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biketool is offline biketool
2013-06-02 , 08:10
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#81
For the high power settings a ultra short pulsing will be brighter than 100% on duty cycle. As a white LED heats up its brightness drops and our eyes cant tell that it is a pulse over something like 30-60x a sec.
 

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malfunctioning is offline malfunctioning
2013-06-02 , 08:15
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#82
Using the indicator LED in torch mode is surprisingly useful in very dark environments, even if the light pattern is not ideal because of the indicator LED being further recessed behind the main LED lenses (creating two bright circles on the left and right).

I assume the 17.5mA is the maximum load the indicator LED will accept, or is there a way to push it beyond that safely?
 

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Copernicus is offline Copernicus
2013-06-02 , 08:21
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#83
Originally Posted by malfunctioning View Post
I assume the 17.5mA is the maximum load the indicator LED will accept, or is there a way to push it beyond that safely?
Yes, 17.5 mA is, in fact, the absolute upper limit available for the indicator LED using the ADP1653 control chip. I don't know if the LED itself could take more, but there's no way to feed it any more...
 

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pichlo is offline pichlo
2013-06-02 , 08:25
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#84
20 mA tends to be the normal continuous current for low-power LEDs. If our controller chip says 17.5 mA, then 17.5 mA it is.
 

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malfunctioning is offline malfunctioning
2013-06-02 , 08:29
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#85
Originally Posted by biketool View Post
For the high power settings a ultra short pulsing will be brighter than 100% on duty cycle. As a white LED heats up its brightness drops and our eyes cant tell that it is a pulse over something like 30-60x a sec.
I was attempting to give this a try. The lowest flash duration I can get is 29ms, and the lowest strobe pause I can get is 50ms. These values are too high (it only results in a little over 12 cycles a second, so the flashing is clearly visible, although I do see how getting closer to the values you mention would fool the eye (traditional cinema is 24fps).

The strobe pause lower limit seems to be hardcoded (the field resets to it if you enter anything lower), but the flash duration is not (the LED just doesn't light up with anything lower than 29ms).
 

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Copernicus is offline Copernicus
2013-06-02 , 08:43
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#86
Originally Posted by malfunctioning View Post
The strobe pause lower limit seems to be hardcoded (the field resets to it if you enter anything lower), but the flash duration is not (the LED just doesn't light up with anything lower than 29ms).
The minimum strobe pause of 50 msec is due to me -- I was nervous about allowing strobe calls with no pause at all between them. But yeah, the minimum 29 ms flash duration does appear to be a hardware limitation, even though V4L2 allows shorter durations.
 

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qwazix is offline qwazix
2013-06-02 , 08:49
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#87
This might be useful.
http://fcam.garage.maemo.org/apiDocs...1_1_flash.html


weirdly,

The flash on the N900 must fire for a multiple of 54.6 ms plus one millisecond (go figure).
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fw190 is offline fw190
2013-06-02 , 08:55
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#88
All the torch apps have a nice option to start from status menu. Would it be possible to have such thing here or will this mess up the app?
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malfunctioning is offline malfunctioning
2013-06-02 , 09:02
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#89
Originally Posted by pichlo View Post
Just a bit of theory. Flasing LEDs can take several times their nominal continuous current for a long time, even permanently, provided that two conditions are met.
1) The maximum pulse current is not exceeded;
2) The duty cycle is set such that the average current over a longer period of time does not exceed the maximum continuous current.

I don't know what the maximum pulse current for our LED is but it usually tends to be 10 to 20 times the maximum continuous current. If the chip allows 320 mA, then I would stick with it. The other bit is the duty cycle. At 1:1 duty cycle, you are right not to allow to stress the LED for too long. Setting it to 1:5 might allow you to breathe a bit more easily.
If I'm understanding this correctly, running a 1:2 duty cycle (for example 50ms flash duration and 50ms strobe pause) at 320mA would be equivalent to an average current of 160mA (3.2 times the maximum continuous current). So probably not good to run that cycle for a long time, correct?
 

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pichlo is offline pichlo
2013-06-02 , 09:20
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#90
Originally Posted by malfunctioning View Post
If I'm understanding this correctly, running a 1:2 duty cycle (for example 50ms flash duration and 50ms strobe pause) at 320mA would be equivalent to an average current of 160mA (3.2 times the maximum continuous current). So probably not good to run that cycle for a long time, correct?
Spot on!

(Except that I like to think of 50 ms on, 50 ms off as a 1:1 duty cycle. 1:2 would be 50 ms on, 100 ms off. To avoid confusion, it is better to use percentage terms as per this Wikipedia article.)
Last edited by pichlo; 2013-06-02 at 09:39.
 

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flashlight, lanterne, morse code, nokia n900, strobe light, torch

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