If you’re lucky enough to visit the Netherlands and you order a hot drink, you’ll likely be given a sweet treat as well. That is a stroopwafel, a crispy little waffle-syrup sandwich that the Dutch like to rest on top of their drink so that the rising heat will soften the pastry. But Eamon Magd is just a visitor to the country and didn’t know how long to leave it, so he built this stroopwafel doneness detection device.

Magd inferred that there are three factors that, together, might help him determine when a stroopwafel becomes ready for consumption: heat, time, and movement. That last one might seem strange, but stroopwafels tend to curl up after they reach a certain point — probably a result of the sandwich style construction and a differential in temperature/moisture. So, by looking for movement, Magd thought he could detect the beginning of that process.

A computer vision application, running on Magd’s laptop, detects that movement by looking for blurry pixels. Assuming the image is otherwise sharp, blurry pixels indicate movement. Magd also used an Arduino UNO Rev3 board to detect the temperature on the surface of the stroopwafel with a simple temperature sensor. The Arduino displays the current time since start on a small LCD and sounds an alarm through a buzzer when it determines that the stroopwafel has softened to Magd’s liking.

The system attempts to guess the right moment using a linear regression model trained on input data Magd collected. He tried to account for beverage types, as some might soften the stroopwaffel faster than others, but the model is really just working on averages anyway. It doesn’t, for instance, differentiate between stroopwafel makers. Regardless, this is an amusing project.