Building over algorithms previously developed for digital pens, this article introduces a novel 2D localization technique for mobile robots, based on simple printed patterns. This method combines high absolute accuracy (below 0.3mm), unlimited scalability, low computational requirements (the presented open-source implementation runs at above 45Hz on a low-cost microcontroller) and low cost (below 30 Euros per device at prototype stage). The article first presents the underlying algorithms and localization pipeline. It then describes our reference hardware and software implementations, and finally evaluates the performance of this technique for mobile robots.