How do I power an Arduino UNO + LEDs on same 12V external power without Vin


First time here so apologies if I make any mistakes forum decorum or electronics wise. I’m currently setting up a model that will have lights and sound. I will need to power the arduino, adafruit wave shield, and many LEDS off a 12v 3.7A power supply. I would normally use the Vin but it’s limited to 1 amp output and I will need more than that.

This is hopefully a basic question but how do I properly wire up the 12v 3.7A power supply to a series of LEDs and also power the Arduino? I will not have access to USB power for the Arduino. I have included a partial Fritzing diagram that includes one LED cluster and what I’m assuming the proper wiring is to power the arduino and the LEDS without using the Vin.

I’m using a 1k resistor after the TIP120/TO-220 MOSFET as the go between the 12v and arduino.

A TIP120 is a darlington, NOT a mosfet. It works, but the high saturation voltage will affect LED brightness and it will get hot. Better find a logic fet.

Your Fritzing diagram shows the collector and emitter connections reversed. Emitter goes to ground and collector (middle pin) goes to the LEDs.

It might be better to move the current limiting resistors to the +supply side of the LEDs. Try to avoid using pin13. It might flash during bootup.

Remove the black wire that goes to the top GND pin. Connect the green GND wire to emitter.

Correct your Fritzing diagram, and repost. Leo..

N-channel MOSFET, AOI-514.

Thanks for the response. I left the resistors on the other side because I already wired up the lights. Oops. In the future I will put them in the front.

I switched to input 12, thanks for the tip.

I got rid of the black ground and corrected the green GND wire to emitter. I had the black going to the top GND pin because I know I need to have the battery GND going to the Arduino GND. I now see connecting the green GND wire to the emitter base will also do that.

MOSFETs are not Darlingtons, got it. I have been instructed to use the TIP120 before and didn’t know that MOSFETS would work better. Crossroads, thank you for the link.

Regarding the power connections. Can I just splice the power source wires and run them to the board and arduino like I have shown in the diagram?

Yes. I can't tell if you have the anodes of the right hand LEDs connected to +12 or not, but that's what you need. Cathodes of left hand LEDs down to the transistor.

can i operate a 3~motor,220/380/440v,50/50/60Hz,2/1.2/1.2 A with 0.37/0.43kw..water pump via an 5v single Chanel relay module through a ir sensors ?...its for my poultry farm ..plz help me with this asap. if possible guide me with the wiring and coding as well...

CrossRoads, thanks again for the response. I really appreciate it.