LED Clock

Overview

[Insert pithy overview of LED clock project. Or just refer to the links.]

Chronology

[Insert pithy introduction to the list of blog entries about the clock.]

Inspiration
The Font
Ordering Parts
LED Control Bus Architecture
Testing the A6276 LED Driver
Programming the A6276 LED Driver
Enough Controller Pins?
LED Numbering Order
Numbering Order Animated!
Numbering Order Reanimated
Daylight Savings Time
498 LEDs
Board Layout
Prototype PC Board
Prototype Digit Assembly
It’s Blue. It’s Beautiful.
Disputing Resistors
Resistor Dispute Continues
Interfacing to the DS1302 RTC Chip
Escalating Resistor Dispute
Working DS1302 RTC Interface!
DS1302 Unworking
Troubleshooting the DS1302
It’s the Voltage, Man (DS1302)
$6 Refund for Wrong Resistors
DS1302 + A6276 = Visible Demo
Laying Out the Full Display
Serial Communication, MAX232, and Programming the LogoChip UART

Materials and Costs

Item Qty Purchased Cost Qty / Clock Cost / Clock
blue LEDs 500 $50.35
$1.00 insurance
free shipping

$51.35 total
∼180 $18.49
PIC18F2320 microcontroller 2 free samples 1
Allegro A6276 16-channel constant-current LED drivers 4 free samples 12

Resources for Remaining Materials

Allegro Microsystems A6276 LED Driver

  • 2 clocks ⋅ 12 drivers / clock = 24 drivers
  • have 4 samples; need to buy 20
  • Allegro Microsystems home page for stock check search
  • Arrow: 1 @ $1.80 (no quantity discount)
  • Newark: 1-24 @ $2.28; 25-49 @ $2.17
  • Digi-Key: DIP is non-stock item; minimum 525 @ $1.32

Power Supply

  • need 2 (one per clock)
  • (∼.6A / digit) ⋅ 6 digits ≈ 3.6A @ 5V minimum, plus a little for controller
  • All Electronics choice #1:
    • $7.50
    • 6.78″ x 3.65″ x 1.72″
    • 12Vdc @ 2.0A, 5Vdc @ 8.0A, -12Vdc @ 2.0A.
    • Eh.
  • All Electronics choice #2:
    • 1-13 @ $6.50; 14+ @ $5.50
    • 5″ x 3″ x 1.28″
    • 5 Vdc @ 8 amp. 3.3 vdc @ 4 amp. 2.5 vdc @ 2 amp.
    • Love the size! Like that it has low ratings for voltages I don’t need.
  • All Electronics choice #3:
    • 1-9 @ $3.50; 10-99 @ $3.00
    • 8″ x 3.5″ x 1.25″
    • 5 Vdc 7 A, 3.3 Vdc 15 A.
    • Love the price! Don’t need 15A of 3.3V (and the circuitry to support it), though.
  • Enclosure

Don’t Forget

Remember to put connections on the main board for LogoChip cloning and/or in-circuit programming.