J. Yazel
Guest
Sun Mar 05, 2006 6:01 pm
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
Guest
Mon Mar 06, 2006 1:25 am
"J. Yazel" <jyazel_at_ds.net> wrote in message
news:j56m025c5rpibto0jk2t9vvlmqvr2nhe03_at_4ax.com...
Quote:
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
Guest
Mon Mar 06, 2006 4:05 am
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.
On Sun, 05 Mar 2006 12:01:58 -0500, J. Yazel <jyazel_at_ds.net> wrote:
Quote:
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
Jasen Betts
Guest
Mon Mar 06, 2006 10:13 am
On 2006-03-05, J Yazel <jyazel_at_ds.net> wrote:
Quote:
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).
most photocells are not much faster than that
basically you want a resistor and the photocell in series across the supply
with the mid point connected to the schmidt input.
try different resistors until you get the switching point where you want it.
1/4 of the dark resistance of the photocell may be a good starting point.
Bye.
Jasen
