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Find highest value of 4 inputs without microcontroller?
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german77:

--- Quote from: fsr on November 17, 2018, 03:32:10 am ---The optocoupler idea is quite clever!
But without a uC, how will you read the result, and how will you actually select the analog line, etc?
From a cost perspective there could be some cheap, low pin-count uCs with several ADCs out there.
But it all depends on how will you use the result and the signals.

--- End quote ---
The optocoupler may sound clever but it's actually horrible considering that you need 1.2V or something like that, of difference to know for sure which one is the highest. I'm sure he does use a uC to read the result but he doesn't want to waste ADC pins or resources to do this task.
Wolfgang:

--- Quote from: german77 on November 17, 2018, 02:45:53 am ---I will go with comparators any time. But I like doing things the hard way  ;D. This idea is similar to the optocoupler idea but with transistors. From the emulation I can expect a minimum of 0.15V difference to say for sure which one is the maximum.

--- End quote ---

You could make this idea more accurate by using transistor array ICs, one for NPN and one for PNP. Within an array, Vbe does not differ much.
Kleinstein:
For the transistor circuit it would help a lot if the emitter side resistor to the negative supply would be replaced with a constant current source of some type. This would make the level where the circuit starts to see a difference more independent of the absolute voltage level.

Adjusting the current to the right level (around 1 mA for the shown circuit) can also reduce the turn over range, from a case where no output might be marked to the case where 2 about equal outputs would be marked.
DC1MC:
You can draw some inspiration from the patent here:
https://patents.google.com/patent/US6191623B1/en


 DC1MC
spec:
The requirement sounds quite simple at first, but there is more to it than meets the eye

The four LED circuit is so clever. :)

It does have a lack of precision though and there is a danger of exceeding the LED reverse voltage. Of course, that depends on the voltage of the input signals.

Attached is a precision version of the four LED circuit. In addition to the the highest voltage LED illuminating while the others are off, the three off outputs will be at logic 0. But the highest output will be at whatever the highest voltage input is.

I haven't worked out a simple way to produce a solid logic 1  :-\
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