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Looking for help with circuit revision

The following circuit was designed for me by John...

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So, your final circuit comes out looking like this:

+5>---+-------------+ | | [68k] [LDR] +---[1M]--+ | | | | | +----+---|+\\ | | | | >--+---->OUT [100K]--+-------------+--------------+---->GND

I've added a little hysteresis to keep the output from chattering as the + input goes through the trigger point, and also used a high-efficiency LED to allow more output current from the opamp into whatever OUT is feeding.

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I now need to invert the output - is this something I can do with the existing components, or will I have to add an addtional invertor to the output?

Any help greatly appreciated.

Dave

Reply to
kasterborus
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Can't you just swap the + and - inputs?

Reply to
DJ Delorie 

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This may work:

. +5>---+-------------+
.       |             |
.     [68k]         [3k9]  +---[1M]--+
.       |             |    |         |
.       |             +----+---|+\\   |
.       |             |        |  >--+---->OUT
.    [100K]---+-------------+--------------+---->GND

But just to be sure, what was the original application?
Reply to
John Fields 

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Not really, since then the hysteresis would be negative feedback
instead of positive.
Reply to
John Fields

How about if you just swap them before the hysteresis feedback?:

+5>---+-------------+ | | [68k] [LDR] +---[1M]--+ | | | | [100K]--+---->OUT | +--------|-/ | | | LM324 [1.5k] | [3.9k] |A | | [HLMP4700] | | | GND>--+-------------+--------------+---->GND

Or, you could have turned the 324 upside down, as long as the 1M goes with it.

Or am I missing something?

Thanks, Rich

Reply to
Rich Grise

Thanks for the responses!

The original application was a musical instrument triggered by interrupting laser beams. I'll give these designs a try.

I've also been given a couple of GP2D120 reflection sensors - I know that the output of these is in the range of 0.4-2.45v. Can I adapt the above components to work with these instead?

Thanks in advance - I wish I knew how to do this stuff myself.

Reply to
kasterborus

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