Electronic Component Selection
Below are the components that were selected for the display and control boards.
Display Board Parts
LED displays – All LEDs are made by Kingbright. These were selected because of the availability of alphanumeric displays.
3mm LEDs – These are used for the colon’s and AM/PM indicators. All Kingbringt T-1/3mm through hole, red WP132XID, green WP132XGD, yellow WP132XYD. These LEDs are much brighter than the Alpha/Numeric displays. 470 ohm resistors are used in series with the red and green and 220 ohm resistors are used with the yellow to match brightness. These values are not on the schematic and were found though experimentation.
LED Driver – HT16K33, 28 Pin SOP-A. All versions of this chip have the same model number, output capability is determined by pin count. While breakout/backpack boards using this chip are common, the chip is not stocked by major distributors. Buying breakout/backpack boards and de-soldering the chips was the quickest way to get them.
I2C Connectors – Molex 47053-1000 headers, 1 per display board,
Other parts – All other resistors are 1/8w 1% or 5% 0805 thick film SMD. Diode for HD16K33 are MCC 1N4148WX-TP SMD SOD-323. AVX 08053C104KAT4A 0805 SMD bypass capacitor. Nichicon UWX1A220MCL1GB bypass SMD capacitor. See schematic for values.
Control Board Parts
Arduino Nano Based v1.0 Controller – This one uses a standard Arduino Nano v3.2. Two Gravitech 15Fx1-254mm 15 pin female headers for it to plug in to the board.
ATmega328p-au Based v2.0 Controller – ATMEGA328P-AU-ND 32-TQFP, 16MHz surfacne mount TXC 9C-16.000MEEJ-T crystal, 2 22pF Vishay VJ0805A220GXAPW1BC 0805 surface mount capacitors. Liteon LTST-C170GKT 0805 SMD green LED for power indication and a Liteon LTST-C170YKT 0805 SMD yellow LED for status indication.
Real Time Clock – Maxim DS3231S SMD SOIC-16. Chose for it’s high accuracy temperature compensated crystal and battery backup.
I2C Connectors – 3 Molex 47053-1000 headers,
Battery Holder – Renata SMTU1632-LF SMD for 1632 battery.
DC Power Jack – Kobiconn 163-179PH-EX 2.1mm inside, 5.5mm outside.
Buttons – 3 C&K PTS645VK832LFS tactile switch, through hole.
Protection – Littlefuse 0470002.DRSNP 2A SMD fuse. Littlefuse SMBJ5.0A for transient and reverse voltage protection.
Power Supply – Mean Well SGA12U05-P1J 5v 2.4A power supply wtih 2.1mm barrel plug. Clock actually draws about 1.1A. Alternate longer cord (1.8M) version Mean Well GS15U-1P1J.
Other Parts – All other resistors are 1/8w 1% or 5% 0805 thick film SMD. AVX 08053C104KAT4A 0805 SMD bypass capacitors. Nichicon UWX1A220MCL1GB bypass SMD capacitor. See schematic for values.
I2C Cables – For connection between control and display boards. Red, Black, Blue White 22awg stranded. 6 Molex 47054-1000 housings, 24 Molex 08-55-0102 socket pins. Crimp with Molex #63811-1000 tool. Crimp bare wire at 1.6mm, insulated at 1.8mm.