Alarm Clock

Contents

• Overview
• Hardware
• Firmware
  • Interrupts
  • Flags
  • Compile & Flash
• Demonstration
• Credit

Overview

I built a prototype circuit for a simple alarm clock. This was designed such that the user starts by setting the time and alarm with pushbuttons. The time would then start to increment as on an everyday clock. When enabled, a speaker circuit would sound the alarm (until it's disabled or 1 min has elapsed).

Once the clock is configured, the alarm and time display mode could be adjusted with the original pushbuttons.

Hardware

This was built with the following electronic kit equipment:

• N76E003 microcontroller to power and control the circuit.
• CEM-1203 magnetic buzzer transducter, FQU13N06LS MOSFET and 1N4148 diode for the speaker.
• CM-S01602DTR/M LCD for the time/alarm display.
• Pushbuttons to change the program settings.

Firmware

This was implemented in 8051 ASM for the N76E003 microcontroller. The program consisted of a main loop to receive user input (i.e. via pushbuttons) and update the LCD display. Interrupt Service Routines (ISR) were used to implement the underlying timer and alarm functionality.

Interrupts

Timer2_ISR updated the time and checked if the alarm should be enabled. It asynchronously wrote to the BCD_Time_ and BCD_Alarm_ 1 byte defined spaces to share data with the Update_LCD_Display function in the main program.

Timer0_ISR generated the square wave for the speaker.

Note that LCD functionality was required to be synchronous due to the high latency and lower priority of operation.

Flags

Flags were used to determine program functionality across ISRs and the main program. These were designed to be similar to global variables in a higher level programming language.

These included:

• When the time was being initialized and the LCD should not be updated.
• When 1 s had elapsed and should be updated on the LCD.
• Whether the LCD display should be in AM/PM or military time mode.
• When the alarm should be enabled for generating the square wave on the output speaker.

Based on their purpose, these were either set by the main program or the Timer2_ISR.

Compile & Flash

The build tasks in the .vscode file were set up to run :

• the a51.exe executable to compile the Alarm_Clock.asm file
• the ISPN76E003.exe executable to flash the program onto the N76E003 microcontroller

Demonstration

I have uploaded the Demo on Youtube and have embedded a low resolution compressed version below.

Alarm_Clock.mp4

Credit

This was completed as part of the ELEC 291 - Design Studio project course in the The University of British Columbia Electrical and Computer Engineering undergraduate program. I received tremendous support and guidance from Dr. Jesus Calvino-Fraga.