Alt-BEAM Archive

Message #05022



To: beam@sgiblab.sgi.com
From: James Taylor edgar_the_hate_bug1@yahoo.com
Date: Sun, 4 Jul 1999 17:55:51 -0700 (PDT)
Subject: [alt-beam] Re: Something funny with the 1382 voltage triggers?


Current draw on those little Transistors. Thats my
guess, could switch to heavy duty type SMT trans.
Maby 2222's, and 2906? Thats what I noticed with my
SMT Solar engine.



--- Bob Shannon wrote:
> I've just been playing with a SMT SE, and noticed
> something odd I've never
> encountered
> before.
>
> These surface mount solar engines are built on
> 'SurfBoards', small commercial
> SMT prototyping boards that resemble a Basic Stamp
> SIPs, but are blank.
>
> I build several SE's with these boards, using 1382-J
> voltage triggers and real
> McCoy SMT 3094's and 3906's. My capacitor is 6,600
> uf, and I'm using a 3733
> solar cell.
>
> The problem is lock-up under full sun. The problem
> does not happen with indoor
> lighting
> unless the photovore is held abut 5 cm from a full
> spectrum desklamp.
>
> I changed the resistors from 2.2K to 1.8K, with no
> effect.
>
> Trouble shooting with a scope gave me a supprise or
> two. First, the SE is not
> oscillating.
> Secondly, the lock up condition happens at low cap
> voltage, rather than just
> before the trigger
> point.
>
> The main cap voltage rises to the trigger point, a
> motor fires and the voltage
> drops down, then never rises again. The cap does
> not charge until the light
> level drops, a lot.
>
> I have never seen this failure mode with 1381-J's,
> even using identical motors,
> capacitors, and
> solar cell. (in fact, I'm duplicating a photovore I
> gave away as a gift, only
> using my SMT engine boards rather than the free
> formed SE's used in the
> original)
>
> Has anyone notices a difference when using SMT
> components rather than thru-hole
> parts?
>
> I'll search the FAQ again, but I dont recall ever
> reading about a fails to
> charge in bright light problem before, or not one
> where the circuit works well
> in modest lighting. I can only presume that one of
> the SE's is not shutting
> down as it should.
>
> I hate the thought that I might need to add a
> resistor between the solar cell
> and main cap if thats whats going on here. Is there
> another solution? Or is
> it possible that this is an internal resistance
> (ESR) problem with my drive
> capacitors?
>
> This particular photovore has larger caps than many,
> and higher powered, but
> more efficient
> motors (as compared to pager motors) beacues it
> needs to carry some extra
> cargo. This extra cargo casts a shadow over the
> main drive 3733 solar cell, so
> I was going to add a small booster cell (2224) on
> the tail, facing the rear.
> This will provide additional current when the 'bot
> is facing away from the
> light, and compenstate for the shadow on the main
> cell.
>
> With this high light level lockup problem, I worry
> that this additional cell
> will only make things worse. (I'll add them in
> parallel, with 1N5817
> schottkey's to prevent back feed)
>
> My next question is this, is there a way to control
> this effect? Can I get a
> photopopper to stop
> once its found a really bright spot to feed? (so
> the cargo systems may operate
> till the light level drops off and its time to go
> hunting again)
>
> Last question, what is the limit of a photopoppers
> ability to climb over
> obstacles?
>
> How many can roll over a dime, or quarter, or the
> thicker US nickel? How many
> can roll
> over a 1/8th watt resistor and other bench clutter?
> Ever seen a photovore turn
> a 2N3906 into
> road-kill on the bench?
>
> This has a lot to do with wheel diameter and torque.
>
> Pager motors are efficient, but have little useful
> torque. There are many
> motors that are just
> as efficient, or more efficient, but they need a bit
> more power than a pager
> motor to produce far more torque (walkman motors are
> a good example of this).
>
> I find that these slightly higher powered, but more
> efficient motors will drive
> wheels up to
> about a centimeter in diameter without gear
> reduction. The result is a
> photovore that covers
> more ground per minute, and a greater range of
> terrain as well.
>
> (this explains the 6,600 uf cap and -J type triggers
> I'm using with salvaged
> motors from laptop
> CD-ROM drives)
>
>

===
Everything I say can mean one of two things...If something I say makes you mad....I meant it the other way.

James Taylor
URL: http://fly.to/springmeadows
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