An All-Solid-State Digital Control System for Appliances

A completely solid-state control system for domestic appliances has recently been developed at the D&M Research Laboratories. While this system was developed specifically for dish-washers, it is readily applicable to all appliances that exhibit complex control problems. The heart of the system is a large-scale custom metal-oxide semiconductor integrated circuit measuring approximately 0.1 inch on a side. This digital circuit, which comprises nearly 600 circuit elements, performs all of the timing and logic functions of the control system. The logic circuit provides for seven different cycles and three distinct temperature modes. However, a greater number or complexity of cycles can readily be incorporated on the logic chip at little additional cost. The integrated circuit controls the electro-mechanical devices in the appliance (such as motors, heater, sole-noids, and lights) through a set of triacs (i.e., bidirectional thyristors). The logic chip and the triacs are mounted on a single printed-circuit board measuring less than 5 inches on a side. The board also accommodates a noninductive regulated dual-level power supply and a novel circuit for electronically contralling the motor-start windings. The all-solid-state approach to appliance control becomes increasingly attractive as new and more sophisticated features (such as motor-speed control, water-level sensing, dryness sensing, etc.) are added to appliances and as the demand for greater reliability increases throughout the appliance industry. It now appears that the solid-state control system described will be economically competitive with comparable electromechanical systems in 1 to 2 years.