Low power state of charge measurement of a battery (used to be Hello friends)

[Anctinget]

Hello friends,

Is there any superlow powered components or technique i can use to detect instantaneous charge state of energy reservoir (supercepacitor) and send feedback to microcontroller without adc's (to save power)? I have previously used a low powered comparator but it only measures either higher or lower than a threshold. I need to compare multiple threshold levels.

Thanks

Sincerely,

 

[Harald Kapp]

without adc's (to save power)

A bunch of comparators will probably ask for more power than an ADC. Although there are low power comparators which you can use. Depending on the number of thresholds you need this technique will become cumbersome quickly.
Many microcontrollers come with built-in ADCs and these can be disabled (aka put to low power or sleep mode) while not being used. The total power dissipation can then be easily controlled by adjusting the sample rate.
For checking a battery, measuring once every few minutes or even tens of minutes may be sufficient, making the power dissipation of the ADC almost negligible compared to the power dissipation of the controller.

Btw. 1: measuring the battery voltage is only a crude proxy for the state of charge. See e.g. here for more detail.

Btw. 2: I modified the title of your post - "Hello friends" doesn't say anything about your question and may not draw a lot of attention.

 

[danadak]

What is the necessary sampling rate for the measurement. the frequency you want to the
measurement ? And the accuracy and resolution of the measurement you desire ?

 

[Anctinget]

Thanks for reply.

 

[crutschow]

You can buffer the voltage with a low-power CMOS op amp (e.g. TLV915x) configured as a follower which will draw essentially no current from the capacitor (just the low bias current of 10pA for the referenced op amp).
The op amp output voltage can then be monitored by a low-power type micro with an A/D converter to determine the state of the capacitor charge.