An important point regarding the cost is the option of adding an air ionizer to prevent static charges collected on pellets during the dispensing. As will be discussed in the Results and Discussion section 3, this can improve the output of the dispenser in the cases where static charges are observed, as was our case. It implies an important increase on the price (the model that we used is listed in Supplementary Information and costs around 571 euros or 600 USD), so it needs to be evaluated for the material of interest and the conditions observed. Fig. Circuit for each of the dispensers, to be repeated eight times for the full device. The Arduino UNO showed in the scheme can be substituted by an Arduino MEGA to have more available pins.