Introduction

Relays are electromechanical devices that use the magnetic field of their coil(s) to open or close electrical connection(s). This can create physical isolation between two points, which has advantages over semiconductor-based solutions. However, since a relay is a moving part, it can fail in several ways, from contacts welding together to burning out the energizing coil. Safety-critical applications can use special relays, like those with force-guided contacts, to detect failures, but these components are cost-prohibitive in many cases. Applications that need a higher level of reliability, but are not in sensitive applications, may consider a simple failure detector circuit instead. In this application note, a PIC16F15245 microcontroller monitors and drives a relay while implementing Microchip’s free-to-use IEC 60730 Class B software diagnostic library.