ESP8266 Community Forum

- Wed Mar 15, 2017 3:49 pm #63748 That is perfectly acceptable as well. The point is to have two inverter stages. So that a high state (reset state) is also the off state for the relay.

I tend to use transistors because they were the cheapest switches for ages.



R3 is optional as long as the internal pull up resistor is enabled at reset.

- Wed Mar 15, 2017 5:19 pm #63753 Original post says that external pull down didn't work. That sounds strange to me.

I find that pull ups are around 36K as measured on an ESP-12. An external pull down of 3.3K gives a default voltage of 0.27V before the sense of the pin is defined which is well below threshold turn on of any relay driver.

This is borne out by check measurements I took. I also checked with a scope and there were no unexpected transients.

- Wed Mar 15, 2017 8:31 pm #63757

Why not relying on the fact that PullUp can secure the OFF state instead and bringing GPIO to LOW to turn ON the relay ?

in that case when esp8266 is off, gpio is low and relay will be on.
I don't want the state of the relay to change when esp8266 restarts. I need default state of the relay to be off. unless my esp8266 board is connected to power and esp8266 is operating properly and running my code.

- Wed Mar 15, 2017 8:36 pm #63758

That is perfectly acceptable as well. The point is to have two inverter stages. So that a high state (reset state) is also the off state for the relay.

I tend to use transistors because they were the cheapest switches for ages.



R3 is optional as long as the internal pull up resistor is enabled at reset.

I will give this a try using a npn and pnp transistors. Thank you.
Do you have any suggestions on resistors value? my relay is also 3v3

edit:
in your suggestion, the relay state changes if the whole circuit loses power, right?