Multi-event Alarm Clock

In control of many daily events

Published in issue 1/2004 on page 0

A regular alarm clock, whether stuffed with electronics or of the mechanical variety, will not get you very far if you need to be reminded of several events during the day (for example, taking your medication). What you need is a multi-talent like the circuit described here. The circuit diagram of the Multi-event Alarm Clock shown in Figure 1 is easy to understand, the central parts being a contemporary combination of a microcontroller, a real-time clock and an LC display. At the heart of the circuit sits a powerful yet inexpensive and widely available 8051-compatible 8-bit microcontroller type AT89C2051 from Atmel. Its main features may be summarized as follows:– full 8051 software compatibility;– 2 kbytes of Flash memory;– integrated analogue comparator;– multiple outputs with LED drive capability;– static architecture (0-24 MHz)– extended supply voltage range (2.7-6 V).

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Products

Components

Resistors:
R1 = 1kOhm
R2,R3 = 47kOhm
R4 = 10Ohm
R5,R6,R7 = 4kOhm 7
R8 = 1Ohm 5
R9 = 100Ohm
R10 = 220Ohm
P1 = 10kOhm preset
P2 = 2kOhm 5 preset
Capacitors:
C1,C2 = 33pF
C3 = 1µF/63V radial
C4,C6,C7,C10 = 100nF
C5 = 25pF (trimmer)
C8 = 220µ F 10V radial
C9= 10µ F 63V radial
C11 = 470µ F 16V radial
Semiconductors:
D1 = LED, red, 5mm, low current (optionally with chassis-mount holder)
D2 = 1N4001
T1 = BC547B
T2 = BD242
T3 = BC557C
T4 = BF256C
IC1 = AT89C2051-12PC, programmed, order code 020304-41
IC2 = DS1307
IC3 = 4805
Miscellaneous:
JP1 = 3-way pinheader with jumper
S1,S2 = pushbutton, 1 make contact, chassis mount
LCD1 = LC display, 16 characters (2 lines x 8), e.g. AV0820 from Anag Vision) plus 16-way boxheader
X1 = 6MHz quartz crystal (parallel resonance)
X2 = 32.768 kHz quartz crystal
BT1 = 3V Lithium cell type CR2032 with PCB mount holder (22.75mm diam.)
BT2 = see text
BZ1 = 5V or 6V DC buzzer (active piezo)
PCB, available from The PCB Shop
Disk, microcontroller C (source) and hex files, order code 020304-11 or Free Download