A Peek at the PicoCNC
I've been designing a new CNC controller breakout board based on the Raspberry Pi Pico. We are calling it the PicoCNC. This is a very nice little board that uses the RP2040 32 bit ARM microcontroller. The Pico's form factor is very similar to the Arduino Nano. In terms of performance, it is on a par with the STM32F4xx series and is very similar to the well known "Black Pill" boards. Though, because the Pico is made by the Raspberry Pi foundation, it is consistent - the Black Pill boards are not. The Pico is very inexpensive - $4. And there is a WiFi version, the Pico W, that costs just $6.
In designing around the Pico, I had a number of goals. Supporting 4 Axes was key. I wanted to be able to cover all the common types of CNC routers that hobbyists build. All of the standard grblHAL features needed to be available - limit switches, eStop, cycle start/feed hold (run/pause), spindle pwn and so on. It needed to be as EMI resistant as the Teensy based breakout board. And, it needed to be inexpensive enough to be an obvious candidate for replacing an 8-bit Arduino Grbl controller. I believe we have met all those goals including the last one. The all-in price including the Pico, breakout board and connectors is less than $50.
Squeezing all that onto the Pico was a challenge. The big breakthrough came when Terje Io, father of grblHAL, was able to take advantage of the programable IO (PIO) feature of the PICO to drive off chip shift registers. This allows grblHAL to support a step rate of greater than 200kHz, the max rate that most stepper driver support. By contrast, that maximum step rate that 8-bit Grbl 1.1 supports is around 30kHz. One of the exciting things about the PicoCNC is that, along with all the features of the Teensy based breakout board, it supports microSD cards. You can download GCode to the microSD card in PicoCNC and run it from there. It also has the potential for a lot of expansion - there are headers for UART, I2C and SPI. These can support a number of useful things like ModBus (to control a spindle), external control panels, ADC for plasma torch height control and others.
We are about to start shipping the PicoCNC. It is another "Unkit" - the PCB has all the surface mount components installed and only requires soldering on the connectors (and a lone trimmer resistor). The Board is priced at $28.99, the Assembly kit is priced at $14. We don't sell the Pico or Pico W but you can buy it from a wide range of distributors. (We would have to charge more than $4, there is no volume discount to the little guys like me.) For those that wish to find the connectors themselves, We have listed the all the components in the user guide. They are widely available.
About the author. Phil Barrett is a long time CNC hobbyist and designer of several breakout boards.