Created by Mark Troyer & Fons Janssen - 30 December 2016
This respository explains how to build an efficient low-power circuit that powers a micro-processor after the pressing of a momentary DASH-like button and then shuts off power to the micro-processor when done. The highlights of this circuit are as follows:
- Ideal for battery applications that consume no power when off.
- ESP8266 is boot strapped ON with click of momentary push button.
- ESP8266 completely turned OFF through Arduino ESP8266 software command
- Less than 0.5uA consumed while WeMos D1 Mini is powered off (leakage from PNP transistor)
- Open collector configuration workaround using Arduino IDE on ESP8266
- Hardware concept can be modeled around other 3.3v microprocessors.
The Bill of Materials are as follows:
- Wemos D1 Mini (ESP8266)
- BC638 PNP transistor
- 100 Ohm transistor
- Momentary switch
- Blue LED
- LiFiPO4 battery with voltage between 3.0 and 3.6v
While not explicitly supported on the ESP8266 in the Arduino IDE, this circuit uses a open collector configuration with the PNP transistor base to energize the ESP8266. The PNP Transistor will be boot strapped with the momentary button being pulled to ground. Once the ESP8266 starts, the open collector configuration will persist with the "pinMode(D5, OUTPUT); digitalWrite(D5, LOW);" commands, keeping the ESP8266 running.
When the processing on the ESP8266 is complete, the open collector can be closed with the "pinMode(D5, INPUT);" command. The Blue LED on D2 is only used to signal that the Wemos D1 Mini is energized.
Hardware Connections:
- 3.3v supply--transistor emitter
- transistor collector--3.3v on Wemos
- GND supply--GND on Wemos
- PNP transistor base--resistor--switch--GND.
- D5 pin linked to resistor--switch junction.
- D2 pin--Blue LED--GND