MC68HC705KJ1 Features
16-Pin Plastic DIP, Ceramic DIP, and SOIC Packages
4 MHz Maximum Operating Frequency at 5 Volts
Multifunction Timer with 15-Stage Ripple Counter
Computer Operating Properly (COP) Watchdog Timer
10 Bidirectional I/O Pins
- Software Programmable Pulldown Devices on All I/O Pins
- 10 mA Current Sink Capability on All I/O Pins
- Optional Active High Interrupt Capability on 4 I/O Pins
Selectable Sensitivity on External Interrupt Request Line
On-Chip Oscillator for Crystal, Ceramic Resonator, or Resistor-Capacitor Network
Internal Steering Diode and Pullup Device from RESET Pin to VDD
Notes:
For it to be an affordable replacement for conventional dimmers, the smart light dimmer needs a cost-efficient microcontroller. The MC68HC705KJ1 fits the bill by providing features appropriate for this application.
Apart from the EPROM and RAM used for program and variable storage, the smart light dimmer depends on three MC68HC705KJ1 features. In the schematic diagram that follows, a triac controls the AC waveform seen by the light bulb. Because it has 10 mA current sink capability on all of its I/O pins, the MC68HC705KJ1 can drive this triac directly. A less capable device would require triac drive hardware that would increase the smart light dimmer’s cost.
The triac automatically turns off each time the AC waveform crosses zero. By using both the active low IRQ interrupt and the optional active high interrupt capability of the low order port A pins, an interrupt is generated each time the AC waveform crosses zero.
With the multifunction timer, a delay can be inserted between each zero crossing and subsequent firing of the triac. This delay determines the conduction period of the triac, the length of which is directly proportional to the brightness of the light bulb.