Electronics > Electronics

Trouble Understanding Level Shifting

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johnwarfin:

--- Quote from: jwatte on September 23, 2013, 07:33:26 PM ---Make sure it's low impedance enough to be able to drive the ADC inputs!
...

An alternative would be to re-buffer with an opamp set for partial gain.

--- End quote ---

unfortunately an op amp, aside from costing 10x more, would require negative supply to function properly. imo simple divider is best. ratio but not actual values would be the concern. a cap not only solves the impedance issue there but added benefit of reducing noise.

Sylvestre:

--- Quote ---the only real confusion if any was use of "bbb". normally this refers to avr Bare Bones Board.

--- End quote ---
I must be on the Beaglebone forums too much, I've gotten accustomed to that abbreviation. 


--- Quote --- imo simple divider is best. ratio but not actual values would be the concern. a cap not only solves the impedance issue there but added benefit of reducing noise.
--- End quote ---

Ok sounds good.  Thanks.

jwatte:

--- Quote from: johnwarfin on September 24, 2013, 12:52:16 PM ---An alternative would be to re-buffer with an opamp set for partial gain.

--- End quote ---

unfortunately an op amp, aside from costing 10x more, would require negative supply to function properly. imo simple divider is best. ratio but not actual values would be the concern. a cap not only solves the impedance issue there but added benefit of reducing noise.
[/quote]

Right. If you can live with the RC filter (or even desire it) then the resistor divider is best.

A rail/rail opamp doesn't need a negative supply, and can run at much higher frequencies with lower current draw. Whether the $0.90 instead of the $0.09 matters is of course very application specific.

johnwarfin:
after checking prices i see my 10x figure was inaccurate. the actual cost difference between that oa and a couple resistors is closer to 100:1. as far as single supply r-r op amps they fail miserably near ground and vcc. i stand by my comment that cheapo divider is the best/only reasonable solution. ymmv (but not likely)

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