Step 2: The DS1307 real time clock
Required parts:
Placing the parts:
As with the reset button you
must add on pull down resistors
(10 kOhm) to the H+, M+ and
Mode switches. If you forget
then those pins will hang and
the actions will constantly be
triggered. The DS1307 won‘t
work correctly since the time is
constantly being set.
2*4,7 kOhm
1*100 nF
1*clock crystal
1*DS1307
1*battery holder
and CR2032 battery
Make sure that the notch on the DS1307 lines up with the mark on the board.
Before soldering the battery holder, tin the round pad with the minus sign to make sure the battery makes a
good contact with the board.
The time crystal is soldered so that, when bent over, the housing will lie on the long rectangular solder pad. In
contrast to the crystal next to the ATMEGA328-MCU, here we do need the ground plane (Those interested in
the details should google “dallas real time clock crystal considerations.) It is essential to solder the housing of
the crystal to the ground plane. Using additinal soldering flux helps here...
For testing purposes, if the clock is properly attached then the green LED will start blinking once per second
(after the initial three fast flashes).