The determination of the speed of sound in air is a classical experiment, usually performed with a resonance tube apparatus. The measured value can be checked against Eq. (1), which describes the temperature dependence of the speed of sound in dry air. A modern implementation of this speed of sound investigation uses an Arduino Uno microcontroller board, an HC-SR04 ultrasonic distance sensor, and a DS18B20 temperature sensor. The distance sensor's transmitter produces a burst of eight ultrasonic rectangular pulses that travel through the air, reflect on an object placed in front at a distance d, and then return to the sensor's receiver after an echo time t. This Arduino investigation, unfortunately, is harder to perform than one might expect after a first reading of Ref. 1 or 2. In this article we discuss some sources of experimental errors that can complicate this laboratory activity, and we describe some important steps that must be included in the data collection and analysis procedure, in order to obtain successful results every time.