EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: Phillipthegreat on February 03, 2018, 05:30:18 am
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Hello, all
I've got a simple circuit I'm putting in a project wherein a hot ac-line photocell controls a usb powered strip of lights. It works great, in that it responds to light. However, when the room is bright/the photocell blocks power, every 5ish seconds, it lets power through for a fraction of a second and the lights blink on and then off. I need this to not happen because it's absolutely obnoxious. I figure that there's some small, cheap module out there that can make this stop, maybe by delaying the power from the cell by a second so that the cell has to allow power through for at least a second to actually power the lights on. Is this something common for photocells?
Thanks a bunch for any help!
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AC line? USB?
If it's the light sensor letting leakage current through, try putting a DC load on it, like an incandescent nightlight, or a resistor.
Tim
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Can you post what exactly you ave?
Brand and type of the photocell and USB lightstrip?
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Parts: the resistor is a philmore 'photo-electric switch', 25W max load, 125ac. The lights are this:https://www.amazon.com/gp/product/B01LY0M4D3/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1 (https://www.amazon.com/gp/product/B01LY0M4D3/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1). The converter is a cheap "xtreme" 2.1 amp wall adapter.
I ordered an on-delay timer module that I figure will fix this, but its gonna be a while in shipping.
It already has a DC load on it with the lights, doesn't it? Or do I need a stronger load on it? I could also put it on a multimeter to see how much power it's letting through.
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does it click when it turns on/off?
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Yeah, try putting, like, an incandescent night light in parallel with the power supply AC input.
Tim
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The photocell is not allowing "blips" of power through. It is allowing a steady stream of minute power to flow across, most likely due to capacitive coupling. This slowly builds up charge in a capacitor in the LED light power supply, and when enough charge has accumulated, the LED regulator switches on for a moment and then the charge is gone. Then, the cycle repeats.
A small load on the AC mains input to the wall adapter will stop this. Loading the output of the wall adapter might not, as the wall adapter may be the thing accumulating charge and then pulsing on.
Jon
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p.s. Don’t let the photocell ‘see’ any light from the LED strip, or it may become a low frequency oscillator!