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3-Way Display Alarm

with 2.2-inch TFT screen

3-Way Display Alarm
3-Way Display Alarm
Labs Project
Based on a Labs project | February 2017 | Find it here
They say “Curiosity killed the cat”, as if it were some kind of undesirable character defect. But I see it more as a positive quality, essential in technical fields. Digging around, going off in search of a specific characteristic… Quite by accident, on the web I came across a little 2.2-inch diagonal TFT screen (and all its larger fellows). I felt an irresistible urge to heat up the soldering iron and take advantage of its display capabilities (text and graphics). What’s more, I still hadn’t ever used a real-time clock (RTC) device. The combination of the screen and the clock led me to this alarm-clock.

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Materials

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.

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PCB

Extra info / Update

3 different screens for displaying current date and time
Automatic display change
Alarm function with ‘snooze’ button
2.2-inch TFT screen
Real-time clock device
Programmable using Arduino IDE
Automatic screen brightness adjustment
Choice of display language

Component list

Resistors
R1 = 10kOhm, carbon film, 5%, 0.25 W, 250V
Capacitors
C1,C2 = 22pF, 50V, C0G/NP0, 0.1" pitch
C3,C4,C6 = 0.1µF, 50V, X7R, 0.2" pitch
C5 = 0.33µF, 50V, X7R
C7 = supercapacitor, EDLC, 1F, 3.6V (Panasonic type EECRG0V105H)
Semiconductors
IC1 = ATMEGA328P-PU microcontroller, 20MHz, DIP-28
IC2 = DS1302 real-time clock, DIP-8
IC3 = L78L33ACZ, 3.3V linear voltage regulator, TO-92-3
D1 = 1N4001-T
D2 = BAT85S-TR Schottky diode
PH = LDR, 20MOhm, 50mW, 100V (ref. A 906013)
X1 = 12MHz quartz crystal, CL = 18pF
X2 = 32.768 kHz crystal, cylindrical, radial lead, CL 12.5pF, 2ppm, 6.2×2mm (Raltron type R26-32.768-12.5)
Miscellaneous
BUZ1 = buzzer, 12mm
K1 = 9-way pinheader socket, 0.1" pitch
K2 = 3- way pinheader socket, 0.1" pitch
K3 = SPI board-to-board connector, 6-pin
K4 = male jack connector, centre pin 1.95mm dia., 12V, 3A (GND = centre pin!)
S1,S2,S3,S4 = tactile switch (Alps type SKHHLVA010)
28-pin DIL socket for IC1
8-pin DIL socket for IC2

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