ESP8266 Community Forum

- Sun Apr 10, 2016 10:12 am #45229

Hi Dachs,

The vehicle battery voltage has a range of about 9V to 16V. With all of the motors, solenoids, etc on that bus turning on and off, it is not a clean supply. When the loads turn on and off, voltage transients will occur.

The following circuit can be used to monitor the vehicle battery voltage with an ADC input. R1 and R2 divide the voltage from the 9V to 16V range to the 3.3V range of the ADC input. D1 and D2 clamp transients to the supply rails to limit the transient peaks to -0.6V and +3.9V. C1 provides a low pass filter and slows the transients. R3 limits the input current to the ADC input during a transient.

Vbatt ADC Input.JPG

If we are talking about ESP8266 Internal ADC, be careful, MAX ADC input range is about 1V depending on your VCC (more like a usual value of 0.978).

Last edited by trackerj on Mon Apr 11, 2016 3:22 am, edited 1 time in total.

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- Sun Apr 10, 2016 12:13 pm #45234 Trackerj,

That is good info, I have not used the ADC input of the ESP8266 and was not aware of the ~1V limit.
Assuming a 3.3V reference was my oversight.

- Mon Apr 11, 2016 10:26 am #45294 Thanks to everyone for your help. Yes, the ESP8266 ADC in is only ~1v, so I plan to stay just under that limit.

If you don't know what you are doing, the ODB port is not the place to start, you could possibly damage your on board computer.....

Thank you for your concern. It's not that I don't know what I'm doing, in general. I am just very new to the microcontroller board world and calculating electrical current and resistance. However, I will only be accessing 2 pins in the OBD port, 12v and gnd.

The vehicle battery voltage has a range of about 9V to 16V. With all of the motors, solenoids, etc on that bus turning on and off, it is not a clean supply. When the loads turn on and off, voltage transients will occur.

The following circuit can be used to monitor the vehicle battery voltage with an ADC input. ....

Thank you GregryCM, this look like exactly what I need. I will just need to change the resistors to something like R1 = 100k and R2 = 6.6k (3x2.2k in series?). I just need to pick up those capacitors and get up and running.

it might be a good idea to read my post about Internal ADC and Voltage Divider calculations

trackerj, reading your article is part of the reason I've gotten as far as I have.

- Tue Jun 19, 2018 2:16 am #76516

Hi Dachs,

The vehicle battery voltage has a range of about 9V to 16V. With all of the motors, solenoids, etc on that bus turning on and off, it is not a clean supply. When the loads turn on and off, voltage transients will occur.

The following circuit can be used to monitor the vehicle battery voltage with an ADC input. R1 and R2 divide the voltage from the 9V to 16V range to the 3.3V range of the ADC input. D1 and D2 clamp transients to the supply rails to limit the transient peaks to -0.6V and +3.9V. C1 provides a low pass filter and slows the transients. R3 limits the input current to the ADC input during a transient.

Vbatt ADC Input.JPG

Hi
I've been looking for a voltage divider like this but i would need to adapt it for 1V ADC. I tried to calculate but I can't come up with your way to calculate resistances in this setup.
Thanks!

WEMOS D1 Mini/Arduino