Hello! Popular situation, I would like to make an IoT chip based on esp8266 (ESP-07 must be the one) I would like to power it from AA batteries of 3, standard configuration with ldo MCP1700. There are many projects like this, but I have not found enough information on what to do when the...

You have an ADC in the module - you can use it to measure the battery voltage (you will need a divider)- the rest in the software. You can even cut the power with one of the outputs.

. It will not damage itself. It can reboot and if the voltage goes lower it will shut down. . The datasheet note for the ESP8266 states: 2.5V ~ 3.6V. You already have . . Provided that this ADC is calibrated. The characteristics of this ADC in the ESP8266 are highly non-linear. . Yes.

Fortunately, we don't need a super accurate measurement. It's just a matter of finding out that the battery voltage has reached the value at which you need to go to sleep (light the [LOW BATTERY] lamp, etc).

. There is a link in my footer to a post with Kolban's book for ESP8266 attached. Well worth a browse. As for the battery voltage measurement circuit itself, there is an interesting project at the link below. It is better to measure this voltage via the ADC in the ESP at half the battery voltage. Added after 28 [minutes]: . Here you have an explanation

Just don't forget that the ADC range is up to 1V. So the divider would have to be quite a bit bigger....

. Actually in the bare ESP8266EX this will be the case and you have to be careful not to exceed the 1V value. In modules like Wemos or NodeMCU there is already an internal divider and then the range is up to 3V3.

There is no divider in the esp07 so you have to be careful as with the bare 8266.

It's not so bad, gentlemen, nothing will happen to you, the pin tolerates more than 3.3V, but the reading will be poor because the range is up to 1V, so voltages higher than 1V will already be a constant, probably max1024. Considering what the author wrote 3 batteries is 4.5V so the divider would have to go down to 0.8V

Well you have asked a basic question and I will add more. If I use an LDO it will not put the circuit to sleep at 3V on the battery but at least 3.5V.... You have to take into account the dropout from the stabiliser. So if he feeds the LDO with 3V, the esp will get 1.8V ... So that and behind the LDO below 2,6V- we put to sleep. Because the dropout on the battery will also be behind the LDO. Although I do not hide that there are better stabilisers but hard to find and more expensive dropout at 100mv level.

. Usually the batteries are replaced with new ones. For what reason do you want to cut the power ?

That's right, but if I'm not mistaken, by enabling the deep sleep function permanently (for manual reset), the RTC clock module continues to work which means that the board still needs a 3V power supply after all, and as I mentioned it may not work :/

Hello there General khoam Thank you for writing back, as always you are very helpful . Please forgive me, but I had to. Thank you also tos18 for your pertinent comments . Very important information, I would love to read the recommended book on the ESP8266 module, supplementing the information on resetting, disabling. Well I read the catalogue note (probably the latest one) and found out about the newer versions with the note EX (from 2.5V) however I thought that the older versions e.g. ESP-07 -01 do not have it I purchased a couple of ESP-07's from Ali because of the antenna, which I also want to do some research on as to range and power taken. The thing is, I don't see this note on the boards I bought, unless it's another thing I don't understand and the EX add-on doesn't introduce a lower power option, just the esp8266 version itself. Well I wanted to use the ESP-05 module with the ex annotation as a design enhancement later. Yes, I have read that I need to calibrate the measurement obtained from the voltage divider (I need to read up on the built-in resistor) I apologise for not being very accurate, however I have over a year to write my thesis and I am doing research, I am very pleased with the interest about this module on the forum (strangely the professors at my university have only heard a little about it 0.o for that we have stm32f429 boards that people can't grasp, and the detail that we won't even use a quarter of their power :/)

Jarzabek666 Are you proposing that the maximum voltage should be 0.8V? well i tested the values 200Kohm/45Kohm (for low current, maybe i will give even more) Is this for safety reasons or did I misunderstand? (since I could set 4.5V as 1V, the excess will be treated as 100% if the pin tolerates 3.3V)

This is how I suggested that the program should see higher voltages above 4.5V, because as far as ordinary batteries are concerned, one working battery has 1.6-1.7V or even 1.8V which would give us 5.4V. . Yes and you won't see it in the program that's the point, voltages higher than 4.5V it will already see as 4.5V with a 4.5/1V divider . With your 200/47Kohm divider there is quite a safety range as the supply would have to exceed 18V to damage the ESP. I mainly wrote this way so that you would see some spare in the program more. On the other hand, I don't know why you would bother with it if esp8266 has a power supply of 18V to damage ESP. I don't know why you bother if the esp8266 has a VCC voltage readout. see the ESP.getVcc() command....

