artificial_adc_noise.md

Artificial ADC noise

atmel atmega32 cpu

The atmega32 ADC resolution is only 10bit and we are measuring a voltage span of 30V when measuring battery voltage, so the voltage resolution is about: 30V/1024 = 29mV. Cheali-charger is trying to enhance the ADC resolution by using a method called ‘Oversampling and Decimation’. This method requires a noisy signal at input, although the charger itself generates some noise, the noise level might be not enough. For this reason cheali-charger has a buildin artificial ADC noise generator, you can enable it in settings (adc noise: yes).

The artificial noise is added by pseudo-randomly charging two capacitors when no measurement is performed:

Downside of this solution is that the noise is positive and it depends on the input voltage.

note: noise is only addend to the BAT+ and BAT- terminals, if you are using the balance port it will not affect battery voltage measurements (balance port voltage measurement is more accurate, we used it whenever possible).

enabling artificial noise

To enable the artificial noise set: options->settings->adc noise: to yes. You can check if it's working by connecting BAT+ and BAT- terminals to GND and going into options->calibrate->expert DANGER!, you should see:

• Vplus: 0.015V
• Vminus: 0.015V

If one of the voltage is 0.000V it is very likely that your charger don't have the required capacitors:

If possible, find the missing elements and put a 100nF capacitor into it, although only noise on BAT+ is necessary.

differences between adc noise: yes/no

adc noise disabled, notice the 29mV "stairs":

adc noise enabled:

nuvoton M0517 cpu

The measurement is sufficiently accurate, we don't need any artificial noise.