A place users can post their projects. If you have a small project and would like your own dedicated place to post and have others chat about it then this is your spot.

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By teknohippie
#96057 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!"
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By davydnorris
#96058 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