Alt-BEAM Archive

Message #04354



To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Tue, 08 Jun 1999 19:14:44 -0400
Subject: [alt-beam] SE questions not found in the FAQ.


I have a few questions on the D1 and PM1 solar engine schematics found
at:

http://www.beam-online.com/Robots/Circuits/circuits.html

This is the second version of the 'D1' schematic I've seen. Something
looks wrong here.

First, if I adjust the 150k pot to its minimum resistance value, the cap
will never charge.
And if the gate of the 2N7000 is really directly connected to the
negative side of the solar
cell, what is this pot supposed to be adjusting anyway? Simulated
capacitor leakage?

Maybe the gate of the 2N7000 is supposed to go to the wiper of the pot?

Then there is that 4001 diode. Should it really be between the cap and
the solar cell?
Your going to loose a full .7 volts here alone.

Shouldn't that really be a 1N5817, or at least a 1N4148, and place it
between the source
of the 2N7000 and the negative connection between the cap and solar
cell?

Using a high-side PNP switch is a lot more efficient, and much more
minimal than the D1 engine
and rare 2N7000 fetlington.

As drawn, I can beat this circuit in 3 parts, all from Radio Shack.

There must be an error here somewhere, or I'm missing something big.
Does anyone have a detailed theory of operation for this circuit?

Now, about that PM1 drawing...

What is the reason for having the .47 uf cap and 47K resistor across the
load being controlled
by the PM1?

Clearly (as drawn) we need to get current through the 4001 diode to
charge the .47 cap on the
1381's input. (so this wont trip at the 1381's preset voltage?)

So why not place the 47 k resistor between the positive supply and the
input of the 1381, with
the .47 uf cap to ground.

Could we then eliminate the 1N4001 completely, or is this needed to
discharge the .47 uf cap?
(there is nothing like this needed to discharge the .22 caps in a
photopopper!)

If so, lets really slash and burn, and simply connect the input of the
1381 to the positive side
of the main capacitor, and be done with it! (we have eliminated 4 parts
from the circuit.)

Does anyone understand why the published circuits are shown this way?



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