FAQ #10

On my ESP8266 when I flash the sketch the LEDs light up, is this normal?

Yes it is normal for both DMA and UART to have this side effect.

The UART is used to program the ESP, both DMA and UART are using the low level hardware that is also used for serial/uploads; so this can happen. They are reacting to the serial data being sent across the wire and get fooled into thinking its something when its just code being flashed.

This can be a problem in your design if you normally only plan to power a subset of LEDs or never set them to a high brightness. Thus you may only provide a 5v power with enough amperage for half the strip maximum possible power draw.

Since the LEDs need 5v, when I prototype I usually run a switch that I can turn them off when I upload; and the final project just doesn't get flashed.

For a great solution for a finished design that gets flashed often, see this discussion.

NOTE: OTA (over the air) flashing should not cause this.
NOTE: Some have said that using the UART method causes less flashing.