Design of a Seat Belt Interlock Circuit

The Seat Belt Starter Interlock system for 1974 Model Year automobiles was developed to comply with Motor Vehicle Safety Standard 208. A relatively complex electronics package is required to provide the seat switch and belt monitoring, decision making, and warning and starter control. To meet the logic requirements of this system, Delco Electronics chose bipolar technology to develop a custom integrated circuit. A latch is used for sequence detection and for restart memory. Input circuits are designed to avoid standby battery drain. Discrete rather than integrated power devices are used. High reliability is assured by providing protection from electrostatic discharge and other electrical transients.