goofy

Using LEDs as photosensors is fair game - some solar powered night lights do that these days. But the whole premise is bonkers. I am amazed to see that it is published with a current date... shortage of articles?

I blame user error. A PIC micro on a 32kHz watch crystal at 3v will draw about 10uA running continuously iff you remember to turn off the output pullup resistors and disable any other current hungry components when not in use. I have a LCD based design that runs with a 16F877 direct driving the LCD and takes about 12uA running continuously with a 32kHz Xtal clock reading inputs and maintaining the display.

Something tiny like a 6-pin 10F200 should draw 180uA on 2v @ 4MHz and

0.1uA in standby/sleep mode if used correctly.

Regards, Martin Brown

On a sunny day (Wed, 23 Dec 2009 20:54:13 -0800) it happened John Larkin wrote in :

I measure

60 mV from a clear red LED 10 mV from a clear green LED 21 mV from a clear blue LED in front of window with a little sunshine. Those are all high effciency recent LEDs. If indeed the LEDs are onl ysensitve to a specific spectrum band, then maybe Icould make a TV color adjuster with 3 LEDs Does anybody know this? Else I need to make a prism setup some day.

For that circuit I would use a PIC.

Brain dead--full moonlight is about 1 lux, so a LED at 10 m is going to be dimmer than 10 lux.

Cheers

Phil Hobbs

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Using LEDs as photosensors is OK except that there's no pulldown, and LEDs have really really low leakage currents even with moderate amounts of forward bias. U1B could be drawing significant quiescent current due to picoamps of board leakage.

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Dr Philip C D Hobbs
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email: hobbs at electrooptical dot net
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REALLY GOOFY!

If you ground one input of a NAND, what do you get? ... Output ALWAYS HIGH ;-) ...Jim Thompson

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I can't see how that's a latch, with one input of U1A locked to ground.

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John

You have a problem with using two gates for an inverter? You're sounding like Joerg, now. ;-)

I think someone just won a bet that it would get published...

Bwahahahahahaha! ...Jim Thompson

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I measure 1.4V from a GaAlAs red LED (illuminated by a CF lamp at close range), pretty much what one would expect.

Why so different? Hint: I used an Agilent 34401A voltmeter.

Best regards, Spehro Pefhany

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On a sunny day (Thu, 24 Dec 2009 13:57:36 -0500) it happened Spehro Pefhany wrote in :

Yea, I used the 5 Euro digital multimeter :-) But why do they use a LED to measure sunlight? Any LDR will do. It is indeed goofy.

Yep, and then someone walks by in his new Air Jordans, touches LED ...

*PHUT*

Oh wait, they shut the store here because of the crowd so that won't work (yet).

Whenever light would bias it in the middle it'll draw a substantial amount.

I am surprised the author hadn't heard about the MSP430.

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With no light, its an invalid state for an NAND latch like that.

Cheers

Seems like they meant to hang everything from +V or to use a NOR.

Tim

-- Deep Friar: a very philosophical monk. Website:

It's not in any way invalid. The output of the "latch" is always known (in fact, trivial).

I always disliked the word "invalid" for the state where both gates are "on". It's not invalid, though the result are be unknown if the inputs transition *simultaneously* from the so called "invalid" state to the memory state.

No, they likely meant to have a switch where the grounded input is. OTOH, that's not the only thing that's screwed up with this circuit.

And what function would a latch have here, even if it did work?

Electronics Design is sort of fading away, in more ways than one.

John

They get a lot of new Ideas for Design... from kids in India ;-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
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NO, it didn't explode. :)

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