New to Arduino. Have a project that involves three relay shields (Vellman 100 + (3) Vellman 400's. Question: How best to power up all (4) boards. Do I use a Wall Wart and run to each board in parallel, or do I power up the Arduiino Uno and then daisy chain the +5 V dc to each of the (3) relay shields? Or does it matter which.

DTS USA, Reading MA Sept 17, 2017

Not enough real info to give a 100% answer however each shield will require (from the sounds of it) an adequate supply in terms of current.

Not familiar with the Velman series (although they tend to be high quality) to say exactly.

If your supply has enough current you can daisy chain. Relays tend to draw a little more in that regard so better to ensure there is a little more than required.

Also beware of any jumpers / bridges that may need to be made before trying to power up. That will avoid any possible damage to an Arduino in terms of the voltage regulator etc.