Will this fry my Arduino?

Other Hardware General Electronics
1

Hi,

I'm currently working on a project using a generic Songle relay (srd-05dc-sl-c) and i just noticed that each relay requires ~72mA to drive it. I realize that Arduino UNO can safely handle ~40mA on each GPIO pin.

Why are there so many tutorials telling you to connect this relay directly to your Arduino if it can't handle it? I made the mistake of hooking one up, and it seemed to work fine. I just realized I probably should have an external supply to drive these.

So is my math right? Am i missing something? And what do i need to convert the Arduino output into a useable signal for these relays to function?

Here is a link to the relay datasheet.

Thanks!

2

Always drive a relay with a driver.
examples:
MOS FET or BJT
ULN2803 or equivalent.

Make sure there is a fly back diode across the relays coil.

3

Most of those relays are found on little boards with drivers on them, such as

1200×900 178 KB

or these multi-relay boards

All of which can driven by Arduino output pins directly.
It is rare to see that relay driven separately. Use a simple transistor driver as LarryD suggested, NPN to pull the coil - to Gnd, or an N-channel MOSFET like AOI-514:

4

Thank you for the quick replies.

I see now that "modules" have built-in drivers on them. I did not have one physically on me so i just googled the specs for the relay.

Much appreciated!