I have a HiLetgo NodeMCU device that operates a sensor. In the area where I want to mount the sensor device, there are no AC outlets, so the sensor device will have to be battery powered. Looking at the manual for the NodeMCU, I see that it has a 3.3 VDC input port. However, two AA alkaline batteries will only produce 3.0 VDC. It can also be powered via the microUSB port, but that expects 5.0 VDC and three AA alkaline batteries will only produce 4.5 VDC. Yes, I am an engineer and may be getting to detailed, but what would you suggest that I do?
What is the desired battery lifetime? Do you have some deep sleep implemented or is the MCU running all the time? If you are running all the time you will drain the batteries in hours
The 5V expected is going straight to LDO regulator that regulates it down to 3.3V. It will work fine with 4.5V. But as the battereis go down, the voltage will go down aswell…so nearly depleted AA cell will have 1.1V (3.3V in total) and the regulator won’t be able to maintain stable output (it needs some overhead voltage between output to input)
Btw if you test your specific unit you can usually go pretty down with the “3.3V” voltage. I tested some esp8266 and it was running fine down to 2.3V
Thanks - what you are saying is the the voltage can be below 3.3 VDC and the sensor device should still work.
The voltage isn’t the issue. The issue is how much power wifi uses. You’ll be changing batteries often if your device isn’t sleeping the majority of the time.
I would use an 18650 battery and a buck/boost converter set to 3,3V. That way, you can recharge the batteries (environmental and money friendlier) and have only one regulator between battery and MCU. But as others suggested, you need to implement some deep sleep, else you will be swapping the batteries faster than you can recharge the 2nd set.