상황
A TTP223 capacitive touch sensor needs to switch a mains-powered AC appliance safely through a relay, with transistor drive and flyback protection.
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01
Use an NPN transistor to sink relay coil current from the TTP223 output
02
Keep AC and DC grounds isolated by using a separate neutral net
03
Include flyback diode across relay coil and fuse on live
Reuse for any low-voltage touch or control signal switching an AC load via relay.