I want to use the SRD-05VDC-SL-C relay with my arduino. I was serching the web and saw that it is used on a board with an extra VCC Pin and the board also has resistors and a diode(like the one in this project: "http://www.circuitbasics.com/setting-up-a-5v-relay-on-the-arduino/" ). Can I use the relay without the board directly on my arduino like this: coil pin 1 on GND and coil pin 2 on a normal digital pin? Or will I need to use those boards because of the "high" power(it will draw about 72.5mA)?
Hi genicki, welcome.
You can’t directly control relays with Arduino pins, period.
One of the reasons is the high current, which is way over the rated current for any Arduino pin.
But also there’s a thing called “rush-in current”; the current a part takes directly after being powered.
An inductive load like a relay coil or a motor, will briefly take 6 to 10 times the rated current.
Even for the very short time this happens, it will surely do serious damage to your Arduino.
Another thing to remember, is to absolutely have a diode (in reverse) across the relay coil, because that coil will kick back when you de-energise it.
There’s a lot to be said about relays, but i think you might like to read what has already be said for instance on wikipedia (click !).
I haven’t read all of that myself, but i’m sure it’ll teach you a thing or two about relays you didn’t know yet.
The short version:
Use the modules, and power them from a different supply.
Use circuit Q3, you would of course need to use 5v instead of the 12v shown.
Note, the relay boards also include an opto isolator.