# project problems???

Discussion in 'The Projects Forum' started by Mathematics!, Jul 31, 2008.

1. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
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I am trying to create and verify a few devices and I cann't seem to get them to work at all.

First i wanted to make a simple microphone using the principle of induction.

So I have a magnet , some copper wire , a computer audio input connector , and a paper cup. I thought if you tape the magnet into the cup and poke a hole in the cup with the copper wires comeing into the cup. When you shout it moves the cup which vibrates the wire and should induce a current in the wire.

My problem is I am plugging this into an audio port of a computer.
And I cann't hear my voice at all. What voltage ranges does a typical sound card in a computer use? And what am I doing wrong?

Note I really don't care about the quality. Just want to see it work.
Don't really want to use anything more then the bare minimum for supplies in building the mic.

Second problem is I am trying to verify the law of induction by creating a magnet out of a screw. I wrap the wire around the screw about 10 times and plug the wire ends into a 9 volt battery. But I cann't see any noticable magnetic field induced. I tried picking up paper clips but no luck.

What could be the problem with this. How many times should I wrap the wire around the screw so I can see a noticable magnetic field.

Note I have seen a picture of somebody doing it with less then a nine volt battery on youtube.

Also what is the difference in using radio shacks insulated copper wire
As opposed to using radio shacks magnetic wire which is not insulated?

And when and why do you use insulated wire as opposed to non-insulated wire. Is it better to wrap insulated wire around the screw or not?

Thanks for any help.

2. ### Audioguru Expert

Dec 20, 2007
11,208
1,329
1) A microphone or a speaker has a coil of wire with many turns and a very small gap between the magnet and the coil.
You don't have a coil and you don't have a very small gap.

2) An electromagnet uses an iron core, not a steel core.

3) A little 9V battery provides low current. 10 turns of wire is like a dead short to it.
Your electromagnet will be 10 times stronger if it has 100 turns of wire and a battery with more current.

The turns of an electromagnet must be insulated.
Magnet wire has enamel paint as its insulation because it is strong and very thin.
The threads of a screw will cut the insulation. The core must be smooth.

3. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Well, that's "sort of" how speakers are made. Speakers have many turns of small-gauge magnet wire on a cylinder that's attached to the speaker cone. The cylinder is centered in a magnet. Having the coil move instead of the magnet keeps the weight (mass) of the moving parts low. If you examine a speaker, you'll notice that the perimeter of the cone either has a number of concentric ribs or a rounded foam thing. This allows the cone to move relatively freely, while keeping the cylinder centered in the magnet.

The tolerances are pretty close. It would be a challenge to build an efficient speaker from scratch.

Are you using the microphone input?
Just from what you've described, if you did get any output at all, it would be extremely low in volume.

If you do get any output, it will be of rather poor quality.

Are you using magnet wire or insulated hook-up wire?

Magnet wire has a very thin, nearly transparent coating of insulation on it. Years ago they used lacquer. Anyway, you need to remove the insulation by scraping or burning it.

Non-insulated wire will not work, as the screw will short out the coil.
Basically, the more turns you wrap around the screw, the stronger the magnetic field will be. You can wrap a bunch of turns on in a hurry if you use a piece of masking tape to hold the end of the wire to the screw, and chuck the screw in a variable-speed electric drill. Wear a glove on one hand, and keep just a light tension on the wire as you guide it. Run the drill at low speed.

I did a similar experiment many years ago using a very large 1 1/2v "doorbell" battery. The first time I tried it, I used non-insulated wire wrapped on a large nail. The nail did not become magnetized, but it got hot very quickly. I tried again using insulated wire, and it was strong enough to pick up other nails and paperclips.

The hook-up wire with colored insulation will have a much larger outer diameter than magnet wire, which will limit how many turns you can place in a small area. Magnet wire actually does have insulation on it. Buss wire does not have insulation on it.

Non-insulated wire won't work, as previously mentioned. The turns of the coils will be shorted out against each other and/or the screw.

4. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
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Quote: An electromagnet uses an iron core, not a steel core

I thought anything that is attracted by a permanate magnet is usually OK
to use. Anyway is iron much better then steel core?

As for what wire to use I have all different gauges.
But I will try the magnetic wire and wrap it a hundered or so times around.
I would think the equation for a solenoid would determine the strength of
the magnetic field B = (u N I)/h induced by a given current in the coil.
But what value in tesla's is a reasonable magnetic field to pick up small objects. Can you acheve this with a 1 volt , 5volt , 9 volt battery?

