3 ms·

If you have the LED hooked up in parallel with the chip, then you can't really do any fancy indication things like blink the LED, change colour (voltage level)

by kyzyl 13y ago

If you have the LED hooked up in parallel with the chip, then you can't really do any fancy indication things like blink the LED, change colour (voltage level) etc. It's possible that the engineers wanted to maintain that flexibility. Second, if the LED fails to a short your camera won't get any power. That means an expensive component appears to be broken when it's only a very cheap component, and you have no way to knowing that w/o opening up and inspecting or replacing parts. In contrast, if an isolated LED fails, one can still verify that the camera works via software, and choose not to send it in for repair. Also, LEDs have a very small leakage current even in their off state. If somebody is hyperoptimizing power consumption they might choose to put the LED on a high impedence controller output rather than feeding off a power rail or similar. Finally, the desired led might work off a configurable controller output, but that might not be the same as the output driving the chip enable pin. So you could require extra circuitry to convert to a compatible voltage/current level. That's my guess.

esmi 13y ago
Also, brightness trim via some sort of PWM on a GPIO.
lake99 13y ago
> Second, if the LED fails to a short your camera won't get any power. One never puts an LED on the power line directly. That will certainly blow up most LEDs. Power rails are typically 5V or 3.3V. LED drop is about 1V (+/- 0.3, varies between part numbers). There is always a resistor in series with the LED, to drop the rest of the voltage, and limit the current. So, LED getting shorted is not a problem. This is the case even when we're driving LEDs from an o/p pin. Besides, Hobbyists often blow up LEDs because they're still learning. But how often have you seen these tiny LEDs fail in professionally designed products? I have never ever seen it happen. Degrade and lose brightness over the years? Sure. Fail? Never. > LEDs have a very small leakage current even in their off state. Are you talking about reverse bias? That makes no sense in this context. When you don't supply any power to it, there is nothing to leak. > the desired led might work off a configurable controller output That is what has led to this mess of surreptitious filming, in the first place. It's time they went back to the old ways.
- kyzyl 13y ago
  Sorry I didn't check back here for a couple days. > There is always a resistor in series with the LED Sure, almost always. But there are many different voltage level, forward drop, forward current combinations for a given application. There's no guarantee, even with a ballast resistor, that the a shorted LED won't result in an effective short to the power rail (not a real short, but drawing close to the power supply's current sourcing limit). A resistor with a shorted LED results in a useless current sink, in any case. > But how often have you seen these tiny LEDs fail...I have never ever seen it happen. What you've seen or not seen has very little bearing on the reality that parts fail. Period. Things should be designed in a cost effective way that minimizes the possibility/effects of failures. FWIW, I had a laptop recently that had a dead LED on the front panel :-/ > There is always a resistor in series with the LED I just meant that if your "power rail" is actually just a signal line (or whatever) for some other purpose, and the led is there to indicate activity, then even in "low" signal states where the LED isn't fully conducting yet there is a small leakage current.
deleted 13y ago
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by kyzyl 13y ago

esmi 13y ago

Also, brightness trim via some sort of PWM on a GPIO.

lake99 13y ago

> Second, if the LED fails to a short your camera won't get any power. One never puts an LED on the power line directly. That will certainly blow up most LEDs. Power rails are typically 5V or 3.3V. LED drop is about 1V (+/- 0.3, varies between part numbers). There is always a resistor in series with the LED, to drop the rest of the voltage, and limit the current. So, LED getting shorted is not a problem. This is the case even when we're driving LEDs from an o/p pin. Besides, Hobbyists often blow up LEDs because they're still learning. But how often have you seen these tiny LEDs fail in professionally designed products? I have never ever seen it happen. Degrade and lose brightness over the years? Sure. Fail? Never. > LEDs have a very small leakage current even in their off state. Are you talking about reverse bias? That makes no sense in this context. When you don't supply any power to it, there is nothing to leak. > the desired led might work off a configurable controller output That is what has led to this mess of surreptitious filming, in the first place. It's time they went back to the old ways.

kyzyl 13y ago
Sorry I didn't check back here for a couple days. > There is always a resistor in series with the LED Sure, almost always. But there are many different voltage level, forward drop, forward current combinations for a given application. There's no guarantee, even with a ballast resistor, that the a shorted LED won't result in an effective short to the power rail (not a real short, but drawing close to the power supply's current sourcing limit). A resistor with a shorted LED results in a useless current sink, in any case. > But how often have you seen these tiny LEDs fail...I have never ever seen it happen. What you've seen or not seen has very little bearing on the reality that parts fail. Period. Things should be designed in a cost effective way that minimizes the possibility/effects of failures. FWIW, I had a laptop recently that had a dead LED on the front panel :-/ > There is always a resistor in series with the LED I just meant that if your "power rail" is actually just a signal line (or whatever) for some other purpose, and the led is there to indicate activity, then even in "low" signal states where the LED isn't fully conducting yet there is a small leakage current.

deleted 13y ago

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