Alt-BEAM Archive

Message #07526



To: beam@sgiblab.sgi.com
From: "Jim Cook" beamboter@hotmail.com
Date: Wed, 10 Nov 1999 16:41:58 PST
Subject: [alt-beam] evandude@yahoo.com


>okay, I made a photopopper from my own tutorial... it
>seems to work with the right motor, but the left motor
>has that buzzing noise to it. I went to chiu's
>tutorial, and looked at the troubleshooting part, and
>it led me to believe that the 3906 was the problem...
>I will redo the solder joints tomorrow(too much
>soldering tonight aaagggh!) but in the meantime, does
>anyone want to please check the connections on my
>tutorial to make sure it is correct? thanks.
>


I went to your page and couldn't see the graphic of the conections...the
were scrathed or lined kinda funny...

Sincerely,
Jim Cook
beamboter@hotmail.com
http://www.geocities.com/Area51/Nebula/9874




______________________________________________________



7527 Wed, 10 Nov 1999 16:43:46 -0800 [alt-beam] Re: Pots in the head "'beam@sgiblab.sgi.com'" Wilf Rigter As a follow up:

While R1 value must be large compared to the effective photobridge
resistance, the RC time constant of the Nv/Nu stage (R2/C2) should be
slightly longer than the R1/C1/photobridge time constant. So R2/C2 can be
any reasonable values such as a 250K trimpot and 0.22uf . Aside from the
requirement for a high value R1, it is the ratio of the R1/C1 and R2/C2 time
constants that is important.

regards

Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411

> -----Original Message-----
> From: Wilf Rigter [SMTP:Wilf.Rigter@powertech.bc.ca]
> Sent: Wednesday, November 10, 1999 1:14 PM
> To: 'beam@sgiblab.sgi.com'
> Subject: RE: Pots in the head
>
> Hi Victor,
>
> Good point about naming conventions. When I say pot or potentiometer, I
> mean
> a single or 10 turn screwdriver adjustable "miniature trimpot" (which are
> always linear) unless otherwise specified. The 5M single turn units I use
> are made by Phillips but I have no part number, they were cheap less than
> $1
> each. The 5M - 10 turn trim pots Bourns Series 3296 from Digikey cost $4
> and are easier to fine tune. Alternately use 3.3M fixed resistor in
> series
> with a 1M pot for R1 and R2 with the fixed resistor for R1 at the output
> of
> inverter A. Lowering the R total value of R is not recommended since it
> should be high compared to the resistance of the photobridge. You can use
> a
> variety of C values 0.1 - 0.01uf is ok
>
> regards
>
>
> Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
> tel: (604)590-7493
> fax: (604)590-3411
>
> > -----Original Message-----
> > From: Victor Snesarev [SMTP:snesarev@ecel.ufl.edu]
> > Sent: Wednesday, November 10, 1999 10:58 AM
> > To: BEAM List
> > Subject: Pots in the head
> >
> > Hi,
> >
> > After reading Wilf's wonderful tutorial, I decided to build a PS Head.
> > Once I started looking for components, though, I found that either a
> > 5MEG pot is not easy to come by, or I am looking at all the wrong places
> > (DigiKey, All Electronics, ....)
> >
> > First is a question of naming things. I call a potentiometer a variable
> > resistor with a longish nob that can easily be turned with fingers, and
> > a trim potentiometer a boxy-looking device (plastic on the
> > outside--that's all i've seen) with a tiny screw. Trim pots seem to be
> > used in photopopers for example. Am I naming these devices by their
> > correct names -- names that a supplier of these parts would use? Oh, and
> > then there are tapers, and I think they look more like potentiometers,
> > but I am not sure.
> >
> > DigiKey doesn't have any pots over 2MEG. However, All Electronics has a
> > 5MEG linear taper (PC mount pot with 3/16" diameter, half-moon nylon
> > shaft. Non-threaded bushing.) PC mount, and 3/16" diameter make me
> > believe that it is one of those small deals that would fit nicely on a
> > head. Am I wrong?
> >
> > And the final issue. Since the frequency of the of the HI/LO OSC, and of
> > Nv/Nu stage is controlled by the resistance of the pots (R1 & R2) and
> > cap. values (C1 & C2), is it feasible to increase the C's, and decrease
> > the R's to get the same RC constant and hence frequency? With
> > approximate values from the tutorial
> >
> > RC = 2.5MOhms * 0.01uF = 250KOhms * 0.1uF.
> >
> > I.e. replace the pots by 500K pots and the caps by 0.1uF caps.
> >
> > Thanks in advance for any info.
> >
> > Victor
> >
> >



7528 Wed, 10 Nov 1999 20:56:57 -0400 [alt-beam] touch lamps "alt-beam@egroups.com" michael.hirtle@ns.sympatico.ca (Michael Hirtle) How do touch lamps work, it seems they only work when u touch them with
your skin

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