As for the microphone do I just take the magnetic wire and wrap it in coils and put it on top of the magnet. I mean the principles of induction say a change in magnetic field induces a current in a wire.
But if I am plugging this into my audio port on my computer the range has to corospond to that of the sound card. However I don't know what the voltages of a sound card operates at. I do know that we hear around the
20khz to 2000khz range. But I don't know how to position the magnet or if I should wrap the wire around the magnet and have two ends of wire sticking in the cup with the magnet taped out side the cup.

Any help would be great.
Just curious is it every a good thing to use non-insulated wire?
What is the physic's in non-insulated wire. Does it weaken the magnetic field ...etc etc?

5. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Yes, it would be better. However, for experimental purposes steel will work OK.

Like I said above, I made an electromagnet from a nail with perhaps 30 or 40 turns around it, and powered it with a 1.5V dry cell battery. It wasn't very powerful, but I could pick up small ferrous objects with it.

Ahh, that's from around 20Hz to 14kHz
That just won't work. Have a look at how speakers work:
http://electronics.howstuffworks.com/speaker.htm

Then have a look at microphone construction:
http://www.mediacollege.com/audio/microphones/how-microphones-work.html

6. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Ok I will try the 40 or more loops with a nail and a 9 volt battery.

As for the microphone I want to make a dynamic microphone from what I have. The only problem with their diagram is what is holding the coil from sliding back in forth. Like once I shout into it the coil will move down the magnet but what brings it back to it's starting position. Should I glue some
paper to the front of the coil and to the edges of the cup. So when I talk it vibrates the paper and oscilates the coil.

They did mention line level (typically 0.5 -2V )
I am assuming the audio sound card of a computer uses this voltage range for it's input on the mic port.

So if I can get it into this range I should hear my voice.
Or does my sound card amplify it from mic level to line level for me?
That would be even better and less to do.

Note I am not going for quality just proof of concept.

mic level, is typically measured in millivolts
Is their a typical range in millivolts to strive for?

7. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
That should work. Don't plan on the battery lasting very long though. Your magnet will act pretty much like a short circuit across the terminals. A 1.5v battery would work better and last longer.

You're going to need some kind of flexible mounting that will keep the coil centered over the magnet, but let it move easily back and fourth.

You haven't described your magnet, other than it's a magnet. A cylindrical magnet would be a good item to have for your experiment.[/QUOTE]

They did mention line level (typically 0.5 -2V )
I am assuming the audio sound card of a computer uses this voltage range for it's input on the mic port.[/QUOTE]
No, that's low-level audio. The mic input is very low level. I don't know exactly how much offhand.

Well, it's going to be difficult for me on this end to figure out what kind of output you might get from a homemade mic/speaker - since I have no clue as to the size or gauss of your magnet, what sizes of wire you have to work with, and what other kinds of raw materials you might have around.

8. ### Audioguru Expert

Dec 20, 2007
11,208
1,329
For deaf old geezers who have heard too many loud noises.
Young people can hear up to 20kHz and higher.

When I was young I heard ultrasonic motion alarms loudly. I heard 15,750Hz from TVs loudly. I heard high frequency distortion from sound systems that led me to learn about electronics to reduce the distortion.

9. ### Wendy Moderator

Mar 24, 2008
21,823
3,038
I haven't read all the posts, just thought I'd mention something my brother did when he was first learning, It was the classic nail with coils of wire around it to form an electromagnet. He then put it in inside a metal coffee can, where it worked quite well. Fidelity wasn't great, but what do you expect from a coffee can, nail, and wire.

10. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Yep, I used to hear pretty high frequencies myself, including the 15,750Hz from TV's. Used to drive me nuts.

Working on the flight line with dozens of F-4 Phantoms around took care of that problem.

11. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Well I have alot of different gauge wire 18 , 22 ,26, 30 to name a few I remember of the top of my head.

Why would a 1.5 volt battery be better then a 9 volt battery.
I thought the greater the voltage the greater the current.
Since current is proportional to voltage.
(i.e ohms law)

I only have radio shack batteries "alkaline enercell" 9 volt ones.

I tried wrapping 30 gauge wire around a soldering iron 50 times. Didn't work though.

As for the microphone I have Round Ceramic Magnets (5-Pack)
and one High-Energy Ceramic Magnet from radioshack.

The round 5 pack ones have a hole in the middle.
And the high energy ceramic is in the shape of a rectangular prism.

