It’s somewhat ironic that just as Ubuntu readies itself for the starting wave of smart connected devices, my latest hardware hack was in fact a disconnected one. In my defense, it’s quite important for these smart devices to preserve a convenient physical interface with the user, so this one was a personal lesson on that.
The device hacked was a capsule-based coffee machine which originally had just a manual handle for on/off operation. This was both boring to use and unfortunate in terms of the outcome being somewhat unpredictable given the variations in amount of water through the capsule. While the manufacturer does offer a modern version of the same machine with an automated system, buying a new one wouldn’t be nearly as satisfying.
So the first act was to take the machine apart and see how it basically worked. To my surprise, this one model is quite difficult to take apart, but it was doable without any visible damage. Once in, the machine was “enhanced” with an external barrel connector that can command the operation of the machine:
The connector wire was soldered to the right spots, routed away from the hot components, and includes a relay that does the operation safely without bridging the internal circuit into the external world. The proper way to do that would have been with an optocoupler, but without one at hand a relay should do.
With the external connector in place, it was easy to evolve the controlling circuit without bothering with the mechanical side of it. The current version is based on an atmega328p MCU that sits inside a small box exposing a high-quality LED bargraph and a single button that selects the level, turns on the machine on long press, and cancels if pressed again before the selected level is completed:
The MCU stays on 24/7, and when unused goes back into a deep sleep mode consuming only a few microamps from an old laptop battery cell that sits within the same box.
Being a for-fun exercise, the controlling logic was written in assembly to get acquainted with the details of that MCU. The short amount of code is available if you are curious.