Hi all

I am using an ESP8266 NodeMCU to drive a set of 7 relays.

The NodeMCU is a 3.3V device but can take 5V power via a USB plug.

The relay board can take the 3.3V pin logic as input but uses a 5V supply to power the relay coils. LOW = on.

Each relay can draw 70mA and I will usually only ever have 4 on at a time, but when the ESP8266 boots it lowers the signal on 6 of the pins so I could reach 420mA draw for the relays.

I have a 5V power supply that is rated for 550mA so this sounds perfect. What I want to do is power both the ESP8266 and the relay board with the same power supply.

Is there any risk to simply running the +5V and GND into the USB socket and to the relay board terminals?

 

Well you may experience transients from relay switching.You can try and see if switching 4 relays a a time reset the nodemcu.

If it happens put a 10uh-33uh and a cap to form a basic LC filter for the NodeMCU.

Relays are powered raw while the nodemcu from the LC filter.

Find a the LC filter schematic on wikipedia.

It's a low pass filter that should keep transients away from the NodeMCU.

I'd use 2 caps.1 beffier of 470uF or around that value,and a second ceramic one...if available around 1-10uF.(helps with HF noise and has a better ESR).