Need to shutdown at night - CDS cell control
GICU812
Posts: 289
I have a time controlled camera project that runs on a AA and I really need to conserve power wherever possible. It doesnt take pictures in the dark, so I need a way to shutdown the controller at night. Ive got some CDS cells and transistors and a whole box of componets, I just dont know how to assemble them.
I dont know which way would be best, but·I could either pull the RESET line on the MC low when dark, or just to cut power to the controller. The controller is running off 3.3V
IIRC, a CDS cell has lower resistance in light so Im guessing maybe just a PNP transistor inline with the power line, and the CDS cell grounding the base? I just dont know how to work that in with the required support componets, it doesnt need a lot of adjustment, just off at or near dusk.
So can anyone help me here? It would be great if you could answer any questions I had once we have a basic design, so I can learn why it works, for future projects.
·
I dont know which way would be best, but·I could either pull the RESET line on the MC low when dark, or just to cut power to the controller. The controller is running off 3.3V
IIRC, a CDS cell has lower resistance in light so Im guessing maybe just a PNP transistor inline with the power line, and the CDS cell grounding the base? I just dont know how to work that in with the required support componets, it doesnt need a lot of adjustment, just off at or near dusk.
So can anyone help me here? It would be great if you could answer any questions I had once we have a basic design, so I can learn why it works, for future projects.
·
Comments
Post Edited (GICU812) : 7/16/2008 11:52:34 PM GMT
CDS transitor light dark schematic
[noparse]:)[/noparse])
- Howard
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Buzz Whirr Click Repeat
However smart Google may be,·it doesn't seem to answer this correctly·(yet):
How do I make a million bucks drinking beer, sitting·in front of the Tube?
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Buzz Whirr Click Repeat
Post Edited (CounterRotatingProps) : 7/17/2008 1:08:40 AM GMT
How do you make a million bucks drinking beer and sitting in front of the tube? You don't, Budweiser makes the millions.
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It's sunny and warm here. It is always sunny and warm here.... (unless a typhoon blows through).
Tropically, G. Herzog [noparse][[/noparse] 黃鶴 ] in Taiwan
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Im not that bright and i can prove it.
http://www.parallax.com/Portals/0/Downloads/docs/books/edu/Wamv2_2.pdf
Chapter #7: Measuring Light · Page 189
Light Detector Test Parts
(1) Photoresistor
(1) Resistor – 220 Ω (red-red-brown)
(1) Capacitor – 0.01 μF
(1) Capacitor – 0.1 μF
' What's a Microcontroller - TestPhotoresistor.bs2
' Read photoresistor in RC-time circuit using RCTIME command.
' {$STAMP BS2}
' {$PBASIC 2.5}
time VAR Word
DO
HIGH 2
PAUSE 100
RCTIME 2, 1, time
DEBUG HOME, "time = ", DEC5 time
LOOP
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··Thanks for any·
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Sam
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
I think i'm onto something, I just havent had time to prototype it. My main problem so far is the circuits Ive found dont really pop on or off, there is a transistion period where the transistor is partially on, Im afraid this will damage the tiny
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Time·─ Space·─ Gravity·─ Darkness·─ Death
I just tried one of the circuits I found on google, I thought it looked wrong, moronic was more like it, I told myself, theres no way this can work. Smoked a transistor, I should have listened to myself, haha.
Very Nice·
For IC 1 Voltage Comparator will any one do·or what heve you used before
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··Thanks for any·
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Sam
Post Edited (sam_sam_sam) : 7/20/2008 2:58:31 AM GMT
You could configure any op-amp as a comparator, practically, but comparator IC's like the LM339·yield better "rail-to-rail" results.
If you need to add hysteresis to your circuit, here is a simple modification to PJ Allen's design.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.