ESP8266 Community Forum

- Thu May 07, 2020 10:58 am #86952 im curently making a simple switch my one issue is that when i connet my nodemcu to the power supply it wont run the code if my relay is connected to 3v3 or any power pin but if i start the nodemcu without the relay connected and after it boots i connect the relay it works fine any suggetions on how to fix this issue since its the only reason i cant solder and finish my project

- Mon May 11, 2020 10:18 am #87038 Some hints (since you didn't share any details with us):

• Don't connect a relay directly to a GPIO since it can only deliver around 12mA and a relay (almost) always need a multitude of that. Use a switching transistor in between.
• Don't connect a relay (or any low resistence component) to GPIO0, GPIO2 or GPIO15 (D3, D4 or D8 on the NodeMCU) since these are needed to properly boot the ESP.

Assumption is the mother of all f*ckups. At least: that's what I'm assuming.

- Mon May 11, 2020 12:02 pm #87039 also beware of using a pin that must be high on boot (D3 for example) as your relay circuit depending upon your design (a resistor and NPN transistor?) may have unwanted effects and affect the voltage on this pin.