD trimpot (VR1) [Bourns TC33X-2-503E] 2 32-pin male headers, 2.54mm pitch (optional) Semiconductors 1 128Mbit QSPI flash memory, SOIC-8 (IC6) [Winbond W25Q128JVSIQ] 1 Raspberry Pi RP2350B microcontroller, QFN-80 (IC28) 1 APS6404L-3SQR-SN 8MiB PSRAM, SOIC-8 (IC33; optional) 1 12MHz oscillator module, 3.2 × 2mm SMD-4 (XO4) [TOGNJING XOS32012000LT00351005] 1 AMS1117-3.3 low-dropout 3.3V linear regulator, SOT-223-3 (REG21) 1 TPS7A7002DDAR adjustable low-dropout voltage regulator, SOIC-8 (REG34) 1 white SMD LED, M1608/0603 size [KT-0603W] Capacitors (all SMD multilayer ceramic capacitors) 3 10μF 50V X5R, M3216/1206 package [Samsung CL31A106KBHNNNE] 18 100nF 16V X7R, M1206/0402 package [Samsung CL05B104KO5NNNC] 1 10μF 10V X5R, M1608/0603 package [Samsung CL10A106KP8NNNC] Resistors (all SMD M1206/0402 ±1% unless noted) 1 1MW 2 1kW 2 20kW 1 33W 5 10kW 2 33W (0603 size) 2 5.1kW 2 150W (0603 size) The finished RP2350B Development Board shown at 75% of actual size. The 32-pin headers are not included with the assembled board flash memory chip. This has a capacity of 64Mbits (8Mbytes) and it can be used to augment the internal RAM of the RP2350B. How it is actually used depends on the running program. For example, PicoMite BASIC will automatically add it to the general-­ purpose RAM seen by the BASIC interpreter, allowing for very large arrays to be defined. Because the PSRAM must communicate over a serial interface, it is a lot slower than the internal RAM of the RP2350B. It also can limit the amount of overclocking that the board is capable of; however, it should still reach the speeds needed for generating DVI/ HDMI video. The internal RAM is normally more than enough for most applications, so for this and performance reasons, the PSRAM location is not populated in our design. However, it can be easily added to the BOM (Bill of Materials) for automated assembly or, as it is in an easy-to-solder 8-pin SOIC package, you can add it yourself. Australia's electronics magazine This chip is available from Mouser for around $3 in small quantities: https://au.mouser.com/ProductDetail/­ 878-APS6404L-3SQR-SN Building it The RP2350B chip comes in an 80-pin QFP package, which is designed for automated surface-mount soldering. It can be hand soldered, but this is a challenge, even for someone skilled in SMD soldering. So, practically speaking, you have two options for obtaining this module. You can purchase it fully assembled from the Silicon Chip Online Shop, or you can use an SMD assembly service such as JLCPCB’s to build the board. We recommend JLCPCB (https:// jlcpcb.com) for the automated assembly, as they have proved reliable and reasonably priced in the past. JLCPCB also source the components at a good price and they do everything, including making the board, making the solder stencil, applying the solder paste, August 2025  49 Resistance (TP1-DVDD) DVDD 6.0kΩ 1.10V 9.0kΩ 1.15V 12.0kΩ 1.20V 15.0kΩ 1.25V 18.0kΩ 1.30V 21.0kΩ 1.35V 24.0kΩ 1.40V 27.0kΩ 1.45V 30.0kΩ 1.50V 33.0kΩ 1.55V 36.0kΩ 1.60V Fig.2 (above): the overlay diagram for the RP2350B Development Board. The table at the top of the page can be used as a reference for overclocking the RP2350B IC. placing the components and reflow soldering them. Their minimum quantity for assembly is two boards. However, if you do want a number of boards, it is hard to see why you would want to undertake the hand assembly of this board when the automated assembly option is relatively cheap. To order boards from JLCPCB, you will need to download three files from siliconchip.au/Shop/10/2832 (they all come in one download package). The package includes a ZIP file with the Gerber files that contain the PCB design, a Bill of Materials spreadsheet listing all the parts required, and a CPL spreadsheet that contains the placement information for the pickand-place robots. Ordering assembled boards from the JLCPCB website is reasonably simple. Go to https://jlcpcb.com and create an account with them. Then, drag and drop the “RP2350B Development Board Gerbers.zip” file onto the “Add gerber file” box to the left of the Instant Quote button on their front page. The website will process the file and display an image of the PCB. Click on the switch marked “PCB Assembly”, then click “NEXT” until you reach a screen that prompts you to drag and drop the “RP2350B Development Board BOM.xlsx” and “RP2350B Development Board CPL.xlsx” files. After supplying those files, you can continue and then accept all the defaults. However, you may wish to change the quantity of PCBs made (minimum of 5), and the number that you want assembled (minimum of 2). Note that boards purchased from the Silicon Chip shop or assembled by JLCPCB will