Photocell circuit

[J. Yazel]

I would like to find a schematic for a photocell feeding a schmidt
trigger (CMOS). This will input the light from a not-very-bright panel
lamp. It is also very slow speed (once-a-half-second).

Any URL available?

Thanks for any help.

Jack

 

[Charles Schuler]

I would like to find a schematic for a photocell feeding a schmidt
trigger (CMOS). This will input the light from a not-very-bright panel
lamp. It is also very slow speed (once-a-half-second).

If it is a cadmium sulfide cell, the cell and a fixed resistor form a
voltage divider with perhaps 5 or 12 volts applied. Then, one just sets up
the trigger points (UTP and LTP) accordingly.

 

[Christopher]

Hello Jack,

I have a circuit and PDF PC board layout that could be modified into
what you need, especially triggering off a low level lamp output. This
will be using a photo-transistor which is more sensitive. Also using a
low powered TLC555 gives you a CMOS Schmidt Trigger.

http://www.oldtemecula.com/theremin/rs-opticaltheremin/rs-opticaltheremin.htm

If you leave everything as I designed, it would pulse/buzz a small
speaker every flash of the dim lamp.

Modifications for what you indicated:

Leave off C1 so it does not output a tone (oscillate), then adjust the
value lower of R2 a 1Meg resistor to give you the trip point you need.

Remove and "jump wire" C2 for a DC rail to rail voltage swing on the
output. Leave Pin 7 of the TLC555 disconnected or cut the copper foil.
Better yet use a IC socket and leave this IC pin folded upward.

Pin 7 is just above the "1" of the U1 label on the IC graphic.

Pin 1 has a black dot above it and the pins number counter clockwise.

I would like to find a schematic for a photocell feeding a schmidt
trigger (CMOS). This will input the light from a not-very-bright panel
lamp. It is also very slow speed (once-a-half-second).

Any URL available?

Thanks for any help.

* * *
Christopher

Temecula CA.USA
http://www.oldtemecula.com

 

[J. Yazel]

Hello Jack,
I have a circuit and PDF PC board layout that could be modified into
what you need, especially triggering off a low level lamp output. This
will be using a photo-transistor which is more sensitive. Also using a
low powered TLC555 gives you a CMOS Schmidt Trigger.

http://www.oldtemecula.com/theremin/rs-opticaltheremin/rs-opticaltheremin.htm

If you leave everything as I designed, it would pulse/buzz a small
speaker every flash of the dim lamp.
=======SNIP=========

Thanks very much. This looks very useful.

After a quick scan, I didn't see the photocell number. Do you have
it?

I'm going to drive an LED counter with it. I need to see when the
input lamp lights when I'm away and a rough count.

Thanks again.

Jack

 

[J. Yazel]

Photovoltaic or photoresistive?

=================

I'm not familiar with the terms but if photoresistive indicates
a cell that acts as a resistor, that's what I'm thinking that I need.

If there is a generator cell that will trigger a CMOS Schmidt,
then maybe I could use that. I don't think that I could adapt
it to the input lamp since I don't have any way to measure
the lamp intensity (not smart enough in optics).

Thanks.

And thanks to all other the other responders.

Jack

 

[J. Yazel]

After a quick scan, I didn't see the photocell number. Do you have
it?

I found it. Sorry.

Jack