. What if it doesn't manage to read the voltage with this method? This is already behind the LDO.

Whatever the combination, measuring the voltage directly at its source, i.e. the battery, is the safest way. In this way, you may also be tempted to measure the drop in this voltage as a function of time, i.e. to roughly determine the quality of the battery.

TvWidget I didn't know what could happen if the batteries discharge to a very low level, that the esp8266 gets below 2.5V As I mentioned this is an issue for an engineering paper and everything has to be right, I thought the chip could break down. I found out here that the chip has protection, i.e. it will first reset, then shut down. Initially I wanted to add a BMS with 18650 (cut off at 2.5V), given the LDO dropout, maybe before the chip itself? However, this is where two issues remain, either I add this BMS, just need to see how much current it draws during deep sleep operation, and if I don't use protection, I need to find information from the manufacturer or in some book that the circuit will react e.g. to 2V 1V ~0 and won't damage itself I need to read the datasheet note again carefully. Ps. I remember about full sleep, i.e. on maximum sleep, the chip will wake up after ~3.5h - the internal RTC clock is running With ESP.deepSleep(0) does it still work? it shouldn't in my opinion Jarzabek666 You have provided . That's quite a drop, in the catalogue note I saw ~ 178mV I checked it myself a while ago and at 3V input I got 2.5V at 70mA (motor) (I didn't have such a large capacitor, I used a smaller one, the kit is already coming to me) Did I miss a pattern? Thank you all again very much for your interest .

Sorry, I didn't read that it was an MCP1700, I thought it was a standard LM1117.

Too low a voltage will not damage the circuit. You do not need to worry about this. You should, however, consider whether frequent resets will cause any problems due to the functionality of the device.

. The RTC and some of the memory associated with it works, but if you use ESP.deepSleep(0) then the RTC itself will not wake up the chip. According to the documentation: To put the ESP8266 in deep sleep mode, use ESP.deepSleep(uS) and pass as argument sleep time in microseconds. GPIO 16 must be connected to reset (RST) pin so the ESP8266 is able to wake up. . Specifying a value of 0 in ESP.deepSleep() will result in this being treated as 'infinite' time and the chip can only be woken up by reset. This is explained in detail at the following link: The attached manufacturer's document describes the sleep modes in detail. The examples given are based on ESP-IDF commands, but you can also use them with Arduino HAL.

ESP8266 (ESP-07) Power Management with AA Batteries and BMS Chip Integration

Dawidixxx 3192 20

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Can an ESP8266 ESP-07 running from AA batteries safely keep operating down to 2.5 V, or should I add a cutoff circuit around 3 V to protect it?

You do not need a 3 V cutoff to protect the ESP8266; the chip is specified for about 2.5 V to 3.6 V, and if the voltage drops lower it may reset and then shut down rather than damage itself [#18355965][#18357571] For a battery-powered design, measure the battery with the ESP’s ADC through a voltage divider and handle the low-battery decision in software, or switch the power off with a GPIO [#18355953] On a bare ESP-07/ESP8266 the ADC input range is only up to 1 V and there is no built-in divider, so the divider must scale the battery voltage accordingly; NodeMCU/Wemos boards already include that divider [#18356134][#18356382][#18356402] If you use `ESP.deepSleep(0)`, the RTC state remains, but the chip will not wake itself and must be reset to resume [#18357641]

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#1 18355924 22 Dec 2019 22:32

Dawidixxx Dawidixxx

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18355924 22 Dec 2019 22:32

Hello!
Popular situation, I would like to make an IoT chip based on esp8266 (ESP-07 must be the one)
I would like to power it from AA batteries of 3, standard configuration with ldo MCP1700.
There are many projects like this, but I have not found enough information on what to do when the batteries run down.

The common answer? When the chip measures that there is a min of 3v on the battery, it goes to sleep permanently.
This is a nice solution, but not enough for me, so I wanted to use a BMS chip from 18650 cells (along with sleep at 3v)
they cut off the voltage at ~2.5V however this is half less than the minimum spec note states (3V-3.6V)
I think the internal RTC counter itself can handle this 2.5V, until cut off by the BMS, however the point is that this is supposed to be part of an engineering job,
so you know, everything has to be proven to work :/ Is there any cheap circuit from Ali that will cut my voltage at 3V?
Or is there information somewhere that the circuit won't fail at 2.5V?

