relays

what is a relay? an electrically controlled switch: energize the coil and the contacts move. great for isolating logic from higher voltages/currents.

driver circuit (logic → relay)

• use a transistor/MOSFET to drive the coil; microcontroller pins alone can’t.
• flyback diode across the coil (stripe to +) to catch the spike.
• pick coil voltage to match your rail (5/12 V) and contacts rated above your load.

contact types

• SPST / SPDT / DPDT — “NO” = normally open, “NC” = normally closed.
• keep mains far from logic; respect creepage/clearance.