Alt-BEAM Archive
Message #00786
To: Justin jaf60@student.canterbury.ac.nz
From: Steven Bolt sbolt@xs4all.nl
Date: Mon, 22 Feb 1999 19:22:49 +0100 (CET)
Subject: [alt-beam] Re: reversing photovore circuit - comments? (was It works, but I don't know how... new diagram)
On Mon, 22 Feb 1999, Justin wrote:
> > 1) Remove the led - collector BC548 directly on enable input 245.
> > 2) Connect resistor of for instance 100K from enable to Vcc (+ solar
> > panel).
> >
> > Now assuming that your storage cap has a sufficiently low internal
> > resistance to handle your motors, I would expect the circuit to do
> > what you expect :)
>
> I did that last night when trying to figure it out, and yes, it now
> works as expected. I used a much larger resistor though, and going on
> the principle that I didn't really want my precious power going through
> a resistor once the SE tripped, found an 8M resistor worked fine.
> (overkill? :)
You're using that transistor as an inverter only, no amplification
required. It's perhaps best to set it up for about 0.5uA of base
and collector current; 1M base resistor, 1M pull-up on collector.
It doesn't make much sense to have an 8M pull-up and then allow
90ua to leak away as base current, through that 47K base resistor.
Photovores can run on quite a bit less than 90uA *total* current :)
> http://www.geocities.com/soho/lofts/1121/beam/bivore.gif
Had a look...
> It seems a fairly obvious design, so I'm sure someone has done this sort
> of thing before, and I'm wondering how efficient this one is - is there
> a better way to do this? Comments?
> My own (crude) tests indicate it draws about 0.2mA, which seems to be a
> fair bit.
...And that's rather high. Your choice of chippery does not look
ideal. However, there are much worse Solar Engines in common use!
Best,
Steve
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# sbolt@xs4all.nl # Steven Bolt # popular science monthly KIJK #
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