Starfish Is an RP2040-Based Control Board for Pick-and-Place Machines

Many automated machine tools operate in similar ways and can share control boards. At their heart, they all follow CNC (computer numerical control) principles. This means that CNC mills, laser cutters, 3D printers, pen plotters, and many more machines contain hardware that is largely interchangeable. But some machine tools have distinct needs and can benefit from dedicated controllers. 3D printers, for example, benefit from components for measuring and controlling temperature — components that are unnecessary for a pen plotter. Following that logic, Thea (Stargirl) Flowers created an RP2040-based control board called Starfish tailored to pick-and-place machines.

Flowers owns a company called Winterbloom that builds and sells synthesizers. That work requires the assembly of many PCBs, which means that she has to place a lot of small components. That is difficult and time-consuming to do by hand, which is where the pick-and-place (PnP) machine comes in. PnP machines, including the Opulo LumenPnP that Flowers owns, automatically pick electronic components (like resistors, capacitors, microcontrollers, and many more) from a reel and then place them onto the correct location on a PCB. One has to program the locations, but after doing so they can sit back while a robot assembles their PCBs for them. That saves a lot of time and effort when building many identical PCBs.

PnP machines look and operate a lot like pen plotters, because the end effector moves in two axes and experiences very little resistance. But these machines grab components using vacuum, which benefits from special hardware. They can also control the feed of the reels holding the components — though it is possible to get around that. Many PnP machines use repurposed control boards meant for other machines, like 3D printers. But that is a clumsy approach and Starfish is much more elegant.

Starfish utilizes a Raspberry Pi RP2040 microcontroller (the same as found on the Pico development board), which is powerful and affordable. It controls up to three stepper motors (one for the X axis, two for the Y axis) via Trinamic TMC2209 silent drivers. MOSFETs control power to two vacuum pumps and drivers actuate two pneumatic solenoid valves. Starfish also includes two vacuum sensors, which are very handy for ensuring reliable operation. Finally, Starfish can drive RGB LEDs, communicate with feeders via RS485, and includes I2C connections for expansion.

Flowers designed Starfish for use with a LumenPnP machine, but it should work well with many other models and DIY builds. Starfish is open source, so anyone can grab the PCB design files, have them fabricated, and then put together this control board. As a bonus, the board looks beautiful.