You might find this useful also.
http://www.pbpgroup.com/modules/wfse...p?articleid=25
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You might find this useful also.
http://www.pbpgroup.com/modules/wfse...p?articleid=25
Dave
Always wear safety glasses while programming.
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Thanks. I don't have any trouble working out the divisor so that it wont go over 5v for my input range. It's the impedance that I was worried about (but still want to minimise wasted current).Originally Posted by mackrackit
It's a shame that DT's calculator there doesn't have the impedance in the result. I have yet to find confirmation elsewhere that the input impedance is the parallel impedance of the 2 resistors. It seems a little counter-intuitive to me. If anything, I would have thought that it would be the series impedance.
"I think fish is nice, but then I think that rain is wet, so who am I to judge?" - Douglas Adams
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Consider BrianT answer confirmed
This may help, near the end....
http://www.kpsec.freeuk.com/imped.htm
Dave
Always wear safety glasses while programming.
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Thanks BrianT and mackrackit.
It still seems counter-intuitive to me, but it means that I can have accurate battery readings with less wasted current, so I'm happy.
Last edited by Kamikaze47; - 11th August 2010 at 16:10.
"I think fish is nice, but then I think that rain is wet, so who am I to judge?" - Douglas Adams
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An easy way to understand it without going into thevenin equivalent circuits.
Consider the plus side and the 0 (ground) side of the power source as low impedance sources. In an ideal power source the + side and 0 side will each be zero ohms impedance and as such the PIC sees both the high side resistor and low side resistor going to to zero ohm sources making the value of the resistors parallel.
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Nice explanation!Consider the plus side and the 0 (ground) side of the power source as low impedance sources. In an ideal power source the + side and 0 side will each be zero ohms impedance and as such the PIC sees both the high side resistor and low side resistor going to to zero ohm sources making the value of the resistors parallel.
Dave
Always wear safety glasses while programming.
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...or put a largish capacitor accross the pic pin and use the ESR of the cap as your source impedance!
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