I'm really asking for your help, as I really liked these microcontrollers, and would like to build my circuits with the confidence that they will all work .

(Eventually I could use a module from esp8266ex, but for some reasons I don't want to use them yet)

Best regards David!
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#2 18355953 22 Dec 2019 22:45

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18355953 22 Dec 2019 22:45

You have an ADC in the module - you can use it to measure the battery voltage (you will need a divider)- the rest in the software. You can even cut the power with one of the outputs.
#3 18355961 22 Dec 2019 22:51

Dawidixxx Dawidixxx

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18355961 22 Dec 2019 22:51

That's right, but if I'm not mistaken, by enabling the deep sleep function permanently (for manual reset), the RTC clock module continues to work
which means that the board still needs a 3V power supply after all, and as I mentioned it may not work :/
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#4 18355965 22 Dec 2019 22:54

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Dawidixxx wrote:
And maybe there is information somewhere that the chip will not damage at 2.5V?
.
It will not damage itself. It can reboot and if the voltage goes lower it will shut down.

Dawidixxx wrote:
they cut the voltage at ~2.5V however, this is half as low as the minimum datasheet note states (3V-3.6V)
.
The datasheet note for the ESP8266 states: 2.5V ~ 3.6V.

Dawidixxx wrote:
I could use the module with esp8266ex

You already have .

tos18 wrote:
In the module you have an ADC - you can use it to measure the battery voltage
.
Provided that this ADC is calibrated. The characteristics of this ADC in the ESP8266 are highly non-linear.

Dawidixxx wrote:
if I am not mistaken by enabling the deep sleep function permanently (for manual reset),the RTC clock module continues to operate
.
Yes.
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#5 18355975 22 Dec 2019 23:00

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18355975 22 Dec 2019 23:00

khoam wrote:
Provided this ADC is calibrated. The characteristics of this ADC in the ESP8266 are strongly non-linear.

Fortunately, we don't need a super accurate measurement. It's just a matter of finding out that the battery voltage has reached the value at which you need to go to sleep (light the [LOW BATTERY] lamp, etc).
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#6 18355994 22 Dec 2019 23:13

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18355994 22 Dec 2019 23:13

Hello there
General khoam
Thank you for writing back, as always you are very helpful .
Please forgive me, but I had to.

Thank you also tos18 for your pertinent comments .

Very important information, I would love to read the recommended book on the ESP8266 module, supplementing the information on resetting, disabling.

Well I read the catalogue note (probably the latest one) and found out about the newer versions with the note EX (from 2.5V) however I thought that the older versions e.g. ESP-07 -01 do not have it
I purchased a couple of ESP-07's from Ali because of the antenna, which I also want to do some research on as to range and power taken.
The thing is, I don't see this note on the boards I bought, unless it's another thing I don't understand and the EX add-on doesn't introduce a lower power option, just the esp8266 version itself.
Well I wanted to use the ESP-05 module with the ex annotation as a design enhancement later.

Yes, I have read that I need to calibrate the measurement obtained from the voltage divider (I need to read up on the built-in resistor)

I apologise for not being very accurate, however I have over a year to write my thesis and I am doing research,
I am very pleased with the interest about this module on the forum (strangely the professors at my university have only heard a little about it 0.o
for that we have stm32f429 boards that people can't grasp, and the detail that we won't even use a quarter of their power :/)
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#7 18356014 22 Dec 2019 23:52

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Dawidixxx wrote:
Very important information, I would be happy to read the recommended book on the ESP8266 module, supplementing the information on resetting, disabling.
.
There is a link in my footer to a post with Kolban's book for ESP8266 attached. Well worth a browse.

As for the battery voltage measurement circuit itself, there is an interesting project at the link below. It is better to measure this voltage via the ADC in the ESP at half the battery voltage.
https://github.com/hallard/Battery-Voltage-Measure

Added after 28 [minutes]: .

Dawidixxx wrote:
The point is that I don't see this note on the boards I bought, unless this is another thing I don't understand and the EX add-on doesn't introduce the lower power option, just the esp8266 version itself.

Here you have an explanation
http://esp8266.net/
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#8 18356134 23 Dec 2019 05:44

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khoam wrote:
It is better to measure this voltage by the ADC in the ESP over half the range of the battery voltage.

