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Find highest value of 4 inputs without microcontroller?
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SiliconWizard:
Yes, dividing resistors + probably buffering to get reasonable accuracy. That's 4 more opamps then. Not easy! :D
There's a few MCUs with 4 integrated opamps though (very few), you can have a look at Microchip for instance. Could then be reasonable.
spec:

--- Quote from: SiliconWizard on November 19, 2018, 07:10:54 pm ---Yes, dividing resistors + probably buffering to get reasonable accuracy. That's 4 more opamps then. Not easy! :D
There's a few MCUs with 4 integrated opamps though (very few), you can have a look at Microchip for instance. Could then be reasonable.

--- End quote ---
Can't you get MCUs with Hi Z analog inputs?
T3sl4co1l:
I wouldn't worry about buffering to MCU ADC inputs.  Well, as long as they're conventional; who knows what you get at that price point.

The firmware dev time will likely dominate well over the parts cost and layout time, until large production quantities.

Got a schematic for that firmware handy? :-DD

Tim
spec:

--- Quote from: T3sl4co1l on November 19, 2018, 07:14:47 pm ---I wouldn't worry about buffering to MCU ADC inputs.  Well, as long as they're conventional; who knows what you get at that price point.

The firmware dev time will likely dominate well over the parts cost and layout time, until large production quantities.

Got a schematic for that firmware handy? :-DD

Tim

--- End quote ---

I agree- just had a look at a couple of MCU datasheets.  :)
SiliconWizard:

--- Quote from: spec on November 19, 2018, 07:14:32 pm ---
--- Quote from: SiliconWizard on November 19, 2018, 07:10:54 pm ---Yes, dividing resistors + probably buffering to get reasonable accuracy. That's 4 more opamps then. Not easy! :D
There's a few MCUs with 4 integrated opamps though (very few), you can have a look at Microchip for instance. Could then be reasonable.

--- End quote ---
Can't you get MCUs with Hi Z analog inputs?

--- End quote ---

Most are not internally buffered, so the inputs directly get to the internal sample-and-hold block through switches.
The most common max output impedance for input sources recommended for most MCUs I've seen is around 10k. Of course the end accuracy will depend on the sampling time, so without any buffering you'll be severely limited in sampling rate, unless you can use low-value dividing resistors if your input signals can drive that. So it will all  depend on the characteristics of your input signals and how fast you want your 4-input comparator to be. Another factor will be that most MCUs (especially the cheaper ones) only have 1 sample-and-hold block, meaning that you can't sample all 4 inputs at the same time, again this will hinder the speed and accuracy of the comparator. For slow-changing input signals, that would be adequate. But all in all, the cost, accuracy, simplicity, operating range and speed of the opamp/diode based solution is not that easy to beat.
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