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Company Logo TE Connectivity

  • Digital Watch using a Microcontroller

  • Created: Aug 19, 2015

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A digital watch is a device that displays time in digital form like in a set of four seven segment display with a colon in between the two seven segments or other symbols, unlike an analog watch that has rotating hands attached to mechanical gears that points to a position that has a number. Most of the digital watches are using microcontroller and LCD driver to display the time. Just like in this reference design, this circuit also uses a microcontroller and an LCD with built-in driver.

The circuitry in this reference design is made up of a microcontroller, an LCD with built-in driver, two TE 3-1825910-5 tactile switches, and some few external components. The selected supply for this circuit is 3.3V DC voltage to match the operating voltage of the LCD and its driver since the microcontroller can operate in either 3.3V or 5V DC supply voltage. The LCD in this circuit has an output of 48 rows by 84 columns. Its driver has eight pins connected to the microcontroller. The two pins (VCC and GND) are for supply voltage and ground while the LED pin is attached to one of the PWM pins of the microcontroller with a resistor in between to control the backlight brightness of the LCD using pulse width modulation technique. The four pins (SCE, SCLK, D/C and DN) are used by the microcontroller to communicate with the LCD driver. The active low SCE pin of the driver allows data from the microcontroller to be clocked in while the SCLK pin is used for clocking up to 4Mbits per second. The D/C pin decides whether a command data input or an address data input will be selected and the DN pin is used for data line. The active low RST pin is used to reset and initialize properly the LCD driver.

The circuit in this reference design uses only few components but high level programming is needed to make this circuit function well. The program is burned into the microcontroller memory and the display in the LCD screen is controlled by the two TE 3-1825910-5 tactile switches. For accurate programming of the display, refer to the datasheet of the LCD driver.



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