not include the two 32-pin headers required for use with a solderless breadboard. You will have to add these yourself (if required). Adjusting the DVDD voltage When you receive the boards, there is one adjustment that you need to make: using VR1 to set the digital core supply voltage (DVDD). The RP2350B Development Board has all its components mounted on the top, with the pin designations listed on the reverse. It is available fully-assembled, apart from the two pin header strips. The module is quite small at 82×28mm (shown here enlarged for clarity). It is designed to suit solderless breadboards, with two rows of 32 pins on a 2.54mm/0.1in pitch, or it can be used as a plug-in module in your own PCB designs. 50 Australia's electronics magazine Important: the potentiometer must be adjusted before applying power to the board. Leaving it in a random position may damage the RP2350B chip. Set your multimeter to the resistance mode and, with the board unpowered, place the leads across the test points marked DVDD and TP1. Adjust potentiometer VR1 to give a reading of 6kW. This will set DVDD to 1.1V, which is the standard voltage for a clock speed of 150MHz (the default for the RP2350B). This should also work for clock speeds up to 250MHz. If you wish to overclock the RP2350B, you need to do two things: increase DVDD and set the desired clock speed in the program by setting CPU registers. Typically, a DVDD of 1.3V will allow the RP2350B to run up to 400MHz, with intermediate values suitable for clock speeds between 250MHz and 500MHz. The table at left lists some resistance values and the resultant DVDD voltages. A maximum of 1.4V for DVDD should be safe. However, if you wish, you can try higher voltages with a risk of damaging the RP2350B processor. When the board is powered, this setting can be checked by measuring the voltage between the DVDD test point and any GND point. Note that overclocking the RP2350B Development Board is not guaranteed, although all the samples we tested have reached a speed close to 400MHz. Also note that when a PSRAM chip is fitted, the maximum overclock speed will typically be slightly reduced. Using the module Power for the board is supplied via the USB-C connector. This is the normal mode when you are developing a program, as the board will be connected to a desktop or laptop computer that is used to load or edit the program. When the board is used as an embedded controller (ie, not connected to a computer), power can be supplied via a 5V pin on the edge connector. This supply can be 4.5-12V. In this case, you cannot use the USB connector at the same time, as that would cause a conflict between the two power supplies and possibly damage your computer. To prevent this possibility, you can use a switch or jumper to isolate your power supply whenever the USB connector is used. siliconchip.com.au ◀ The RP2350B Development Board is ideal when you need many I/O pins. One example is driving a high quality LCD panel with a parallel interface; this can require 15-23 I/Os, difficult for a Pico 2 to accommodate but easy with our module. Some development environments, such as MicroPython and the PicoMite BASIC interpreter, use the USB connector with a terminal emulator on a computer to edit and manage the programming environment. Other, hosted development environments, such as the C/C++ compiler, will build the program on the desktop or laptop computer, which then needs to be transferred to the module. To load this firmware, you simply hold down the BOOT button while restarting the module (the RESET button is good for that) and then copy the firmware to the pseudo USB drive that is created on your computer by the RP2350B chip. How you use the RP2350B Development Board will depend on the firmware that you have running on it. The PicoMite BASIC interpreter can be downloaded from siliconchip.au/ Shop/6/833 This is a complete OS with a Microsoft BASIC compatible interpreter and extensive hardware support, including HDMI/VGA video, PS/2 and USB keyboards, touch-sensitive LCD panels, SD cards and much more. For a full description of the PicoMite firmware, read the article on the Pico­ Mite 2 (February 2025; siliconchip.au/Article/17729) or visit the author’s website at https:// SC geoffg.net Songbird An easy-to-build project that is perfect as a gift. SC6633 ($30 plus postage): Songbird Kit Choose from one of four colours for the PCB (purple, green, yellow or red). The kit includes nearly all parts, plus the piezo buzzer, 3D-printed piezo mount and switched battery box (base/stand not included). See the May 2023 issue for details: siliconchip.au/Article/15785 siliconchip.com.au Australia's electronics magazine August 2025  51