I am relatively new to Arduino, and have been doing a project to trigger an LED/alarm when movement is detected to be over a certain threshold value. I am using an Arduino Uno, an LED/buzzer (https://www.adafruit.com/product/2994), an MPU-6050 (https://playground.arduino.cc/Main/MPU-6050), and a 4 channel relay board (http://www.seeedstudio.com/blog/2013/02/28/shield-evolution-flexible-add-ons-for-arduino/relay-shield/ - sorry it's not very descriptive).
The LED/buzzer needs a 12V DC power supply, and I am using a wall wart to supply it. I am wondering how I am supposed to hook everything up - everything online tells me that the LED needs to be connected not only to the relay board, but to a power supply as well. However, my power supply is to the Arduino itself.
Based on the following picture, I would think that I would need to take the ground wire of the LED to the power source itself, then connect the power source to the relay board Common input.
Here is the circuit without the external power, using a small LED:
And here is the current setup (note that the cables were initially shifted over by 1 on the analog input, but I have fixed that since):
Is there a way to use the wall wart as the power supply? Do I even need the relay board?