Schematic design help.

Hello fellow arduino enthusiasts. I’m currently making a pcb that is a generic platform for most of my electrical projects. I’m creating a design that can have multiple outputs that will be 240v relays mainly. Therefore I need transistors that will control the 12v coil and diodes that will take the back emf when they are turned on so I don’t destroy my arduino or transistors. I’m also adding a pull down resistor so when the arduino is reset no state change will occur during start up. This is my schematic, is there anything else I should be adding on the output side? Anything that I have not considered. I’d hate to get it printed and not to work.


As this is going to be your prototyping PCB can I suggest you use your digital I/O for your relay outputs, and keep your A0 to A7 for any analog input you may need.

Your board needs to be versatile so place header pins at each I/O pin with jumpers so you can use them as Input or Output, you circuit has them being only output.

Also your “Active 12-20V” is going to the IC, it is only a 5V device.

Active 20V rewrite as 20Vdc+
Neutral 20V rewrite as gnd or 0Vdc.

Active and Neutral refer to AC mains, not DC.

A personal peeve, diagonal wires in schematics, looks like a rats/birds nest, use only vertical and horizontal.

Hi, what is your electronics, programming, arduino, hardware experience?

Tom… :slight_smile:

On schematic peeves, you have the Gnd along the top and supply along the bottom. Most think of Gnd as going along the bottom and supply going along the top.


very helpful input people thanks. especially the diode part. :).
after I posted this I actually started on the input side and realised that I did have it the wrong way round and spun the arduino around. Yes it is an arduino nano that is the microprocessor that is the brains of this project.

Great idea about the header pins. Like that idea.

I thought the Vin pin was before the onboard regulator therefore needed 6 - 20v? am I wrong about this?

My experience is pretty limited in the microprocessor world. I’m an electrician (hence the active neutral labeling). I have PLC programming experience but am new to C++.

True about the location of ground too. I’ll keep that in mind for next one. Not going to change if for this one.

Ive attached the updated one I’ve been working on. Let me know what you think.