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I'm currently playing with a cheap $7 RC car from the toy store, and has just started out with arduino and electronics.

toy car electric motor

What is the purpose of the torus thingy with wire going around it, between the motor and power?

I could not measure any difference in current/voltage/resistance measuring before/after it in the circuit.

What does this thing do? And do I need it (or can I just ditch it and connect the engine straight to the arduino?

PS: should the digital out use a transistor to connect the circuit between engine and power source, or can this small of a 5v engine be powered simply by going through the digital pins?

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The toroidal coil is probably an EMI or noise filter of some sort.

It's unlikely the Arduino GPIO pins can supply enough current to run this 5V "engine". You will need some kind of buffer, amplifier or high-current switching transistor.

Hint: Power the "engine" from a 5 volt DC power supply, measure the current it draws under actual operating conditions, then repost your question with these numeric details.

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  • \$\begingroup\$ FYI. The term is "Common mode filter". \$\endgroup\$ – Sparky256 Aug 1 '16 at 20:16

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