Arduino-based master clock for schools

Step 8: Installation

If you are at all unsure about the safety precautions necessary when installing the new mater clock, you should probably consult an electrician.

The cleanest way to install the new master clock is to simply bypass the connections of the old master clock. For example, if there is a terminal on the old master clock that pulls to ground when the sync signal is "on", then connect this wire to the sync terminal of the new master clock. The other side of the sync terminal should  then be connected to ground so that when the relay connects the wire to the ground the same effect is achieved.

Alternatively, the relay terminals can be connected to a hot wire (120 or 24V AC depending on slave clock specifications)  and then to the sync wire. It really depends on the configuration of the existing system and how much you are willing to get your hands dirty.