Hi all!
I have a DIY electric motorbike, which runs a custom BMS system. It pings the pack voltage via MQTT when charging to HA.
The sensor config is as follows
I would like to convert this voltage to battery charge % if possible inside HA.
100% is 116.2V
0% 95.2V
The battery drain is more or less linear. Any assistance on how I can do this would be much appreciated. as always.
Have you considered using a template sensor.
template:
- sensor:
- name: "battery_sensor"
unique_id: "Battery Sensor"
state: >-
{% set voltage = states('sensor.3fazer_-_voltage') | float(0) %}
{{ ((voltage - 95.2) / 0.21) | int }}
This will give you the % in a truncated integer.
Thank you so much, worked perfectly.
You don’t need a template sensor. The MQTT sensor supports a value template.
- platform: mqtt
name: '3Fazer - Voltage'
state_topic: 'ev/3fazer'
value_template: "{{ ((value|float(0) - 95.2) / 0.21)|round(0) }}"
unit_of_measurement: '%'
Also using |int truncates the decimal, where as |round(0) will round to the nearest whole number.
e.g.
70.99|int = 70
70.99|round(0) = 71
Also thanks! I did like the seperation so I can monitor voltage as well.
Updated it to use round vs int and that has correct it showing 99% vs 100% at full charge. Thanks
Hi @tom_l
Possibly kind of dumb question - how did you get the value of ‘0.21’ in the example above?
I have a sensor where I measure mm, and want to find the percentage where min are 100 mm and max are 500 mm…?
From this data:
If given two points (x1,y1) (x2,y2) you can work out the equation for the line that passes through them:
y = mx + c
https://content.byui.edu/file/b8b83119-9acc-4a7b-bc84-efacf9043998/1/Math-2-11-2.html
So your two points (0%, 100mm) and (100%, 500mm) gives:
y = 0.25*x - 25
or
% full = 0.25*(x in mm) - 25
Damn, @tom_l 
Thanx ! 
I was thinking wrong;
My sensor range are 100 mm (full) to 500 mm (empty) to monitor a water tank.
In my case, when the states(sensor.water_level) = 100, it should show 100% and opposite, when at 500 it should show 0%.
How on earth should I calculate this?
To make it worse, I wanted to put this into a gauge. It worked well until I realized it was all opposite… duh…
Are you able to help on this?
Exactly the same way as in the link I provided above.
%full = -0.25*(x in mm) + 125
Could you please show me how you calculated the numbers?
Sorry, advanced math ain’t my strong side, I do electronics and ESP32 stuff (using a TOF to measure the distance to the water level) 
I am using slider (input_number) as the min & max can change (different tanks to monitor).
Initially I resolved it differently:
state: >-
{% set fill = states('sensor.tof_poc') | float(0) %}
{% set min = states('input_number.mm_min') | float(0) %}
{% set max = states('input_number.mm_max') | float(0) %}
{{ (((fill - min) * 100) / (max-min)) | round(0) }}
How am I going to put that advanced calculation - even the other way where 100 mm = 100% and 500 mm = 0%? And even bring into consideration the input sliders where min and max can change?
Think I’m about to give up this route and look for something else…
I did. Watch the video in the link I posted. It’s high school maths.
You could try this instead:
You cant use templates with it but it is easy to change the points config. Which really you should not have to once it is set up.
As a mental exercise for the points (0%, input_number.mm_min) and (100%, input_number.mm_max):
state: >-
{% set distance = states('sensor.tof_poc') | float(0) %}
{% set x1 = states('input_number.mm_min') | float(0) %}
{% set x2 = states('input_number.mm_max') | float(0) %}
{% set m = 100 / (x2 - x1) %}
{% set c = 100 - (m * x2) %}
{{ distance * m + c }}
this will work for any values of input_number.mm_min and input_number.mm_max
I actually got it with your example I’m passed 50, so I do not remember so much from math classes back in the days 
Interesting part - if I changed
{% set x1 = states('input_number.mm_min') | float(0) %}
{% set x2 = states('input_number.mm_max') | float(0) %}
to
{% set x1 = states('input_number.mm_max') | float(0) %}
{% set x2 = states('input_number.mm_min') | float(0) %}
I get the reversed % where 100mm are 100% and 500 mm are 0%.
Thank you so much @tom_l
Um no. All you have to do is change the input number values in the frontend using the sliders.
input_number.mm_min = 100
and
input_number.mm_max = 500
or
input_number.mm_min = 500
and
input_number.mm_max = 100
Will both work the way you want them to. That was the whole point of using input numbers in the template, so you don’t have to change the template.
I noticed that straight away… playing with both scenarios
Need to make sure this way of calculating stick to my brain
Thats my config. Works perfectly. 0.1m = 100%, 1.1m=0%
sensor:
- platform: ultrasonic
trigger_pin: 27
echo_pin: 26
unit_of_measurement: "%"
accuracy_decimals: 0
name: "Lenti esoviz tartaly"
update_interval: 10s
filters:
- calibrate_linear:
- 0.1 -> 100
- 1.1 -> 0
That appears to be ESPHome configuration. Not Home Assistant.
This was helpful for my setup.
Hello All
I am a beginner and I would like to convert a volume entity (mm) into % and I do not know how to do it. Can someone come to my aid by providing me with a code to perform this task please. Thank you all