0
\$\begingroup\$

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

\$\endgroup\$

1 Answer 1

0
\$\begingroup\$

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.

\$\endgroup\$
2
  • \$\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\$ Commented Mar 11, 2022 at 13:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.