esp8266 CH_PD useful for anything?

[ralphd]

I have ESP-01 and ESP-03 modules, both of which have CH_PD(aka CHIP_EN) broken out.  Has anyone seen CH_PD put to good use?  Since bringing it low completely powers down the chip including the RTC, it isn't even useful for implementing deep sleep.

[Muxr]

I have ESP-01 and ESP-03 modules, both of which have CH_PD(aka CHIP_EN) broken out.  Has anyone seen CH_PD put to good use?  Since bringing it low completely powers down the chip including the RTC, it isn't even useful for implementing deep sleep.

ESP-01 and ESP-03 were initially meant to be used as an Arduino WiFi module. In that aspect it made sense to break out CHIP_EN so that the user could disable the device when not in use (to save power).

Now that people have figured out how to replace the firmware on the module and run code on it there is little use for it.

[PaulB.]

Not at all useless!   

The notion that the ESP-01 - or indeed any ESP - was "meant to be used as an Arduino WiFi module" is really just a fantasy.    Arduinox are not the "be all and end all" and to imagine a chip manufacturer whether Microchip or Espressif would make something "for Arduino" is fanciful to say the least.   

While "deep sleep" uses very little power, pulling CH_PD LOW reduces this to zero - or would but for the 12k resistor on the ESP-01S, thus making that variant unsuitable for standby battery operation (275 µA draw).  You would instead need to use the ESP-03.

The point is that you completely control whether the chip (well, module) is turned on and drawing any power, by this pin which is a CMOS logic input.  That is the beauty of CMOS; turn it off and the power consumption is zero.

What you can do, operating the ESP at 3 V from two alkaline "AAA" or "AA" cells, is to hold CH_PD LOW with a resistor and pull it up with a pushbutton, then hold it HIGH via a diode from any available I/O which is not already pulled up by a resistor.  The ESP can then perform whatever WiFi task is necessary, when this is complete, pulling the controlling I/O LOW to disable itself completely (given that the button has been released) and using virtually no power until next required.