Step 2: Creating the Primary Coil

Picture of Creating the Primary Coil
Photo 50.jpg
The primary coil uses magnet wire, which is easy to get at RadioShack.
We will use magnet wire as the material for our coils.

Next we need something to create the 147.7 square wave AC signal. I saw videos on youtube like this one. Which uses a function generator. Sadly, these cost a lot of money, so i wanted to get a low cost one, that still did the same thing, just not as high of a frequency. This is great for what i needed. Cheap and simple.
This will be the main board to create the signal.

By using a pencil or nails on a 2 x4 and your magnet wire, you can make a pretty good coil. I did about 30-40 turns, depending on the thickness of your magnet wire. Magnet wire has a very thin coating on the top of it. To get this off you can light a match and put the magnet wire in the flame for a few seconds. Take the two ends of you coil and put it into the function generator on the top two screw terminals, one in each terminal. Polarity is not a problem right now because the signal will be AC. Now place your 0.02 uF film capacitor in parallel with the terminals you put the wire magnet ends into. Turn the function generator on and use your multimetter to get it to somewhere near 147-149 kHz by turning the potentiometers. Make sure the switch on the left of the board is set to square, and your good to go. The top to terminals will allow for an AC signal.

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john.hawes.965 months ago

I see a heck of a lot of wire for something supposedly 'wireless' .

evictor29 months ago

Aren't the exposed wires dangerous because AC is passing through them? How can this be insulated safely without affecting the resonant properties of transmitting and receiving coils?

asrivastava1010 months ago

Well you can use OP-Amp to create a square wave of desired frequency, just google it, its very easy to make as it looks from the diagram cz I have never made it myself just studied it as a part of my electronics course.

You can do the same using 555 timer though its a bit less easy as compared to opamp one.

gnimrezt882 years ago
Hi, may I know what component is used in the design for the primary coil? (The one connected with function generator and dc jack, voltage regulator?)
jose15222 years ago
Hi guys! I was looking for an alternative for the Frequency Generator Kit since its not available and I found that a astable circuit with a 555 timer can do the trick; however, i'm not sure about the Capacitor and resistor configurators... I used an online calculator to obtain a configuration close to the 147.7 Khz frequency and it turns out I can get 146Khz with a 470 ohm R1, 47 ohm R2 and 0.01 micro farad C . Can someone double check the math for me? Thanks!
Sorry, another correction. R1: 33ohms, R2: 470 ohms.
I just reallized that with a 33 ohm resistor instead of the 47 ohm one I get 148Khz frequency. Still, can someone double check it?
minu.14073 years ago
is there any formula to find out the number of turns of the transmitting and receiving coils used for wireless power transmission?
nzemke3 years ago
Ok so I get everything your trying to do but I'm confused as to what model of rectifier to use? Or if that is even what your using? I picked up a full wave brdge rectifier (GBL005) from that the correct thing to be using? Thanks ahead of time for taking the time to answer.
NeMewSys3 years ago
Hi, great article!!
Your 147.7 square wave AC signal generator just retired from the market, are there any alternatives?

How do you know wich capacitor to use to get that frequency? Could you show us the math?

Thanks ;)
there's a newer version of the kit that can still produce the same output:
hey i checked that link and that one was retired too anybody have suggestions?
Theres a possibility.
I haven't tried it yet but I plan on it.
I am also very interested in this.

Can someone point me in the direction of a kit I could use to generate the 149KHz signal?
heh can any1 send me the a perfect list of components required for it
The faster the list gets to me the better...
plz help on...
could you use a 555ic to replace the function genorater?
n_cleaner4 years ago
Can you tell me the company of MULTIMETER?
mgercak4 years ago
Can I have like just a list of materials I need to buy in order to make one that can charge an Ipod or something? thanks, my email is The faster the list gets to me the better.
when u mean ac signal do u mean a 555 push pull circut cuz i what to build me own gnerator so i can put it in a nice box thankx :)
The Function Generator is out of stock :( so I look for another and I found this one, Can I use it too?
Would some pre-wound RFID coils suffice for the job??? :)
memo26344 years ago
How do you go about choosing the frequency for the primary coil in the project? I'm assuming if the capacitor value is different, the frequency will be different as well.

Also you mention using nails on a 2x4 to wrap the wire into a coil. Is that done to keep the wire bunched in a tight group?

Based on the size of the coils, what kind of distance were you able reach? Lastly how many feet of wire did you end up using?

I'm working on a project for school that will implement this and it would help if I could get some quick help. Thanks
calidude894 years ago
Im very confused. Is the capacitance of the primpary supposed to be the same as the secondary coil? I only see one capacitor on the primpary. but you said you used 2 capacitors to make .02uf. Also the instructions differ from the pictures in value of capacitance. I purchased a function generator just for this project. I have 2 .01uf caps in series on my secondary coiil and 1 .01uf cap on my primary as shown in ur pictures, but it doesn't work.
redbloomer4 years ago
dude i've been inspired by your so i decided to do something like that. and i successfully made it.. thanks for your ideas..
TS19905 years ago
this instructable interesting and I am trying to build one one my own. I am just a beginner and I have some questions, would you please help me out?
Q1. why did you choose 147.7 kHz for the frequency?
Q2. you said the two coils should be in tune, what is it that affects the frequency of the secondary coil?
Q3. what waveform comes out from the other end, is it sawtooth or something else?
Q4. how efficient it is?

thanks :)
 can you give me instructions on the plug from the generator?
can you conect the generator to a usb plug?

please answer me soon
 (I'm a beginner at this)
in the circuit used in primary coil, what are the 5 ICs used? pls answer asap...
we'll gonna do this as investigatory project...
Algag5 years ago
 anyone thats metric (even though I'm not) the measurements of the 2 by 4 he is talking about is 38*89 (millimeters) 
gxb54435 years ago
how big did u make the coil?
Algag gxb54435 years ago
 as big as you want, i would say about 6 by 12 (inches) but you cant do that on a 2by4....well obviously
koopatroopa5 years ago
is there anything inside the coild? is it and electro magnet?
 a coil of wire with energy running through it creates an electromagnetic field

sk.mobeen5 years ago
what do you mean by 2x4....can u specify sizes in centi-metres or inches for both primary and secondary coils. for ex....primary(10cms x 5cms). please HELP.
Algag sk.mobeen5 years ago
 look at my above message

tubbsey885 years ago
Isnt yur cap a little counterproductive? Should it not be inline with the positive line, rather than spliced into both leads?
nahyah5 years ago
Would a primary coil and the receiver coil having similar loop size increase the efficiency of the power transfer? Since maximum efficiency would require the receiver loop to be in the center of the primary coil, that seems to make sense. Any ideas?
robotkid249 (author) 5 years ago
When i said 2 x 4 i mean nails on a 2 by four as on a piece of wood.
koopatroopa5 years ago
could you just plug this into some batteries instera of the genorator
jimvandamme5 years ago
Ya know, if you could get it to resonate somewhere in the 20 KHz range, you could use a secondary winding like the 5 volts out of an old computer supply. I've done it at higher power levels to make a VLF transmitter that went through 150 feet of solid rock.