Just don't forget that the ADC range is up to 1V. So the divider would have to be quite a bit bigger....
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#9 18356382 23 Dec 2019 10:45

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Jarzabek666 wrote:
Just don't forget that the ADC range is up to 1V. So the divider would have to be quite a bit bigger...
.
Actually in the "bare" ESP8266EX this will be the case and you have to be careful not to exceed the 1V value. In modules like Wemos or NodeMCU there is already an "internal" divider and then the range is up to 3V3.
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#10 18356402 23 Dec 2019 10:54

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18356402 23 Dec 2019 10:54

There is no divider in the esp07 so you have to be careful as with the bare 8266.
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#11 18356445 23 Dec 2019 11:20

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18356445 23 Dec 2019 11:20

It's not so bad, gentlemen, nothing will happen to you, the pin tolerates more than 3.3V, but the reading will be poor because the range is up to 1V, so voltages higher than 1V will already be a constant, probably max1024.

Considering what the author wrote 3 batteries is 4.5V so the divider would have to go down to 0.8V
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#12 18356969 23 Dec 2019 16:36

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18356969 23 Dec 2019 16:36

Jarzabek666 Are you proposing that the maximum voltage should be 0.8V?
well i tested the values 200Kohm/45Kohm (for low current, maybe i will give even more)
Is this for safety reasons or did I misunderstand? (since I could set 4.5V as 1V, the excess will be treated as 100% if the pin tolerates 3.3V)
#13 18357069 23 Dec 2019 17:15

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18357069 23 Dec 2019 17:15

This is how I suggested that the program should see higher voltages above 4.5V, because as far as ordinary batteries are concerned, one working battery has 1.6-1.7V or even 1.8V which would give us 5.4V.

Dawidixxx wrote:
since I could set 4.5V as 1V, the excess would be treated as 100%
.

Yes and you won't see it in the program that's the point, voltages higher than 4.5V it will already see as 4.5V with a 4.5/1V divider

Dawidixxx wrote:
Is this for safety reasons or did I misunderstand?
.

With your 200/47Kohm divider there is quite a safety range as the supply would have to exceed 18V to damage the ESP. I mainly wrote this way so that you would see some spare in the program more.

On the other hand, I don't know why you would bother with it if esp8266 has a power supply of 18V to damage ESP. I don't know why you bother if the esp8266 has a VCC voltage readout. see the ESP.getVcc() command....
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#14 18357282 23 Dec 2019 19:01

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18357282 23 Dec 2019 19:01

Jarzabek666 wrote:
But on the other hand, I don't know why you bother with this if esp8266 has a VCC reading. bother with it since the esp8266 has a VCC voltage readout. see command ESP.getVcc()...
.
What if it doesn't manage to read the voltage with this method? This is already behind the LDO.
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#15 18357327 23 Dec 2019 19:28

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18357327 23 Dec 2019 19:28

Well you have asked a basic question and I will add more. If I use an LDO it will not put the circuit to sleep at 3V on the battery but at least 3.5V.... You have to take into account the dropout from the stabiliser. So if he feeds the LDO with 3V, the esp will get 1.8V ...

So that and behind the LDO below 2,6V- we put to sleep. Because the dropout on the battery will also be behind the LDO.

Although I do not hide that there are better stabilisers but hard to find and more expensive dropout at 100mv level.
#16 18357346 23 Dec 2019 19:37

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18357346 23 Dec 2019 19:37

Whatever the combination, measuring the voltage directly at its source, i.e. the battery, is the safest way. In this way, you may also be tempted to measure the drop in this voltage as a function of time, i.e. to roughly determine the quality of the battery.
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#17 18357429 23 Dec 2019 20:12

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18357429 23 Dec 2019 20:12

Dawidixxx wrote:
There are many such projects, but I have not found enough information on what to do when the batteries run down.
.
Usually the batteries are replaced with new ones. For what reason do you want to cut the power ?
#18 18357507 23 Dec 2019 20:40

Dawidixxx Dawidixxx

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18357507 23 Dec 2019 20:40

TvWidget I didn't know what could happen if the batteries discharge to a very low level, that the esp8266 gets below 2.5V
As I mentioned this is an issue for an engineering paper and everything has to be right, I thought the chip could break down.
I found out here that the chip has protection, i.e. it will first reset, then shut down.