I have a digital multimeter if you would like me to try an get some measurements.

12. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Smaller gauge would be better for these projects.

Because the 9v batteries are rated for perhaps 150mAh, and even AA batteries are rated around 2500mAh nowadays.
That's true, but the short length of wire you'll be using will have very low resistance. This will cause the battery to waste most of it's power on it's internal resistance.

Not the ideal battery for this experiment. 1 1/2v "D" cells would last the longest.

That's because the tip of the soldering iron is made of copper. It won't work. Use something made from iron or steel, preferably rod-shaped.

One of the round magnets would be easier to use for a home-made "microphone".

You'll need to find or make a cardboard tube that's slightly bigger in diameter on the inside than the magnet. The tube will be the form for the coil windings. It must be straight, not tapered. You could make a tube from some typing paper and white glue. You'll need to use something as a form, and a rubber band or two to hold it in place while drying.

What were you thinking of measuring?

13. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Wait I found some AAA durecell 1.5 volt batteries.
I can use these if the are better then the 9 volt ones.
Note they only give the voltage not the current rating's.

So the internal resistance of the battery changes. I thought this internal resistance of a battery was always neglectable to the components of the circuit. I guess in the case of nothing but the battery and the copper wire
it would come into play.

Ohms law says r = v/i so r = 9 volts/150mAh
and we have AA being r = 1.5/2500mAh so then you are correct in saying that the internal resistance for the AA is smaller.

Anyway my batteries only gave the voltage. Shouldn't batteries always specify the current rating ? Because how else are you going to know the internal resistance without at least 2 of the 3 quantities? Is their like a standard for current ratings for batteries.

Also I would have thought that large volt batteries would have a current rating larger then a smaller voltage battery. Or then what is the point of buying a larger volt battery? Usually the smaller ones are cheaper anyway?

I will give it a try again with a AAA 1.5 volt battery and 50 wraps of 18 or 22 gauge wire around a nail or other iron or steel device (without copper ends). Thanks for that I did run a magnet over the end of my soldering iron an it didn't attract so I think it wouldn't have worked with anything.
Didn't realize the solder iron was a copper ended one.

As for the microphone I will give all this a try later but I want to get the induced magnetic working first.

I was talking about measuring the current down the wire of the microphone. To see if it is in the mic range.

14. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
That's a bit odd. Perhaps there wasn't enough space on the battery after they put their logo on. Look on the manufacturer's site for the mAh rating of the battery.

Normally, the resistance of the circuit is so much higher than the internal resistance of the battery, it doesn't come into play very much until the battery is pretty well used up. Then the internal resistance of the battery becomes so high that the output voltage is reduced.[/QUOTE]

Well, the internal construction of the batteries is quite different. D, C, AA, and AAA are all single cell batteries that produce 1.5v (rechargeables are 1.2v).
9-volt "transistor" batteries are made up of six very small 1.5v cells, wired in series. This is why they have a much higher internal resistance.

Ratings vary somewhat between manufacturers and lines of batteries. To get the manufacturers' specifications, go to their website.

Semiconductor devices generally require more than 1.5v in order to operate. The 9v battery is more convenient and much smaller than using multiple "D", "C", "AA", or "AAA" batteries. Of course, the penalty for the convenience is a shorter lifespan. However, some devices such as smoke detectors use so little power that they can operate for extended periods of time on one 9v battery.

Yes, that'll "get" you. You did prove something though - that you can't magnetize copper.

Sounds like a good plan.

Ahh, I see. Well, you wouldn't be able to measure the current, as it will be AC and most DMM's just measure DC current. Besides, it will be so low that there won't be much to measure anyway - and sample rate of the meter is so low that you probably won't be able to read anything.

15. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
But my DMM measures ac and dc or at least it has a button that say's
ac / dc on it?

As for measuring the current range goes from like 200uA to 10 A for current. I thought the mic current is in the range of 80 mA or so I forget now but whatever. That stuff is for later.

I still am confussed about the batteries. So if you have more volts you don't nessarily have more current for your batteries current rating.
Isn't the point to speed current up not slow it down.
If volts is the energy per charge then why have a battery do more work to move the same charge not to mention costs more 9 volt batteries are like \$4. I guess I don't understand why you wouldn't want to make a high volt , high current rated battery. As opposed to a high volt , low current rated battery. Is this something with the life span or power P = I^2 V?
I would still think you want high power with a high voltage battery.

