REST Api with 4 Relais shield

[tobiascapin]

Hi,
I want to create a REST service to control 4 relais.

I bought a Yun rev2 and a 4 relais board, then I started from this Bridge tutorial:
https://www.arduino.cc/en/Tutorial/Bridge

I just deployed the full REST example in the tutorial and started my board, but, the relay nr 1 (PIN 4) start flickering. I notice that connecting the board the RX/TX leds binks with the relay, but if I run the Yun without the relais board, it doesn't blink.

IMPORTANT UPDATE: The flickering problem happens only while ethernet cable is plugged or wifi guest is connected. And it happens also with an empty sketch. So it is not related to the tutorial sketch.

What I'm missing? Any idea?

[pylon]

A link to that 4 relay boards schematics would help!

[tobiascapin]

Sorry, I forgot to say that it is the original arduino shield:
https://store.arduino.cc/4-relays-shield

[pylon]

How do you power the Yun?

[tobiascapin]

By USB cable, can it be related?

[pylon]

It may be that the Yun together with the relay board draws more power than the USB is able to deliver (officially you may draw only 500mA). If the voltage drops then a bit to low the brown-out detection of the 32U4 might reset the board which can be responsible for the symptoms you see. Try powering the Yun with a 9V wall power supply that is rated at least 1A.