Initially I wanted to add a BMS with 18650 (cut off at 2.5V), given the LDO dropout, maybe before the chip itself?
However, this is where two issues remain, either I add this BMS, just need to see how much current it draws during deep sleep operation,
and if I don't use protection, I need to find information from the manufacturer or in some book that the circuit will react e.g. to 2V 1V ~0 and won't damage itself
I need to read the datasheet note again carefully.
Ps. I remember about full sleep, i.e. on maximum sleep, the chip will wake up after ~3.5h - the internal RTC clock is running
With ESP.deepSleep(0) does it still work? it shouldn't in my opinion

Jarzabek666 You have provided
Jarzabek666 wrote:
So if it powers the LDO with 3V then the esp gets 1.8V ...
.
That's quite a drop, in the catalogue note I saw ~ 178mV
I checked it myself a while ago and at 3V input I got 2.5V at 70mA (motor)
(I didn't have such a large capacitor, I used a smaller one, the kit is already coming to me)
Did I miss a pattern?

Thank you all again very much for your interest .
#19 18357563 23 Dec 2019 21:02

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18357563 23 Dec 2019 21:02

Dawidixxx wrote:
This is quite a drop, in the catalogue note I saw ~ 178mV

Sorry, I didn't read that it was an MCP1700, I thought it was a standard LM1117.
#20 18357571 23 Dec 2019 21:04

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18357571 23 Dec 2019 21:04

Too low a voltage will not damage the circuit. You do not need to worry about this. You should, however, consider whether frequent resets will cause any problems due to the functionality of the device.
#21 18357641 23 Dec 2019 21:38

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18357641 23 Dec 2019 21:38

Dawidixxx wrote:
Ps. I remember about full sleep, i.e. on maximum sleep, the circuit will wake up after ~3.5h - the internal RTC clock is running
With ESP.deepSleep(0) does it still work? it shouldn't in my opinion
.
The RTC and some of the memory associated with it works, but if you use ESP.deepSleep(0) then the RTC itself will not wake up the chip. According to the documentation:

To put the ESP8266 in deep sleep mode, use ESP.deepSleep(uS) and pass as argument sleep time in microseconds. GPIO 16 must be connected to reset (RST) pin so the ESP8266 is able to wake up. .

Specifying a value of 0 in ESP.deepSleep() will result in this being treated as 'infinite' time and the chip can only be woken up by reset. This is explained in detail at the following link:
https://diyprojects.io/esp8266-deep-sleep-mode-test-wake-pir-motion-detector/

The attached manufacturer's document describes the sleep modes in detail. The examples given are based on ESP-IDF commands, but you can also use them with Arduino HAL.

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✨ The discussion revolves around powering an ESP8266 (ESP-07) module using AA batteries and integrating a Battery Management System (BMS) chip. The user seeks to manage battery voltage effectively, particularly when the batteries deplete. Common advice suggests using the module's ADC to measure battery voltage, but concerns arise regarding the minimum operating voltage of the ESP8266, which is typically 3V. The integration of a BMS that cuts off at 2.5V is debated, as it may not align with the ESP8266's specifications. Suggestions include using a voltage divider for ADC readings, ensuring the LDO dropout is considered, and exploring the use of deep sleep modes to conserve power. The importance of measuring voltage directly at the battery source is emphasized, along with the potential risks of frequent resets due to low voltage.
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ESP8266 (ESP-07) Power Management with AA Batteries and BMS Chip Integration

FAQ

TL;DR: ESP8266EX runs at 2.5–3.6 V; "It will not damage itself" if AA voltage dips. Measure battery via ADC with calibration, then use deep sleep; RTC continues running. [Elektroda, khoam, post #18355965]

Why it matters: For makers powering ESP-07 from AA cells, this FAQ shows how to set safe low-battery behavior without extra BMS chips.

Quick Facts

ESP8266EX operating range: 2.5–3.6 V; undervoltage causes resets/shutdown, not damage. [Elektroda, khoam, post #18355965]
ESP-07/“bare” ESP8266 ADC range is 0–1.0 V; Wemos/NodeMCU add a divider for ~0–3.3 V. [Elektroda, khoam, post #18356382]
Deep sleep: RTC stays on; ESP.deepSleep(0) = “infinite” sleep; wake via GPIO16 wired to RST. [Elektroda, khoam, post #18357641]
Typical single‑cell BMS cutoff ≈ 2.5 V, similar to ESP8266’s lower operating edge. [Elektroda, Dawidixxx, post #18355924]
ESP.getVcc reads VCC after your LDO; use a resistor divider to read the actual battery. [Elektroda, khoam, post #18357282]

Will the ESP-07 get damaged if voltage falls below 2.5 V?

