a question about electronics for mr wizard

http://van.hep.uiuc.edu/van/qa/section/Everything_Else/Gizmos_and_Gadgets/20011120155811.htm

i'm not sure what type of motor... i'm assuming electric... if so, generally, the more voltage, the faster... so a variable resistor can be handy... you could use a pcm servo to digitally control the arm of a variable resistor (like the knob on your standard dimmer switch) type of thing...

again, i'm not remotely sure what you're doing... you may not need the servo at all if you just wanna hook a dimmer switch up to your motor... a digital interface may not be what you're interested in.
m.

basically i'm putting a fan motor in a turntable and then trying to make a pedal controlled turntable.

i have a record cutter and can make lockgrooves

you see where this is going... :D

I'm going to make the arm lockable and try to make some way of variably forcing the platter to be off center...

man, i wish i could put electronics brain power to good use. i think i've forgotten more than i know now tho.

use it or lose it.
m.

fourier transform ? that's the mathematical operation that turns a function of time into a function of frequency.... one f(x) into F(s)... or whatever goofy nomenclature you get bent on.

again, something i have forgotten more about than remember well... i think you can use a fourier t to do frequency based filtering and stuff... write one spectral analyzer. etc.
m.

except maybe

Potentiometer

http://www.kpsec.freeuk.com/symbols/vres3.gif
Potentiometer Symbol

Variable resistors used as potentiometers have all three terminals connected.
This arrangement is normally used to vary voltage, for example to set the switching point of a circuit with a sensor, or control the volume (loudness) in an amplifier circuit. If the terminals at the ends of the track are connected across the power supply then the wiper terminal will provide a voltage which can be varied from zero up to the maximum of the supply.

your audio signal is the function of time... like the amplitude over time... and that usually gets you a different wave form for a specific time that you can plug in a frequency and get a value... that shows you how much amplitude is rep'ed by that frequency... just like the spectral analyzer shows. lot's of his or lot's of lows or whatever...

[fuck... brain, where are you?] i know from there you can also take that new F(s) and remove terms and then go back to the t domain with that signal and totally remove parts of the signal... you can do that with specialized amplification junk too but but but...

i need to crack a book. [or book a CRACK]

potentiometer = dimmer switch essentially. and that should work with AC just the same as DC i would think. it's just a resistor right?

m.

also because I suck at EE now.

http://www.eatel.net/~amptech/elecdisc/potentio.htm

could this help?
m.

that other terminal is the terminal that has the output voltage on it... so it's connects to the + terminal input of your motor... and you just connect the the - terminal of the motor to the common ground i'm assuming.

does that make sense?

xpost mflic...

but the thyristors can be used to make ac control circuitry, although how to do so is beyond me because I never got that far.

but hey, i'm more of a DC electronics guy. digital stuff is mostly all DC and that's what my schooling was more in.
m.

we used to do fourier like all THEE FUCKIN time... and now i'm like, huh? curse this metal body! == one goldenrod.
m.

I just found this... I am going to read it sometime.

I don't know enough about how AC motors work to reason it out, though

right?

aren't there two pin Pots? why does a pot need 3 pins?

like... imagine it's four pins... two in, two out...but one of each side is just wired to the same node on the circuit. they share the common ground.

using that in AC land should produce a similar effect... we did AC voltages in our circuits and amps classes... you use a signal gen... and watch the output in an o-scope. i wish you had a singal gen and o-scope to watch it work. like, isn't the negative terminal ground? if you've got a power source that's +/- 15 V at 60Hz... your positive terminal... the red power terminal goes from +15V to -15V right? i would've thought a POT would just divide that voltage depending on where the slider or knob is... +/- 3V...

but as wayne said, the AC engine might need a different driving force. in a way... same idea as a pot, but the circuit has to be a little more complex...

http://www.electricmotors.machinedesign.com/guiEdits/Content/bdeee2/bdeee2_1-4.aspx

this has some stuff that might be of use... you don't know what kind of electric motor it is, do you?

"With a universal ac motor, speed control is simple, since electric motor speed is sensitive to both voltage and flux changes. With a rheostat or adjustable autotransformer, ac motor speed can be readily varied from top speed to zero."

"Using an Automotive Rheostat for Fan Control"
http://www.overclockers.com.au/techstuff/a_rheostat/

m.

?

but yeah, in AC land, capacitors and inductors get have extra components beyond simple resistors... a motor should be made of inductors... so...

http://www.allaboutcircuits.com/vol_2/chpt_3/2.html

? granted, this is like second semester circuits class shit... i'm not sure if these pages of theory will help more than just cause brain overload.

chapters even further forward:

http://www.allaboutcircuits.com/vol_2/chpt_10/4.html

??

dude, those are some whompin' voltage controllers... "nice dials!"
m.

More than likely, if the motor came from a fan you've probably got a universal AC motor. It either has the currents on the armature and field windings reversed for a constant voltage, or basically has a rectifier in it that just converts the AC to DC. Then the speed control is done with a rheostat I believe, as mentioned above.

But even if you get that worked out you might have problems crafting a usable pedal out of any components you can put together. My suggestion would be to go to a Salvation Army or something and buy an old sewing machine with a speed control pedal. You could just use the guts to do exactly what you want and experiment with gear ratios to get the speed right.

any sparks still on noise?

i have a basic question re electrolytic capacitors.

how important is the physical size of a capacitor? for example, if i was to replace a capacitor with a new one of identical voltage and number of farads, but it was a few milimetres smaller, would this negatively effect it's performance?

i just asked my EE friend on aim. he's at lunch. i'll answer in an hour

ah thanks man

http://wiki.answers.com/Q/Does_the_physical_size_of_a_capacitor_make_a_difference_if_the_values_are_correct

short answer: no
long answer: size doesn't matter but is a byproduct of the dielectric, voltage rating, and capacitance value
beyond voltage and capacitance, the type of dielectric has the largest bearing on performance

forgot to tell him it was electrolytic. this is his answer when i told him it was.

oh then it doesn't matter as long as the capacitance is correct and the voltage is the same or higher
those caps are shit and used in non crit applications usually