Electronics Forum / Basics / November 2006

   I am an absolute beginner at electronics.
I need a DC motor (probably a 1.5 to 9V hobby DC motor from radio shack).
I need to be able to vary its rotational speed.
By chance, I happen to have a 555 IC.

Can someone explain to me how to apply Kirchoff's Law to this circuit?
http://www.progressivetel.com/~radney4/kl.jpg
Thanks!
Lee

If a Bosch-type relay is rated say "20/30 amps," which set of contacts
is the "20" -- energized or not-energized?
Ken C

Will a phono preamp work for boosting the line-out signal from a
computer sound card to that of 'speaker level' for running a set of
small non-amplified stereo speakers ?  The speakers do sound reasonably
well at the line-out level, their volume is just somewhat low, even at

I posted a message a while back on recommendations for an oscilloscope. This
would be my first one primarily used for experimentation and basic circuit
analysis. Someone recommended a Tektronix, but I can't find the post
anywhere. Which model is good to start with?

i have to convert 50V analog at 100KHz to 50V digital at 100KHz, so i
need help, like how do i proceed what is in my mind is to step down the
voltage 50V to the one that can be fed to an A to D converter IC and
then may be i can then use a DC-DC amplifier to bring the voltage to

So I've got two 20 ft lengths of rope light:
Specs: AC 120V, 60Hz, 0.5A
And I'd like to use one or both via battery power. Can anyone offer any
help on how I'd go about doing this?

how to make a crystal /ceramic oscilator for a specicfied frequency in
kHz range ?
Is it posssible to make one on myself, or find someone to make it ?
What is a minimum order quantity for a crystal/c eramic resonator for a

Thanks for response to my previous request.
Followed each reply and still don't know how to make kHz tuning fork
(as an electronic component).
Queried Wikipedia for tuning fork.

I'm an artist/designer and just a tiny bit familiar with electronics
and I'm conducting some research for an art project about the
electrical properties of oilpaint. A lot of pigments used in
traditional (oil)paint colours are metallic oxides. For example

I'm interested in interfacing to a board that sports a ldo regulator that
fix the supply to 3.3V. The regulator is REG102NA-3.3 Actually i don't need
such a regulator beacuse the only supply i have is already 3.3V. I was
wondering if i can feed the regulator with 3.3V (Vin = Vout in ...

What I would like to do is to put a clip on a 16-64 pin chip and see
what is happening on each pin. Using a computer or dedicated Hardware
and see what the voltages are, what the grounds are, the VCC, See the
digital signal with the frequency.  I know a Logic Analyzer can track

Re: A/D converters - what is the difference, if any, between
sample & hold, vs. track & hold?
I hate getting hung up on jargon...
--

I am looking to buy a  DC Power Supply. I am not sure of getting a
digital or analog display. And also one output or two output.
Is there a specific use for one of the above or is it simply a decision
of personnel  taste..

Please point me toward any applicable FAQs or other groups if I am
breaking protocol or in the wrong place, thanks.  :)
That said, I am trying to find some information on building a very
simple circuit that combines a momentary contact switch and my PC's