An Arduino-Controlled Photogate

It is hard to imagine teaching physics without doing experimental measurements of position as a function of time. These measurements, needed for the determination of velocity and acceleration, are most easily performed with the help of photogates.^1,2 Unfortunately, commercial photogates are rather expensive. Many require the purchase of an additional matching timer or other electronic device. Sometimes special software is also needed. The total bill can easily become prohibitive. For this reason physics teachers have shown considerable interest for cheaper, in-house designed and manufactured photogates.^3–6 The photogate systems described in the literature have their limitations. Some rely on a digital stopwatch and therefore cannot measure time with a precision higher than 0.01 seconds. Some use photoresistors that have a slower response than phototransistors. Some are based on the computer microphone port and therefore cannot handle more than two photogates (two audio channels) at the same time. Extracting the time information from an audio file can also be a challenge for some students. We describe here a photogate system that matches the performance of a commercial one but at a fraction of the cost. The key to this success is the use of an Arduino microcontroller for data collection. The Arduino platform, initially developed for electronics and robotics educational projects, has recently been incorporated in physics labs.⁷ The Arduino microcontroller, because of its low cost and because it provides a broad exposure to electronics and computer programming, is an ideal tool for integrated STEM projects.