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I am trying to build a (capacitive) moisture sensor with ESP-01S, my goal is to measure the soil moisture level, send it via wifi to a server (estimating 10-15sec execution time) and finish it off with deep sleep (for maximum time so around an hour). I tried drawing schematics of the circuit with two versions, with and without a voltage regulator. However, I have some questions.

I was thinking about choosing this battery Lifepo4 3.2V 1800mAh, which has a nominal voltage of 3.2V, end-of-charge voltage 3.65V (0.05 above the recommended rated V for ESP-01S), end-of-discharge voltage 2.0V. OR about this one XTAR 18650 2200mAh (slightly higher capacity) but it has a nominal voltage of 3.6-3.7V and I am afraid it therefore could go higher when fully charged.

Q1: Which is a better choice? The Lifepo4 where I would theoretically not need a regulator or the XTAR where I would probably need one?

Q2.1: When using a voltage regulator, what is the point of capacitors? Would it be possible to just use the voltage regulator without the capacitors?

I found this online:

The regulator doesn’t need an output capacitor; it is stable without one. The only reason you might want an output capacitor is to improve its transient response.

Seems like it should make the output more stable.

Q2.2: Does adding the voltage regulator decrease the efficiency in terms of how long it can power the whole thing? I will be putting the ESP-01S into deep-sleep and I know I will have to do a little "hack" for it to wake up from it.

Version without voltage regulator:

without voltage regulator

Version with voltage regulator:

with voltage regulator

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Neither is a good choice for a WiFI sensor that requires a stable 3.3V and at least 250mA.

Define your goals first then energy source, then voltage regulation and choose better parts.

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  • \$\begingroup\$ I made an edit and described my goal briefly. I was looking at declared power consumption and it said it can go up to 170mA (at most) and 10 µA in deep-sleep. I thought it would average maybe somewhere between 120-150mA, but I noticed now it does say a power supply with at least 250mA. I tried calculating the consumption via this it said roughly 200days so I thought I was safe. Also what do you mean "better parts" ? \$\endgroup\$
    – Matis
    Commented Mar 11, 2022 at 8:38
  • \$\begingroup\$ You never choose a power supply that runs at 100% max and never use a battery with a 1.2V swing for a chip that requires 5% stability (10% worst case) so you need better specs and design of selected parts. \$\endgroup\$
    – Tony Stewart EE75
    Commented Mar 11, 2022 at 13:43

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