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opinion request on 2 different comparator circuit designs

earckens

Member
Here are two designs for a circuit that detects ambient light and reacts according to its level compared to a reference lighting level.

Both designs incorporate both a comparator and a delay circuit (RC based).

The 4 channel version incorporates the delay circuit in the comparator input. The 2-channel version uses a comparator to compare lighting levels, and a separate comparator with a RC delay on its input.

Which of these designs carries your preference (and maybe: why?)?

Thanks!
Erik
 

Attachments

  • optical detector 4 channel v1.png
    optical detector 4 channel v1.png
    27 KB · Views: 39
  • optical detector 2 channel v3.png
    optical detector 2 channel v3.png
    30.1 KB · Views: 39

alec_t

Well-Known Member
Most Helpful Member
Why the diodes in series with C1 and C2? They will prevent C1 discharging and C2 charging.
The MOSFETS need pull-up resistors so that they can turn off.
The comparators have no hysteresis, so they will act erratically at the switching threshold.
 

earckens

Member
Hi Alec,
thank you for your reply. The first schematic will not work. The second works well for what it needs to do: detect light variation at low intervals (>1 second, up to minutes).

I made a new schematic, this time to compare the second circuit above with a design needing only one comparator.
I am in a bind however how to introduce a delay for the voltage on pin 9 (non-inverting) going up on the one-comparator design.

Downward voltage may be immediate; upward I would like to see an RC delay.

I have a gut feeling this will need an active component (mosfet)?
 

Attachments

  • optical detector 2 channel with delay.png
    633.8 KB · Views: 28

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