ESP8266 Community Forum

Hello everyone,

So I'm new to low-voltage circuitry and electronics in general. I've posted the below outline on Reddit and everyone is telling me I need a battery, but I'm not sure why given my constraints. Hoping for some clarification:

"I want to use JUST a solar panel to power an ESP-12F and a Capacitive Soil Moisture Sensor (CSMS). I dont mind if it doesnt run on a cloudy day, and it does not need to run overnight. [ie. a couple of readings a day in perfect circumstances would be sufficient]

I want the ESP-12F to wake from deep sleep check the soil moisture via an input on the A0. It will send the moisture level to a MQTT broker running on the same network, then go back into deep sleep. I'm aware that I will need to divide down the CSMS output (0-3v) to an ingest-able 0-1v for the A0 pin on the ESP-12F.

I figure I will need a 5v 150mA solar panel and a LDO voltage regulator to get a consistent 3.3v for the ESP and CSMS. I'm looking for recommendations on the above as well as pointing out any shortcomings of my design.

Thanks in advance!"

You're going to need some sort of storage other than just a solar cell - a supercap could work but even a cheap NiCd AAA cell might be fine. The initial startup causes a current spike that will drag a cell's voltage right down and it won't even start at 150mA - the wifi in Tx mode will be 120mA with bursts so you have to find a way to boost that up. 250mA peak is what you need to plan for.

I would also look at running the ESP and sensors at 2.8 volts - the ESP is good down to 2.6 volts. You'll need to find a moisture sensor that operates at that voltage though

I would look at a really efficient LDO, or a buck converter that can use the panel's extra voltage to produce extra current