Alt-BEAM Archive

Message #09289



To: "'beam@sgiblab.sgi.com'" beam@sgiblab.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Mon, 17 Jan 2000 12:47:54 -0800
Subject: [alt-beam] Re: D1


Hi Steve,

Sorry for the delayed reply. Don't get too frustrated: technical =
problems
make life interesting and are an opportunity to learn.=20

Sure use 1N4148 or any other diode.

The charge pump cap is 47uF. Other values will work too but the =
duration of
the flash is proportional to the size and smaller caps appear less =
bright
while larger caps may waste energy compared to the small increase in
apparent brightness.=20

Your LED comes on and stays on: I am not surprised! Don't forget the =
reason
for designing this circuit was the high forward voltage of the blue LED =
and
the whole question of driving LEDs from a supply voltage below the LED =
turn
on voltage.

If you read my email carefully, you'll will see that the basic circuit =
is
designed for a +V of 1.5-2.0V. Above that voltage the LED with the =
series
diode start to conduct and will stop the +V voltage on the 1F cap from
rising any higher. I also suggested that if you use a higher voltage =
solar
cell and capacitor then put 2 red LEDs in series to increase the =
forward
voltage of the LEDs/diode load.=20

For this circuit, the maximum fully charged solar capacitor voltage =
should
be less than the turn-on voltage for the LEDs or else you would not =
need
this circuit in the first place. For one red LED with a series diode =
that
voltage is between 2.1 and 2.5V. With 2 red LEDs in series and a diode =
the
turn on voltage is between 3.7 and 4.5V =20

I mentioned designing several versions of the circuit and while this =
one is
the simplest design some, I have another version that doesn't have the =
LED
coming on when charging the cap above the LED/diode voltage. That =
circuit
is a little more efficient and has quasi constant brightness current
limiting for the LED while it only requires one more component.=20

I will post it next.

regards

wilf

> -----Original Message-----
> From: Bumper314@aol.com [SMTP:Bumper314@aol.com]
> Sent: Sunday, January 16, 2000 4:05 PM
> To: beam@sgiblab.sgi.com
> Subject: Re: D1
>=20
> even more questions...can you use 1n4148 diodes? is that cap on the =
output
> of=20
> the inverter 47=B5f or .47=B5f? I made this thing and the LED just =
stays on
> all=20
> the time once there is enough voltage in the cap to turn it on...I am
> really=20
> getting pissed here. You have made it as simple as possible, and im =
trying
> to=20
> get back into BEAM with all this simpe crap but i cant do jack. =
DAMN!!!!
>=20
> Steve



9290 Mon, 17 Jan 2000 15:04:44 -0500 [alt-beam] Re: sensors "Richard Caudle" http://members.home.net/cybug/Chloro/chloro~1.htm

Also, you can find a photopopper that uses the Chloroplast on my site:

www.geocities.com/frankendaddy/theother.html

There's also a link on the HPV Project Page of my site.

Richard


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