No. The ESP8266 will typically reboot, and if voltage drops further it shuts down. “It will not damage itself.” Design your firmware to handle brownouts cleanly. Add logic to enter deep sleep when the measured pack voltage hits your threshold. [Elektroda, khoam, post #18355965]

What cutoff voltage should I aim for with three AA cells?

A common practice is to enter permanent deep sleep around 3.0 V pack voltage. That preserves the batteries and prevents brownout loops. Implement the threshold in software using the ADC and a divider, as hardware BMS isn’t strictly required for chip safety. [Elektroda, Dawidixxx, post #18355924]

How do I measure AA battery voltage on ESP-07 safely?

Use the on‑chip ADC with a resistor divider sized so the ADC pin never exceeds 1.0 V at the highest expected battery voltage. ESP-07 lacks an internal divider, so wire an external divider to TOUT and calibrate in software. [Elektroda, khoam, post #18356382]

Is the ESP8266 ADC linear and should I calibrate readings?

Calibrate it. The ESP8266 ADC is notably non‑linear, so map readings against known voltages before using thresholds. A simple calibration table or fit is enough for low‑battery detection. “The characteristics of this ADC in the ESP8266 are highly non‑linear.” [Elektroda, khoam, post #18355965]

Can the ESP8266 cut its own power when the battery is low?

Yes. Measure the pack with the ADC, then use a GPIO to drive a P‑MOSFET or load switch that disconnects the supply. You can also just enter deep sleep and rely on minimal current draw, depending on your design goals. [Elektroda, tos18, post #18355953]

Is ESP.getVcc enough to monitor batteries behind an LDO?

No. ESP.getVcc measures VCC after your regulator, so it doesn’t show true battery voltage. If you want accurate pack readings and thresholds, measure at the battery with a divider into TOUT. [Elektroda, khoam, post #18357282]

Does the ESP-07 include an internal ADC divider like NodeMCU/Wemos?

No. ESP-07 has no internal divider, so treat it like a bare ESP8266EX. Keep the ADC pin at or below 1.0 V using an external resistor divider. [Elektroda, tos18, post #18356402]

How should I size the divider for fresh AA cells?

Design for fresh cells up to about 1.6–1.7 V each (≈5.4 V for three). Choose resistor values so 5.4 V maps to 0.8–1.0 V at TOUT, giving headroom and full-scale resolution. Verify with a DMM and adjust in firmware. [Elektroda, Anonymous, post #18357069]

What happens if the ADC input exceeds 1.0 V on ESP-07?

The ADC reading saturates near its maximum code (≈1024), and you lose measurement accuracy. Ensure your divider always keeps the TOUT voltage within range across operating and fresh-battery conditions. [Elektroda, Anonymous, post #18356445]

How do I implement a low-battery cutoff without a BMS?

Three steps:

Add a resistor divider from the battery to TOUT and read it in firmware.
Compare the calibrated reading to your cutoff threshold.
Drive a GPIO to open a P‑MOSFET/load switch or enter deep sleep. This approach avoids extra BMS hardware. [Elektroda, tos18, post #18355953]

What exactly happens in deep sleep, and how do I wake from “infinite” sleep?

In deep sleep the RTC and its memory keep running. ESP.deepSleep(0) requests an “infinite” sleep; only reset wakes the chip. To wake automatically after a set time, connect GPIO16 to RST and pass a microsecond interval. “Specifying a value of 0 ... ‘infinite’ time.” [Elektroda, khoam, post #18357641]

Do I need a BMS to protect the ESP8266 from undervoltage?

Not for the chip itself. Low voltage won’t damage it, but repeated brownout resets can affect device behavior. Prefer clean sleeps or a controlled cutoff using a GPIO and switch if your application requires stability. [Elektroda, TvWidget, post #18357571]

Why measure battery voltage at the source instead of after the regulator?

Measuring at the battery is safest and more informative. You can observe the voltage drop over time and infer cell quality. Post‑regulator readings hide battery sag and regulator dropout effects. [Elektroda, khoam, post #18357346]

Any recommended references for ESP8266 power and battery measurement?

See Kolban’s ESP8266 book for fundamentals, and the Battery‑Voltage‑Measure project for a practical divider design. Both are linked in the discussion and help you implement robust monitoring. [Elektroda, khoam, post #18356014]

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