Alt-BEAM Archive
Message #02121
To: JVernonM@aol.com
From: Bob Shannon bshannon@tiac.net
Date: Thu, 08 Apr 1999 20:19:39 -0700
Subject: [alt-beam] Re: D1-Diagnosis Please
JVernonM@aol.com wrote:
>
> Hello all,
> I currently have a D1 solar engine on my breadboard. I have the outputs
> connected to a FLED. It seems to work well with one exception. Occasionally,
> the circuit will not switch from charging the cap to lighting the FLED when I
> move it into darkness. If I "bump" the circuit by holding it close to a
> halogen light source and then place it in the dark, it begins working. It
> seems to do this only after sitting and charging for a while. Once bumped it
> will work normally as I move it from dark to light. What could be the
> problem? I have a 47k resistor in place of the 150k variable resistor. Could
> the resistance be to low? Is it possibly the FLED itself? Any advice is
> greatly appreciated.
> Jim
I see you using the updated D1 engine. There are two versions of the D1
engine
I've seen on the web. I've not personally experimented with the later
version
with the 150K resistor.
I have worked on the original circuit, and concluded its designed not to
work
very well (or at all).
If you check the specifications for the 2n7000, you will see that it
takes
more voltage to switch than is dropped by a single diode junction.
Personally I use a NPN phototransistor to starve a PNP high-side switch
of its base current, holding the PNP off while there is light. It works
very well, and has
a fairly low light-leakage current.
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