Looking for help with circuit revision

Aug 17, 2007 5 Replies
K

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



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D

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

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J

This may work: . +5>---+-------------+ . | | . [68k] [3k9] +---[1M]--+ . | | | | . | +----+---|+\\ | . | | | >--+---->OUT . [100K]---+-------------+--------------+---->GND But just to be sure, what was the original application?
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J

Not really, since then the hysteresis would be negative feedback instead of positive.
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R

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

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K

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.

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