Subject : Microcontroller and Embedded Programming

Topic : Embedded System-The Case Studies

Difficulty : Medium

Various components of digital clock are LCD, display, switches, microcontroller, power supply, reset and clock circuit.

Interfacing is same as what we have seen in chapter 1 structure of embedded system.

1. The power supply is implemented using a transformer followed by a rectifier and finally a regulator.

2. The clock circuit is implemented using the standard circuit prescribed by INTEL for 8051. The crystal of 12MHz is used so that the 1μsec delay can be implemented easily for the timer application of 8051.

3. The delay can be accordingly adjusted to give 1μsec; after which the seconds counts. can be incremented. Once the seconds counter reaches 60, it should be reset to 0 and the minutes counter should be incremented. Also once the minutes counter reaches 60, it should be reset to zero and the hours counter should be incremented. Finally if the hours counter reaches 24, it should also be reset to zero. Thus the crystal is a very important component for timer or digital clock.

4. The standard power-on-reset circuit for the microcontroller 8051 is implemented as shown in the Fig. 12.1.a.

5. The interfacing of the 16 x 2 LCD is done. The various signals connected to the LCD display are power supply pins (i.e. Vcc and GND), the VEE pin (for intensity adjustment of LCD backlight), data pins (D0-D7). RS(To indicate a command or data to LCD), RW (To indicate read or write operation to LCD) and E (To enable pin to indicate latching of command or data).

6. The switches are connected as shown in the Fig. 12.1.a. whenever the switch is pressed a zero is obtained on the microcontroller port pin else a '1' is obtained. This can be used to identify the switch pressed. The switch may be required to do various operations on the timer like set the time, set the alarm, etc.