Please note: Although this question tangentially involves a Raspberry Pi, this is really more just a pure robotics question at heart.
I'm trying to connect my Raspberry Pi 1 Model A to this buzzer. I've seen wiring diagrams of this in action, and believe I need to put a resistor in between the buzzer and the (3.3V) output GPIO pin. If this is incorrect, please begin by correcting me!
My question is: how do I calculate the required ohms of this resistor? This particular buzzer is rated at 6VDC.