6.6 PRACTICAL APPLICATION: A CASE STUDY 325
a rate of about 10,800 bps. Microprocessor-controlled modems are known assmartmodems, such
as the Hayes modem, manufactured by Hayes Microcomputer Products. The portableacoustic-
couplerdevice, which is a different type of voice-band modem, is a low-speed modem with a
rate of about 600 bps that is connected acoustically to a standard telephone. Wide-band modems
are very high-speed modems with rates of 19,200 bps and above, designed for use with dedicated
telephone lines. These are currently used mostly on private communications systems.
6.5 Learning Objectives
Thelearning objectivesof this chapter are summarized here, so that the student can check whether
he or she has accomplished each of the following.
- Understanding continuous, discrete, and binary digital signals.
- Performing operations with binary, octal, hexadecimal, and binary-coded-decimal number
systems.
- Logic symbols and truth tables for various gates.
- Designing simple combinational logic circuits using logic gates.
- Using Karnaugh maps to realize logic expressions.
- Sketching timing diagrams for sequential circuits based on flip-flops.
- Digital system components such as decoders, encoders, multiplexers, registers, counters,
D/A and A/D converters, memory, and display devices.
- Basic understanding of computer systems.
- Basic notions about computer networks.
6.6 PRACTICAL APPLICATION: A CASE STUDY
Microcomputer-Controlled Breadmaking Machine
Figure 6.6.1 shows a simplified schematic diagram of a microcomputer-controlled breadmaking
machine. A microcomputer along with its timing circuit, keypad, and display unit controls the
heating resistor, fan motor, and bread-ingredient mixing motor by means of digitally activated
switches. An analog temperature sensor, through an A/D converter, provides the status of
temperature to the microcomputer. A digital timer circuit counts down, showing the time remaining
in the process.
The control programs are stored in ROM and determine when and how long the machine
should mix the ingredients added to the bread pan, when and how long the heating resistor should
be turned on or off for various parts of the cycle, and when and how long the fan should be on to
cool the loaf after baking is finished. The parameters such as light, medium, or dark bread crust
are entered through the keypad into RAM.
According to the programs stored and the parameters entered, the machine initially mixes
the ingredients for several minutes. The heating resistor is turned on to warm the yeast, causing
the dough to rise while a temperature of about 90°F is maintained. The time remaining and the
temperature are continually checked until the baked loaf is cooled, and the finished bread is finally
ready in about 4 hours.
Microprocessors and computers in various forms are used extensively in household appli-
ances, automobiles, and industrial equipment.
