The Insane Engineering Behind a DIY Real-Time Spray Paint Mixer

Spray paint is so good these days, but you still have to buy individual cans in the specific colors you want. If you need a lot of colors, you have to purchase, store, and carry a whole bunch of cans. Sandesh Manik wanted a kind of real-time color-mixing system for spray paint and bringing that to life required some insane engineering.

The high-level concept is simple: mix spray paint on-demand to produce any desired color. Printers already do that, as do the paint-mixing machines at hardware stores. But doing that with aerosol-based spray paint comes with unique challenges. How to you control flow from each can with precision? How do you mix color “channels” sufficiently? How do you prevent clogging? Manik had to figure out how to solve all of those problems.

Manik’s write-up is great, because it covers both his solutions and the failures he experienced along the way. One failed idea, for example, was using microfluidic channels to control flow and mix the paint. But that didn’t work because the spray paint cans have varying pressure, so Manik switched to hoses with valves to “pulse” paint in short bursts for mixing.

That, however, came with a problem of its own: off-the-shelf valves have exposed internal mechanisms that get clogged with paint. For that reason, Manik developed his own valves that work by pinching the hoses. Special toggle levers keep the cans’ nozzles down, allowing for flow whenever those valves are open. The four input tubes then join into a signal output tube, which sprays out through an atomizer nozzle at the press of a button.

The last major challenge was selecting color channel ratios and controlling the opening of the valves accordingly. An Arduino Nano handles the valve timing and Manik originally used a Bluetooth app for the user interface, but found that was difficult to use while painting. So, he switched to a simple analog control panel with potentiometers and push buttons. That’s easy to operate while wearing gloves and painting.

The completed system, called Spectrum, isn’t going to have the kind of color accuracy that we expect from professional CMYK printing. But it mixes colors very well and gives the user the ability to dial in any hue they want.