All an inductor is (basically) is a coil of wire; an electromagnet:
They can be wrapped around nothing (air core), or around ferrous materials ("iron" core - although typically an actual piece of iron or steel is -not- used, unless a really high value is desired or needed; these cores are generally composed of a ceramic core that has ferrous particles in it and of course they also vary in size, shape, and composition, which will also have to be chosen). Which core (and shape/composition) you use (plus the type and gauge of wire) will of course change the inductor's properties.
Winding one the size you need will take some guesswork and some experimentation (I don't have any experience with this - and I am certain it shows - this is all based on my reading). To help with that guesswork, I would look into finding some tables describing common sizes for inductors, how many turns, what kind of cores, etc; you might have to look into older articles and such from the heyday of radio and analog electronics for some of the information. In the meantime, while you do research, you can also experiment.
Get a meter that can read and output inductor values, wind some simple inductors and take readings. Note the number of turns used, the diameter of the coil, how far the individual coils are spaced, what kind of core was used, etc - in a notebook as you take readings. Vary (as much as possible) on one of the variables at a time and take individual readings to see how that changes them (hint: the Henry is a unit of magnetism, so anything that makes a strong electromagnet will increase the number of Henries).
While I can't tell you what inductor to use exactly, the above should give you an idea of how to make one that potentially could be the value you need. Inductors are one of the few (perhaps the only) electronic parts that can still be hand assembled by a hobbyist - they should only be purchased if you need particular exact values, small size, standardized components, or another such need where a hand-wound one can't be used reliably.
given my swiss cheese electronics background, i'd be worried that i'd get lost quickly if i tried winding my own - i wouldn't know if i'd be way over or under my needed spec. between core type (where to get that ceramic stuff??) wire type (all i've got is stripped CAT5) and how many times to wind it...
but all this is lazy talk. i'll have to give it a shot if there's no better alternative than flailing in the dark
but all this is lazy talk. i'll have to give it a shot if there's no better alternative than flailing in the dark
You can buy inductors; you could try pulling some yourself from old electronics (old power supplies and similar). Whatever you do, you should get a meter that can read inductance values.
But winding and playing with them yourself is easy; get the meter, take a wire from the cat5, straighten it as much as you can (or get a piece of straight wire - cat5, being twisted pair - can be difficult to straighten), and wrap a few turns around a pencil. Measure it with your meter. Change the spacing of the coils. Measure it again. Add some coils. Measure. Stick a small nail in. Measure. Stick a large nail in. Measure again.
Inductors are electromagnets. I was playing with electromagnets when I was six years old (maybe I am just weird, or an old-fogey, but as a child I used to play with all sorts of electric and electronic crap I scavenged from around the house and neighborhood). They are simple. Inductors are simple. As I said before, they are the one electronic component you can still homebrew from "nothing" (capacitors, especially large ones, would be another - resistors too, to an extent).
Give it a shot; you have nothing to lose (well, a few dollars for the meter, of course, if you don't already have one), and a lot to gain (knowledge)...
thanks, cr0sh, for your help and for your degree of detail. i'm at work right now (computer labs teacher) and while the kids are working this would be a perfect time to give this a try...if only i'd brought my multimeter to school. rats.
can anyone offer some suggestion as to why the 2nd set of inductors i bought aren't working?
nym
ps i'm thrilled to have gotten this non-inverting amplifier working. i feel like successes are so few and far between that i nearly jump for joy when something finally works!
can anyone offer some suggestion as to why the 2nd set of inductors i bought aren't working?
Well that inductor has a maximum DC current rating of 50mA (from the data sheet) and I assume your circuit takes more than that. What happens with inductors is that the magnetic core saturates if you put too much current down it and you don't get the right inductance.
ok. i got the inductor working. i had accidentally removed the decoupling capacitors on my IR. the noise is gone on my circuit.
however, the inductor does the same thing the resistor did just before the power on the IR sensor: it reduces the usable range of the sensor by upping the "off" signal.
in other words, with no inductor or resistor, i get a usable range of 0 through 800 or so. however, i get that undesirable noise on the arduino's other inputs
WITH the inductor or resistor, i get an (un)usable range of 450 - 800 or so.
does anyone have a comment as to what may be happening here? is this standard for inductors, did i misinterpret something?
that inductor has a maximum DC current rating of 50mA
??What inductor? Did some messages get dropped or removed or something?
An inductor with a maximum rated current of 50mA is likely to have a relatively high DC resistance, and if used "near" 50mA may cause a significant voltage drop. That's not what you want if you're trying to remove noise from the power supply for a sensitive analog component (though it could be acceptable for any number of other circuits.) Keep an eye on that DC resistance specification, and find something with a LOW value there...
Did some messages get dropped or removed or something?
Yes it looks like it. It was a link to a component suppliers page and the first thing I noticed is the maximum current. I can't check now but I also think the resistance was in the region of 80R.
@nym
The point of using an inductor in place of a resistor is that you don't get the volts drop. As westfw said the DC resistance of this inductor is too high. The dropping off in range is almost certainly due to a reduction in voltage caused by the resistor. Look for something with under 10R DC resistance.
checking shows that the max dc current is indeed 26.4Ohm...equal to the resistor that i was using previously. no wonder it shrank the usable range of the sensor by the same amount...
wish i'd been more thorough before buying these, but i guess this is all just part of obtaining a usable bank of parts...
thanks fellas.
Inductance: 15 mH
Tolerance: 10 %
Maximum DC Current: 0.4 Amp
Maximum DC Resistance: 4.912 Ohms
Self Resonant Frequency: 0.2 MHz
Q Minimum: 61
Operating Temperature Range: - 40 C to + 85 C
Termination Style: Radial
Dimensions: 25.1 mm Dia. x 18.5 mm L
Series: 1400
Test Frequency: 10 KHz
i'm starting to wonder if the sharp IR sensor is just futile to use in applications which require other analog ins. using it without conditioning makes all the other inputs jittery because it draws unpredictable amounts of power, and conditioning it like i've been trying to just makes it only usable over a span of like 2 inches.
Try a bigger capacitor on the component side of the choke, something like 100uF.
If it is a decoupling problem (which I think it is) it can be cured with the right component values.
