A few words in advance...
Components are usually soldered onto a circuit board in height order, shortest first. This allows you to flip the board and have the component rest on
the table with the board on top of it. Otherwise, when you flip the board for soldering, the board will rest on the taller components and the shorter
ones will just fall out.
The downside of this method is that you have to assemble the entire board before testing. If you made a mistake, it can then be hard to find.
In this tutorial, we are attaching components grouped by functionality instead. We will then test each section separately. When attaching compo-
nents with long legs, just bend them so they stay attached when you flip the board. You can use masking tape to keep other components in place
while soldering.
Many features of the board are optional. To use it as a 16x16 LED matrix driver only the ATMEGA328-MCU along with the anode and cathode multi-
plexers are required. The rest is optional:
• To use it as a clock you will need the DS1307 real time clock. With the battery backing, it will continue to keep time when disconnected from a
power supply.
• For automatic time updates you can add the DCF77 receiver. The time will update any time it receives a valid signal. The receiver can be left on
permanently (by using the jumper on the receiver terminal strip to connect P to -) or you can connect P to D and, which connects pin D13 on the
ATMEGA328-MCU to PON, and you can set the pin high to turn the receiver off when you like.
• If you have a stable 5-6 volt supply, (e.g., a USB power supply or batteries), then you can connect those directly to the voltage regulator. If you
want to use an external power supply, then you need to set up the voltage regulation section and then the board will be able to take 7-12 volt. By
the way, you can use the jumper next to the anode multiplexers („5V<->Vext”) to send the external voltage to the Darlington arrays to increase
the brightness of the LEDs. But this is for experts and is only briefly covered in this tutorial.
• You can add a photoresister to control the brightness of the display based on the ambient light level.
• You can add the FTDI port and ISP header to program the microcontroller.
• Finally: Instead of the DS1307 you can also use a Chrono-Dot or a DS3231N. Stack-L and Stack-R can be used to chain boards to power a larger
display. Neither is supported with the current word clock firmware but it wouldn‘t be that hard to add.