Alt-BEAM Archive

Message #10288



To: beam@sgiblab.sgi.com
From: "Sathe Dilip" sathe_dilip@bah.com
Date: Wed, 16 Feb 2000 13:12:13 -0500
Subject: [alt-beam] Re: pdiode ptransistor?


It's not that simple. A photo transistor, when its base is properly
biased, can give you some current (induced by photons/light in this
case) amplification. A photo diode will just give you the increase in
leakage current when exposed to light. Getting the first stage of
amplification right at the source is important when you are dealing with
low noise requirements in a circuit. In BEAM environment where usually
we are using the sensor to give us a presence/absence of light type of
indication, this may not matter that much. But say you want to build a
light beam communicator, and you will see the need for a low noise input
stage.

Dilip
--------------------------------------

Dane Gardner wrote:
>
> Actually a transistor is two diodes back to back.

SNIP
----------------------------------------------------------------------
The early bird may get the worm, but the second mouse gets the cheese.
----------------------------------------------------------------------



10289 Wed, 16 Feb 2000 13:29:32 -0500 [alt-beam] Re: Solar cell Q beam@sgiblab.sgi.com "Sathe Dilip" I do not have the ratings of a 3733 handy but let me generalize the
answer. If you do not exceed the manufacturer's voltage rating, you can
not kill a capacitor by feeding it with a high current source. In fact,
I have read that by derating a capacitor for voltage, every 10% derating
doubles the operating life of a capacitor (ofcourse you are out of luck
if the electrolyte dries up before you get 10 times the life).

Generally the manufacturers play it safe & design the components to
withstand higher stresses than the rating. I think Dave Smith (spelled
Hrynkiw :-) has done some experimentation to see how much you can
stretch this limit for the Panasonic gold caps. You may find this info
on the Solarbotics site somewhere.

Dilip
--------------------------------------

Thomas Pilgaard wrote:
>
> Can you actually kill a cap say by hooking up a 3733 solarcell to a 1F cap
> with a max. of 2.5 volts?
>
> Thankyou
>
> Thomas
>
> > -----Original Message-----
> > From: owner-beam@sgiblab.sgi.com
> > [mailto:owner-beam@sgiblab.sgi.com]On Behalf Of Sathe Dilip
> > Sent: Wednesday, February 16, 2000 5:03 PM
> > To: beam@sgiblab.sgi.com
> > Subject: Re: Solar cell Q
> >
> >
> > Then the solar cell prevails. The capacitor in this case (depending on
> > value) can help smooth out some output voltage variations that would
> > have happened in changing light conditions.
> >
> > One example would be a bot (say a solar roller) crossing a shadow area
> > between two well lit zones. The capacitor can provide the power
> > required to coast through the shadow area.
> >
> > Dilip
> > -------------------------
> >
> > Steven Dang wrote:
> > >
> > > But what happens when the solar cell is able to provide more than enough
> > > current for the circuit.
> > >
> > > > > > The capacitor we connect in parallel with the solar cell
> > acts like a
> > > > > > current storage tank. You save enough current to last
> > you for a small
> > > > > > burst of motor (run) power. The level of current stored
> > in the tank is
> > > > > > indicated by the voltage on the capacitor. How much
> > current you can
> > > > > > store is decided by the size/value/capacity of the capacitor.
> > > > > >
> > SNIP
> > ----------------------------------------------------------------------
> > The early bird may get the worm, but the second mouse gets the cheese.
> > ----------------------------------------------------------------------
> >

--
----------------------------------------------------------------------
The early bird may get the worm, but the second mouse gets the cheese.
----------------------------------------------------------------------



10290 Wed, 16 Feb 2000 12:06:47 -0700 [alt-beam] Re: Solar cell Q beam@sgiblab.sgi.com Dave Hrynkiw At 10:51 AM 2/16/00 , Thomas Pilgaard wrote:
>Can you actually kill a cap say by hooking up a 3733 solarcell to a 1F cap
>with a max. of 2.5 volts?

You will shorten it's life span, and it'll charge up to only about 4V. It
will rapidly decline back to ~2.8V after the source voltage is removed. I
regularly "stretch" the 2.5V gold caps to 3V with the slow charge the
solarcell provides.

Regards,
Dave
---------------------------------------------------------------
"Um, no - that's H,R,Y,N,K,I,W. No, not K,I,U,U, K,I,_W_. Yes,
that's right. Yes, I know it looks like "HOCKYRINK." Yup, only
2 vowels. Pronounciation? _SMITH_".
http://www.solarbotics.com



10291 Wed, 16 Feb 2000 12:20:16 -0700 [alt-beam] Re: Solar cell Q beam@sgiblab.sgi.com "John A. deVries II" At 09:03 AM 2/16/00 , Sathe Dilip wrote:
>Then the solar cell prevails. The capacitor in this case (depending on
>value) can help smooth out some output voltage variations that would
>have happened in changing light conditions.

I'd like to point out an item on one of Lee Golden's pages:

http://www.geocities.com/leemon1/Bots/beambots.html

Look for Mr. Pock, his version of an experiment I did that shows exactly
the effect you are describing. As he says:

>Mr. Pock takes a few minutes to begin blinking under my 40W desk lamp, but
>it continues to blink for over 15 minutes after the lamp is turned off.


Zoz

p.s. More on the original "Proof Of Concept Mark I (pockmark)" can be found
on that site that I'm perpetually pushing, that is:

http://www.serve.com/heretics

following the path

BEAM Heretics: Other BEAM People: Zozzles T. Freep: Proof Of Concept
- Mark I.

Lee's version is hugely more aesthetically pleasing and the blinking LED is
a nice touch.


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