Author Topic: Battery Voltage Monitoring  (Read 25139 times)

TomWS

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Re: Battery Voltage Monitoring
« Reply #45 on: March 01, 2018, 05:59:34 PM »
I suspect it's not just the settling time, you'd need to slow the ADC clock right down so that the sample and hold window is large enough to allow the high impedance source to charge the S&H capacitor. Just allowing a longer settling time on the pin isn't enough.

Mark.
Wanna bet?   ;)

The MUX will charge the SH Cap as soon as the MUX is changed if there is no conversion underway.  The charge in this case is a function of the source impedance and the setup time of the MUX.  Once the conversion is underway, the source is actually disconnected from the S&H cap one clock period after SC.

Another time related factor, however, is the effect of any filter capacitor on AREF if the reference voltage is changed.  If you're reading VCC, however, then this is the default reference and the AREF voltage should be stable.

Tom

perky

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Re: Battery Voltage Monitoring
« Reply #46 on: March 02, 2018, 07:20:43 AM »
I've been labouring under the misapprehension that there was a 2 clock sample window! It appears I may have got confused with continuous sampling mode in the past. You're completely right, thanks Tom for pointing it out ;)

Mark.

TomWS

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Re: Battery Voltage Monitoring
« Reply #47 on: March 02, 2018, 08:01:55 AM »
You're completely right, thanks Tom for pointing it out ;)
Dang!  I was hoping to make my retirement fortune off this bet!
Good working with you, Mark!
Tom