do I need capacitor to use adc??

[sosse]

From this (https://devzone.nordicsemi.com/b/blog/posts/measuring-lithium-battery-voltage-with-nrf51), there is capacitor connected to adc input pin. 

But is it necessary to have the capacitor? what is there is no cap connected to adc input pin? is it possible to measure voltage? 

Thank you. 

[Einar Thorsrud]

Hi,

You do not always need a capacitor. It depends on the circuit you are measuring. There is a current inflow to the ADC peripheral when it is measuring (charging an internal capacitor), and this will affect the voltage you are measuring. In the post you link to, this would result in a lower voltage over the resistor you are measuring, causing you to measure a too low voltage. A possible solution is to use a capacitor as suggested. The blog has a fairly good explanation of the reasoning behind this choice.

[sosse]

Thank you for answering. So which case I don't need a capacitor? Can you explain more detail example which it doesn't need a capacitor? 

[Einar Thorsrud]

It depend on your setup, really. The ADC in the nRF51 has an internal capacitor which is 10 pF or less. This has to be fully charged from the circuit you are sampling during the sampling time. So if you are sampling a circuit that has a very limited capability to deliver current you could either use a very long sampling time or an external capacitor as a buffer, so that this can be used to charge the internal capacitor (which is the case in this blog post).