Anyway I am assuming their is a reason for the lower current rating's for higher voltage batteries.

You did also mention internal resistance only comes into play when the battery life is almost done. But my 9 volt batteries where new.
And is the resistance in the copper wire even much smaller the the resistance in the battey assuming we are at room tempature.

It is odd that I didn't see any current rating's on the packages. UH?

16. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Actually, I don't know what make/model DMM you have. Inexpensive meters don't have AC current. I gave up on buying expensive meters after I had a couple of them go kaput after just a couple years.

The mic current would be on the scale of uA's.

Well, you have voltage, and you have Amperes.
Voltage = EMF (Electromotive force) = pressure.
Ampere = current = volume of electrons.
You need both to do useful work.

There are quite a wide selection of batteries available.
They do make reasonably high voltage, high current batteries. You can find one in the family car; 12.6v lead-acid. They can put out a lot of power. However, I wouldn't want to power a portable radio with one unless I had to.

It's because of the multi-cell construction. Resistance in series is additive. Check out our online E-books.

The resistance of the wire is VERY small. 10 feet of AWG 30 copper wire has a resistance of only 1.032 Ohms! You might not even have 10 feet of wire wrapped around your magnet's core. So, using Ohm's Law:
I = E/R = 9/1.032 = 8.721 Amperes
This is why a 9v battery won't last very long.
However, do the same calculation with a 1.5v battery:
I = E/R = 1.5/1.032 = 1.453 Amperes
Still a very heavy load for the battery, but if it's a fresh AA cell rated for 2500mAh, you'll be able to power your magnet for about 1.7 hours.
You'd be lucky to get 5 minutes out of the 9v battery.

Not really. It's likely that the batteries have a lower mAh rating that competitor's batteries. If they omit that information, but price the batteries lower than the competition, the uninformed consumer will have nothing to compare but price.

17. ### Audioguru Expert

Dec 20, 2007
11,208
1,329
Rechargeable batteries have a mAh rating that doesn't change much when the load current is changed. Disposeable alkaline batteries don't have a mah rating because the rating varies a lot by the load current.

Energizer alkaline batteries are made in the USA have a best-before date that is when it is almost dead. You can pick the newest ones in a store.

You can short a 9V alkaline battery with your coil of wire and its voltage will be almost zero. Then the current will be pretty low especially if the battery is old.

18. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
I forgot to mention something important.

Please do NOT attempt to connect your electromagnet to anything other than a small dry cell. If you DID attempt to connect it to something like a car battery, the wires would become white hot before they melted, and you could be badly burned.

19. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
I am sorry I don't get your battery explaination.

First you said that a 1.5volt battery would be better because it would
have a better current rating then a 9 volt transistor battery.

I looked up and a 9 volt battery is like 6 , 1.5 volt batteries in series.
So current is the same across all the internal batteries.

I can see why series would be better to get a greater voltage out of it.
But why the limitation on the current what is causing the great resistance
to keep the current rating's down to 150mA. You just said internal resistance isn't an issue and the copper wires resistance isn't an issue the what is the resistance keeping it's current rating down.

But I would think if a current is going faster it would increase the attractive force F = qv X B. That would explain why high current rating's would be better for creating a magnet force. However the magnetic field could still be small causing a weak force.

AHHHHH more current makes more since in strengthing the magnetic force.

I guess your not seeing my point why make a battey that does more work per charge (volts) and produces less current (Amperes C/s). Works harder to produce the same current or less current. If you wanted this effect use resistors.

But in any case I haven't studied much on batteries but it total doesn't make since from a mathematical perspective.

NOOOOOOOOOOOOOOOO!

voltage or potential difference is by definition energy/work per charge.
ampere = is what we measure current in and is = C/s.
current is the charge per second flowing thru a given volume.

Why do you say volume of electrons it's is not the volume of electrons
but the flow of charge per second thru the volume.

EMF = volts wrong .
EMF is a force volts is not. It is the work done per charge.
Work = force times distance .

When we talk about the voltage = integral E ds
(where E is the electric field )
The Force is the qE which is the EMF and the integral is the voltage or potential difference.

Many people also get screwed up on potiental energy and potential difference the only difference is potiential energy = integral q E ds
(i.e the fact of q )

This should make since to you. But if not let me know. I am a mathematician so I am good at the theory stuff.

Thanks for the battery and mic tips though. I would have been lost with out them.

And yes the AAA batteries are rechargable. So will it still work?