How to Add the Raspberry Pi Microcontroller to Your PCBBy ZM Peterson • Jan 22, 2021
I’ve always loved getting my hands on the latest and greatest microcontroller boards, which made today’s announcement of the Raspberry Pi microcontroller very special. Raspberry Pi just joined the ranks of Arduino with this week’s release of the Raspberry Pi Pico. This Raspberry Pi microcontroller board has a small footprint and a small price, but it can still compete with some of the best MCU modules on the market.
So what can the Raspberry Pi Pico offer that other microcontrollers can’t? It all comes down to the form factor and the silicon IP in the RP2040 MCU. The board also comes with the extensive development support you’d expect from the Raspberry Pi community, taking lightweight embedded design and making it broadly accessible. Let’s look a bit closer at the specs for the Pico and some applications.
Raspberry Pi Pico Microcontroller Specs
Aside from the board itself, there are the specs on the Raspberry Pi Pico microcontroller. The RP2040 is Raspberry Pi’s own Dual-core ARM Cortex-M0 MCU manufactured at the 40 nm process node. The power rating is low as one would expect with internal clocking at 133 MHz. Power regulation is applied external to the board, but there is also an on-die LDO for setting the internal core voltage and removing the need for additional regulation on the module.
What isn’t on the board is also important: there is no Wifi or Bluetooth, and there is no room for an RJ45 jack. Any of these communication methods needs to be added with a hat board or on the base board for the Pico. Otherwise, you’re stuck with GPIOs to access any peripherals. There is also no internal Flash on the RP2040; everything is done with an external 16 MB Flash chip. This lack of onboard features helps keep the price point for this board so low and makes it an excellent option for lightweight embedded applications.
The RP2040 microcontroller has the following specifications and features.
- 3V3 logic (3.0 to 3.6 V power)
- 264 KB on-chip SRAM, 16 MB external Flash
- 8 PIO state machines
- 16 PWM generators
- 30 GPIO pins w/ 4 ADCs
- 2x UART/2x SPI/2x I2C
- 2 internal PLLs for clock and USB generation
- Programming in C and MicroPython
Closeup of the Pico RP2040 microcontroller, courtesy of the Raspberry Pi Foundation.
Castellated Holes vs. Through-hole Mounting vs. Pin Headers
The design of the Raspberry Pi is unique as there is a mix of castellated holes and through-holes with standard pin header pitch. This gives three potential options for implementing the Raspberry Pi Pico microcontroller in a larger system.
SMD Mounting with Castellated Holes
One thing I like about the Pico is its castellated holes around the outer edge of the board. In addition, the back side of the board has no components, and there are only 6 exposed test points. These holes and the lack of components on the back side allow the board to be surface-mounted to a carrier board, just like you would with any other SMD component. The mounting holes can then be used to better secure the Pico to its carrier board, or the Pico can be secured directly to an enclosure with the mounting holes.
Pin Headers and Standoffs
Alternatively, you can use the pin headers with standoffs for a standalone module, just like you would with a typical Arduino module or other MCU board. Contrast this with a comparable MCU or SMD module (e.g., CC3235 or uBlox modems), which only has SMD mounting pads or castellated holes without pin headers. This gives designers more options for implementing the Pico into their designs. Using the pin headers and standoffs is a simple method for deploying a small MCU board with standard form factor you’d find in other MCU development boards.
The pin header along the back side of the castellated holes also allows through-hole mounting to a carrier board. Simply solder an unshrouded pin header onto the board and place the corresponding through-hole pattern in the carrier board. The Pico can then be placed using through-hole mounting and soldered for a secure mechanical connection. This is a much better option for harsh environments, such as in an industrial setting or in a vehicle.
Finally, I’d like to point out that the Pico board is very small compared to some other MCU boards, and it looks like it could be the size of a large USB drive. This makes it quite useful in many systems that need some lightweight processing power, but without the excessive design time required to develop a totally custom board. Personally, I might use the Pico and other SMD modules on a carrier board for prototyping from COTS components before building out something production grade. The ability to solder directly to the carrier enables functional testing that might not be possible with a standalone board like an Arduino or similar MCU dev board.
At NWES, we provide PCB design and layout services to SMBs, large enterprises, and aerospace and defense electronics companies. We’re always experimenting with the latest and greatest technology, including lightweight boards like the Raspberry Pi Pico microcontroller. We’ve partnered directly with EDA companies and multiple ITAR PCB manufacturing firms, and we help our clients get through the PCB manufacturing process with ease. Contact NWES for a consultation.