High-end dishwashers have drying systems by means of TEC condensers or gates for ventilation, but most don't.
Opening the door after the program finishes helps getting all the moisture out and avoids condensation and water marks on the dishes, sometimes even bad smells if you leave it overnight.
An actuator behind the scenes is commanded by a microcontroller that uses a microphone to listen for the "beep" sequence at the end of the program, then opens the door for you.
The actuator is installed in the adjacent cabinet and everything is hidden by the door. The actuator pushes the cabinet door and the dishwasher door at the same time, then hides out of sight.
During the last minute I resoldered the microphone so it aligns perfectly with the whole on the enclosure so I would not have to raise the gain. It is quite sensitive but the software waits for 3 beeps spaced 6 seconds apart. It seems quite reliable.
So far I have only tested by generating the tones with Audacity. Here is a short video of the detector reacting to the dishwasher beeps (not the end of cycle long beeps, but it's the same frequency.)
A cheap microphone capsule salvaged from the junk bin, together the old and ugly LM358 as preamp, feed the audio signal to the STM32F103 (bluepill, bottom dev kit). For this MCU, at 72 MHz, with a DMA capable 12-bit ADC, sampling the audio is a walk in the park. I plan to use the ESP (top) to do the IoT / wifi part of this project.
Ideally you'd use just one MCU, but the ESP has a very slow ADC that is not intended for audio, and though I have a couple SPI codecs (the unconnected Microchip part on the upper breadboard), it was much simpler to do the heavy ADC+processing job on the ARM Cortex chip.
Parts wise... the bluepill is even cheaper than the SPI ADC part!
I designed two clamps and a "finger" (that hopefully won't snap!) It's just 3mm thick. If it breaks I will have to redo the end with something stronger
Most of the mechanic part of this hack will be built around a suitable actuator than can push my dishwasher door open. I ordered one of these, with a 200mm travel and rated at 700N it should be more than capable of opening the door. Speed is not really important.
Thanks for your input! By lock I think you mean the type of latch that would be actuated by the door handle; thankfully my dishwasher, a basic BOSCH, only needs you to pull the door with a certain force and it will just snap open. I think this is the case for most built-in/integrated dishwashers. I ended up ordering a slow and cheap linear actuator, china-rated at 700N. Hopefully will do!
We also have a Bosch in the US. It does not have a separate lock mechanism. Ours does not beep when done, the display shows 00 for the time and that is the end of it
We have both types around, but for new kitchens this side of the Atlantic, the so called "integrated" models are often used. The dishwasher comes with no latch because you have to attach an MDF/wood panel to the front of it so it looks the same as the rest of your kitchen furniture. The handle is then a regular cupboard/cabinet handle. The latch is replaced with a catching mechanism that makes closing lighter than opening (not the best for my purpose, BTW)
Smooth operation, nice job getting this one across the finish line!