The electrocardiographic signal (ECG) reflects the electrical behavior of the human heart. The ECG signal is composed by different waveforms: P, Q, R, S and T. The R wave is normally the easiest waveform to identify on the ECG. The R wave is also the component with the highest amplitude and its detection allows the estimation of the heart rate. This paper is devoted to present the design of a digital filter implemented on an open hardware platform called Arduino to detect the R wave of the ECG signal. The filter design is based on the integration of a smooth filter and the first order derivative. The implemented digital filter has been tested using different ECG signals generated by a patient simulator. Finally, this paper shows a positive performance of the implemented filter in tests related to R wave detection even in the presence of unwanted noise components.