GPIO15 is not broken out on the ESP-01. It exists internally, and it is already connected to ground.
david1234:
and where is GPIO2 - the one I can use?
It's right here:
Keep in mind that:
- GPIO1 and GPIO2 will burst out serial data on boot, this could damage your sensor.
- GPIO2 cannot be low at boot.
- GPIO0 cannot be low at boot, except during programming.
If you don't want to live with these restrictions, you could get a Wemos D1 mini for around $3.50.