How to Add the Raspberry Pi Microcontroller to Your PCB
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
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.
Through-hole Mounting
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.