Use this forum to chat about hardware specific topics for the ESP8266 (peripherals, memory, clocks, JTAG, programming)

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By eriksl
#16892 If you take the resistors (the sum, not the ratio between the resistors, that's fixed of course) to small, it will drain a lot of power (maybe too much) from the source, if you take them too large, the divider will be influenced too much by the impedance of the gpio pin, of which there is no exact data, which may yield a voltage above 3.3V destroying the input.
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By j0hncc
#16895 Aside from the electrical interface covered above, there is also the issue that GPIO2 suffers the same problem as GPIO0, that if your signal presents LOW to GPIO2 when the ESP powers up *or resets*, it will boot in a mode that will not run your application. If this is a showstopper for you (it has been for me in some cases) on ESP-01, and your application does not need serial I/O, you could use TX or RX instead. (GPIO1/GPIO3).

Cheers,
John