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I want to make a switch which permanently cuts a power supply to a microcontroller when the supply voltage drops below a certain level.

I am powering an ESP32 development board from two 3.7V 18650 batteries. The board has a built-in AMS1117-3.3V regulator which regulates the voltage to the MCU at 3.3V. The microcontroller basically lives in deepsleep mode and just wakes up to send a byte of information to a server (hosted by an ESP8266 board) every hour. The problem that I am having is that there is no kill switch to turn off the microcontroller when the voltage gets too low. So the microcontroller just boots and fails continuously.

I know that you can turn off the MCU by pulling the ENABLE line low, but I need a switch to pull it low and remain in that state after being "tripped".

I hope it makes sense and I am open to any design ideas or alternatives that could work.

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    \$\begingroup\$ How permanent is permanently? \$\endgroup\$
    – Hearth
    Jun 16 '21 at 14:54
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    \$\begingroup\$ A microprocessor supervisor with a power-on-reset function is specifically designed for this and will cost you less than $1. \$\endgroup\$
    – vir
    Jun 16 '21 at 15:44
  • \$\begingroup\$ Like this: forum.digikey.com/t/… \$\endgroup\$
    – Kyle B
    Jun 16 '21 at 15:49
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    \$\begingroup\$ What releases the "lock" so the uC can star again? \$\endgroup\$ Jun 16 '21 at 15:57
  • \$\begingroup\$ @Hearth I want the trip switch to keep the ESP32 module off until the batteries are recharged (i.e. the voltage is above the limit at which it trips). \$\endgroup\$ Jun 17 '21 at 11:35

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