Hey guys, brand new here, and relatively new to electronics and breadboard / prototyping. In fact, this is the first prototype I’ve ever done with Arduino…but I’m enjoying it, gathering up things from around the house and trying to solve invented problems.
I have two questions, one of them harder than the other probably.
- If you look at the included picture, I have 2 x 12-240 AC/DC relays. (Crouzet MUR3), the pole connected to the yellow jumper is a single wire to fire the relay. I’ve tried to fire this relay at 9v (was probably closer to 7v) and the relay will click quickly like it cant quite fire. Triggering the relay at 12v is no problem, and this works great.
Question Is: My Arduino cant pump 12v out of one of its digital/analog ports if it’s only being supplied 9 volts per the running power supply through the PSM, unless I step the voltage up somehow? How do I fire off a 12volt relay from an Arduino running at 5v?
Note: This Arduino is a MEGA 2560, but it’s been adapted on the underside to have 25 or so 3 pin servo plugs, and a battery holder for 2x 3.7volt lithium batteries (for use in a kids toy project). I’m repurposing this Arduino, but I’ve also got a stock 2560 available, and an UNO if there’s an issue with using this one.
My research tells me this:
1.) I can use a transistor as a switch, and can get 12v to the trigger pole from the original supply on command from the Arduino I/O. I understand the idea, I have NO idea how to make that work.
2.) Power the Arduino from the 12v supply…would this give me 12v available to trigger the relay through the I/O? I don’t need to power the relay from the Arduino, I’ve got that being powered by a 12v power supply.
I would also like a LED to illuminate when the relay is triggered. (So for the 6 seconds the relay stays open, per its internal program). - but I’ve burned a few LED’s out…which I guessed I would. How would I safely power the LED from the 12v output from the relay?
Thank you in advance everyone. I’m doing my best to learn all this, and teach myself practical, and text book knowledge. If I had unlimited hardware to melt down, I’d probably figure it out? I don’t so I’d like to do it without melting parts down. 
