Computer-Driven Power Controller

This circuit enables a computer to con- trol the power supplied to a mains oper- ated device (lamp, heater, drill, etc.) in 255 steps. Variation of power is achieved by controlling the voltage supplied to the load (RL in the circuit diagram of Fig. 2). A conventional power regulator is used here, composed of a triac and a simple associated circuit to control the phase angle at which the triac is trig- gered. The power supply and mains trigger cir- cuitry are shown in Fig. 1. The circuit around Ti . .T4 incl. and ICI is a zero- crossing detector which produces an active high pulse every time the mains voltage is zero. Opto-coupler ICI in- sulates the rest of the circuit from the mains. With reference to Fig. 2, Schmitt-trigger Ni inverts the zero-crossing pulses, causing 8-bit binary down counter ICa to load the 8-bit word applied to counter preset (jam) inputs Ja . J7. The counter is decremented one count by each clock pulse supplied by oscillator N2. When counter state nought is ...