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Countdown Timer

Accurate timing from an AT90S1200 micro

Countdown Timer
This project is simple to build and use yet accurate enough to provide a count down from any time interval anywhere from ninety-nine minutes down to one minute. The bright two digit display shows the current minutes left, and there is a piezo buzzer to indicate when the count reaches zero!Main Features– Countdown period 1 minute to 99 minutes– 2-digit 7-segment LED display– 3-button control– Low power consumption– 3-volts battery supply– AT90S1200 microcontroller chipTo use the timer is simplicity itself. First, select the time you require, by pressing the two appropriate push buttons. For example, press the unit button once for 1×1 minute, and the tens of unit button, say, three times for 3×10 minutes. There you are: a 31-minute countdown period. As you press the two switches, the number will show on the double- digit display. Both buttons will allow you to loop continuously from nought to nine, and back to nought .
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

R1,R12,R13,R14 = 10k?
R2,R10,R11 = 470?
R3-R9 = 100? to 150? (see text)
C1 = 1µF 16V radial
C2 = 100nF
C3 = 10µF 16V radial
C4,C5 = 22pF
D1 = LED, red, 3mm dia.
IC1 = AT90S1200-12PC, order code 020296-41
LD1,LD2 = HD1131O (see text)
T1, T2 = BC327
BT1 = two 1.5V AA or AAA batteries with holder
Bz1 = 5V DC buzzer
S1 = on/off switch
S2,S3,S4 = pushbutton with 1 make contact (see text)
X1 = 4MHz quartz crystal (lowprofile model)
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