Powering a small "electromagnet" directly from an Uno?

Projects General Guidance
1

I would like to hold a ball bearing in place with an electromagnet, and then set it free and let it roll down a tray.

So far I have a nice solenoid with an iron core from a scrapped 24V relay.

When I supply it with 5V, it is plenty strong enough for what I need.

Looking on the basic values, I think I could power it directly from the Uno.

  • measured resistance: 333 Ohm
  • measured current when powered from a 4.5V battery: 12 mA

I will of course put a reverse biassed diode across the solenoid to deal with the voltage spike when it is switched off.

I feel safe, but I've learned from experience, to be worried when that happens.
:grin:

Am I overlooking something?

2

I like to always put an transistor to control this type of devices. Something like this:

3

Yes you can drive that solenoid directly from an Arduino pin.

4

I agree with dc42, you can use it directly.
But please use two protection diodes ! From GND to output pin, and from output pin to 5V. The small 1N4148 is fast and can handle current peaks.

5

If its 333 ohm its only going to use 15 mA but only thing I don't like is the wire in these things is enamel paint and a used one could easily break down and short. Why not pop a npn 12 cents then to chance a uC thats 4 dollars.

6

Thanks to all of you!

I have a box of 2n2222 transistor, and if I was going to use it in a more permanent setup, I'd probably use one of those.
For some quick experiments, I'm willing to take the risk and keep everything as simple as possible.