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Topic:
Cheap Light Controller Technical Question
This thread has 4 replies. Displaying all posts.
Post 1 made on Monday January 9, 2017 at 23:56
Ernie Gilman
Yes, That Ernie!
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This is actually unrelated to A/V stuff.

I've got a few strings of white LEDs that plug into the wall and have a small control box with a single pushbutton that switches the lights into different patterns of lighting. Inside the box there's an IC and four transistors about the size of 2N3914s. I worked out previously that each transistor controls one fourth of the lights.

I want to just plug this thing in and have constant light, so I want to stop the switching from one pattern to another.

A few years ago I worked out the schematic for these things but I've lost it. In that one I removed the IC and I'm pretty sure I just tied the bases of the transistors high after that. But I'm looking for something even simpler.

It occurs to me that, since SOME LEDs are ALWAYS on, though not always the same ones, maybe if I just tie all the transistor bases together without any other circuit changes, they'll all just stay on. The possible flaw with this is that if all are ever off at the same time, then the combined setup will still go dark momentarily every once in a while. I don't see that in the patterns, but things move quickly in some of the patterns.

Now, this is a silly inconsequential thing, but it's also a way to learn things and it's fun. Be critical if you want.

Does anybody have any idea whether there'd be a problem tying the bases together to get what I'm looking for?
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 2 made on Tuesday January 10, 2017 at 08:02
buzz
Super Member
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Can the power supply support all strings ON simultaneously? Also, can the strings be ON 100% without dissipation issues?
OP | Post 3 made on Tuesday January 10, 2017 at 11:26
Ernie Gilman
Yes, That Ernie!
Joined:
Posts:
December 2001
30,104
One of the various combinations of lighting is ALL ON all the time, so, yes. Right now it's been on this way for two hours, and it was on this way last night for about six hours.

I don't understand the difference between your two questions. It seems to me that if there were dissipation issues, the power supply would not be able to support all strings being on simultaneously, and vice versa. You might be asking "if you try to have them ON all the time, does the power supply smoke or do the LEDs smoke?" That question would be secondary to "Can they all be on at the same time?"
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 4 made on Tuesday January 10, 2017 at 18:33
buzz
Super Member
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May 2003
4,366
It is possible that the LED's are pulsed. While it may appear that that all are ON at the same time, they could actually operate in four phases. (each phase being approximately 25% ON time) Tying the gates together will create a single phase. Then there is the issue of "pull-up" or "pull-down" for the parallel gate drive scheme. Do you have enough or too much gate drive current?
OP | Post 5 made on Wednesday January 11, 2017 at 14:33
Ernie Gilman
Yes, That Ernie!
Joined:
Posts:
December 2001
30,104
buzz,
no, I don't have that info.

Of equal import is this: how fancy will be a five dollar string of LEDs? Right now they are all "on," whatever that is, and they are all pulsing. (Stare at something, then move your head slightly but rapidly left and right, letting your eyes go with your head. You will see lights on constantly or they will appear to be on and off as they cross your field of vision.)

Oddly my cell phone doesn't see any pulsing, but the controller is too small for a filter cap, so the LEDs are definitely NOT seeing DC!

About pull-ups and pull-downs, good call. I'd not worry about them, since if this doesn't work I'll be throwing away a product I don't want the way it is. Thanks for thinking of these details!
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw


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