Arduino Uno Fails to Start

Other Hardware General Electronics
1

Hey all, I'm looking for a little help on what should be a simple project.

I have an Arduino Uno hooked up to a 4 relay bank.

4 Relay Isolated Modules

The relay bank is driving driving 4 AC loads.

The Uno is powered by an AC adapter 9V DC 2A.

Relays are power via the Uno 5v regulator.

When I power up the system Uno/Relays/Motors together (power strip) occasionally the Uno doesn't start and all four of the relays all turn on together as these are active low relays. (Bad) I tried using a watchdog via wdt_enable(WDTO_2S); but this doesn't make the Uno restart from this condition. The watchdog works correctly when the Uno starts normally.

Ideas would be appreciated.

2

Do you have a multimeter to check if the 5V is holding up?

Have you tried running the Blink LED sketch (maybe with and without the relay board connected)?

Have you tried modifying the Blink LED sketch to address one of the I/O pins running a relay to "blink" (cycle) one of the relays?

3

A quick calculation tells me that the regulator of the Uno is dissippationg 1.25watt with four relays on.
Put a finger on the regulator. If you can see the shape of the regulator burned in your finger, it's too hot.
It will shut down from the extra ~350mA relay current (if you're lucky).
Leo..

4

kingofl337:
I have an Arduino Uno hooked up to a 4 relay bank.

Sounding bad!

kingofl337:
Relays are power via the Uno 5v regulator.

OK, that does it! Problem instantly resolved!

5

Too bad there's so many incorrect diagrams and advice on the web showing the wrong way to power up these modules.
Try this connection and power scheme (8 relay module shown).