Looking for help with circuit revision

[[email protected]]

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

--------------------------------------------------

So, your final circuit comes out looking like this:


+5>---+-------------+
| |
[68k] [LDR] +---[1M]--+
| | | |
| +----+---|+\ |
| | | >--+---->OUT
[100K]<--[10K]---|--------|-/ |
| | LM324 [1.5k]
| [3.9k] |A
| | [HLMP4700]
| | |
GND>--+-------------+--------------+---->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.

-------------------------------------------

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

 

[DJ Delorie]

I now need to invert the output

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

 

[John Fields]

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

--------------------------------------------------

So, your final circuit comes out looking like this:


+5>---+-------------+
| |
[68k] [LDR] +---[1M]--+
| | | |
| +----+---|+\ |
| | | >--+---->OUT
[100K]<--[10K]---|--------|-/ |
| | LM324 [1.5k]
| [3.9k] |A
| | [HLMP4700]
| | |
GND>--+-------------+--------------+---->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.

-------------------------------------------

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?

---

This may work:

.. +5>---+-------------+
.. | |
.. [68k] [3k9] +---[1M]--+
.. | | | |
.. | +----+---|+\ |
.. | | | >--+---->OUT
.. [100K]<--[10K]---|--------|-/ |
.. | | LM324 [1.5k]
.. | [LDR] |A
.. | | [HLMP4700]
.. | | |
..GND>---+-------------+--------------+---->GND

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

 

[John Fields]

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

 

[Rich Grise]

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

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

+5>---+-------------+
| |
[68k] [LDR] +---[1M]--+
| | | |
[100K]<--[10K]---|----+---|+\ |
| | | >--+---->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

 

[[email protected]]

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.