SolderTime Desk Clock

From Trammell Hudson's Projects

Solder:Time Desk Clock

Solder:Time Desk Clock assembly

We had three workshops on building the Spinkenzie Labs Solder:Time Desk Clock at my office and made a timelapse of the construction process.

Kit notes

Solder:Time desk clock

Soldering order

My suggested ordering of soldering:

  1. 100 Ohm resistor (brown, black, brown)
  2. Four 10K Ohm resistors (brown, black, orange)
  3. Eight 0.1uF capacitors
  4. Three diodes (be sure to check polarity)
  5. Crystal (be sure to not short pins)
  6. Five sockets (be sure to line up notch with U-shape on PCB)
  7. Voltage regulator (solder one pin to hold it in place and lay it flat against heat sink)
  8. Battery
  9. Buzzer
  10. Programming pins (12 normal headers, short side through the PCB. solder one pin then adjust for straightness)
  11. Two buttons and power jack -- done together they make a nice triangle to support the PCB
  12. Cut the Swiss pins into eight 7-pin segments and install on each of the LED modles.
  13. Install the LED modules on the side opposite the components-- be sure to note the orientation of the "bumps"
  14. Install the chips -- carefully bend the legs straight and pay attention to the U-shaped cutout on top of the chip.
  15. Smoke test it!


  • If you want to hack new hardware onto the board, do not assemble the acrylic case. It is a press fit and once assembled very difficult to get to the prototyping area.
  • Be sure to sand or file the tabs on the case; otherwise it will break the acrylic when you force it.
  • RTC not advancing or running very slow? You might have bridged the crystal legs. They are very close together.
  • Part of the display flickers, flashes or doesn't appear? Check your solder joints on the 74138 chip for that region. Each handles 1 1/3 of a display.


SolderTime Desk Clock schematic.png

  • Schematic
  • Four 5x7 red LED panels, with normal column/row address lines.
  • Three 74138 octal decoders connected to the columns (4 unused on the last decoder)
  • PORTB0-6 directly source current to drives the 7 rows inputs
  • PORTD5-7 selects the column
  • PORTC2-3 selects the decoder (01, 10 and 00. 11 = all off)
  • PIND2-3 are pulled low for the two buttons.
  • Because the currently selected decoder sinks current from all the LEDs turned on in the current column, turning on a different number of LEDs causes varying brightness.


Solder:Time Desk Clock workshop
Desk clock workshop three
  • Program as Arduino Dsomething with ATmega328P, programmer Arduino as ISP
  • When compiled with Arduino 1.0.5, there is lots of flickering.
    • Change the constant to Timer1.initialize(100) to Timer1.initialize(50) in ST2_Setup.ino
    • Or use my improved firmware.

Improved firmware

Completed clock kit and time lapse setup

My updated Arduino source files are The major changes:

  • Reworks the matrix code to use fewer magic numbers in the main loop. Hopefully easier to understand what is going on.
  • Removes (dead?) code in the startup and main loop. Perhaps left from debugging or other clock platforms.
  • Converts the font to use an ascii art bitmap for each character so that it is easier to edit. Now rather than defining characters like "127,9,25,41,70, // R", the font.c file has:
	{  // R
  • Converts from a 1-bit monochrome to 8-bit grayscale and adds per-pixel PWM support. Pulsing dots and dimming are now possible.