Added usermod "battery status basic" (wled#2127)

* added usermod battery_status_basic

* test.. something is wrong

* Squashed commit of the following:

commit 0f84552
Author: itCarl <[email protected]>
Date:   Tue Aug 10 18:35:15 2021 +0200

    updated readme and added image showing info modal

commit 055579f
Author: itCarl <[email protected]>
Date:   Mon Aug 9 20:53:07 2021 +0200

    small map function fix

commit 811614c
Author: itCarl <[email protected]>
Date:   Mon Aug 9 19:35:21 2021 +0200

    updated ui

commit cadf2e2
Author: itCarl <[email protected]>
Date:   Mon Aug 9 16:07:32 2021 +0200

    added usermod battery_status_basic

* updated readme, changed USERMOD_BATTERY_MIN_VOLTAGE default to 2.6 volt

* fixed readme image file naming

* added usermod settings for runtime changes

* fixed copy and paste mistake

* undo ui changes

* reworked addToJsonInfo() to make it compatible with the standard Info page.

* removed images from readme

* added ESP32 support

* updated readme

Author: itCarl

usermods/battery_status_basic/readme.md

@@ -0,0 +1,55 @@
+# :battery: Battery status/level Usermod :battery:
+
+This Usermod allows you to monitor the battery level of your battery powered project.
+
+You can see the battery level in the `info modal` right under the `estimated current`. 
+
+For this to work the positive side of the (18650) battery must be connected to pin `A0` of the d1mini/esp8266 with a 100k ohm resistor (see [Useful Links](#useful-links)).
+
+If you have a esp32 board it is best to connect the positive side of the battery to ADC1 (GPIO32 - GPIO39)
+
+## Installation
+
+define `USERMOD_BATTERY_STATUS_BASIC` in `my_config.h`
+
+### Define Your Options
+
+* `USERMOD_BATTERY_STATUS_BASIC`                   - define this (in `my_config.h`) to have this user mod included wled00\usermods_list.cpp
+* `USERMOD_BATTERY_MEASUREMENT_PIN`                - defaults to A0 on esp8266 and GPIO32 on esp32
+* `USERMOD_BATTERY_MEASUREMENT_INTERVAL`           - the frequency to check the battery, defaults to 30 seconds
+* `USERMOD_BATTERY_MIN_VOLTAGE`                    - minimum voltage of the Battery used, default is 2.6 (18650 battery standard)
+* `USERMOD_BATTERY_MAX_VOLTAGE`                    - maximum voltage of the Battery used, default is 4.2 (18650 battery standard)
+
+All parameters can be configured at runtime using Usermods settings page.
+
+## Important :warning:
+* Make sure you know your battery specification ! not every battery is the same !
+* Example:
+
+| Your battery specification table  |                 | Options you can define        | 
+| :-------------------------------- |:--------------- | :---------------------------- |
+| Capacity                          | 3500mAh 12,5 Wh |                               |
+| Minimum capacity                  | 3350mAh 11,9 Wh |                               |
+| Rated voltage                     | 3.6V - 3.7V     |                               |
+| **Charging end voltage**          | **4,2V ± 0,05** | `USERMOD_BATTERY_MAX_VOLTAGE` |
+| **Discharge voltage**             | **2,5V**        | `USERMOD_BATTERY_MIN_VOLTAGE` |
+| Max. discharge current (constant) | 10A (10000mA)   |                               |
+| max. charging current             | 1.7A (1700mA)   |                               |
+| ...                               | ...             | ...                           |
+| ..                                | ..              | ..                            |
+
+Specification from:  [Molicel INR18650-M35A, 3500mAh 10A Lithium-ion battery, 3.6V - 3.7V](https://www.akkuteile.de/lithium-ionen-akkus/18650/molicel/molicel-inr18650-m35a-3500mah-10a-lithium-ionen-akku-3-6v-3-7v_100833)
+
+## Useful Links
+* https://lazyzero.de/elektronik/esp8266/wemos_d1_mini_a0/start
+* https://arduinodiy.wordpress.com/2016/12/25/monitoring-lipo-battery-voltage-with-wemos-d1-minibattery-shield-and-thingspeak/
+
+## Change Log
+
+2021-08-15
+* changed `USERMOD_BATTERY_MIN_VOLTAGE` to 2.6 volt as default for 18650 batteries
+* Updated readme, added specification table
+
+2021-08-10
+* Created
+