- What is Relay?
Relay Shield is just a switch, if you set a HIGH level to the relay pin, the relay would turn to the NO position, so the circuit is intact between NO and COM. And if you set a LOW level to the relay pin, the relay would turn to the NC position, so the circuit is intact between NC and COM.
So the voltage of relay pin is a Start Voltage, and the 9v is a Operation Voltage, but none of voltage flow between the pin of Relay(NC,NO,COM) without plugging external circuit into it.More information you can refer to the schematic of Relay Shield.
Please refer http://seeedstudio.com/wiki/Relay_Shield_V1.0#Interface_Function
1. Connect external 9V DC power supply through the Jack pin
2. Use any two of the four Relay terminals for connecting DC motors:
COM2 - Common Pin of Relay 2 -----> Connect to DC 12V
NO2 - Normally Open pin of Relay 2 --> Connect to + of motor
NC2 - Normally Closed Pin of Relay 2 ----> Do not connect
Connect GND pin of DC12V and GND of DC Motor
Similarly use COM3, NO3 to connect another DC motor.
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