Author Options:

Square Wave Generator (For Resonant Air-Gap Transformer) Answered

I've decided on a project for the new year that is ~~less likely to lead to sterilization~~ better than my old project (which was a homebrew x-ray machine). My new project is something to wirelessly power some LEDs. I've done some research (read as, YES NACHO, I ALREADY GOOGLED IT!) and looked at puffin's unfinished instructable on IPT (it helped a lot). What I've found out is that to start, I will need something to generate a square wave AC signal. The circuit I decided on is a 555 multivibrator. One of my friends let me copy the schematic from his notebook. I've got a couple of questions still (and I hoped you guys could help). 1st. (Dumb Question) That symbol in the second picture is ground, right? 2nd. Once I build the multivibrator, how would I hook it up with the rest of the circuitry for my air gap transformer? (ie. where would the outputs on the circuit be?) 3rd. What does that symbol (it looks like it should just be a resistor symbol), next to the words speaker or other circuit mean? Is it just a resistor or is it actually the outputs I've been looking for? 4th. Is there anyone who has successfully done a project like this before (recently)? Thanks in advance for any help.


1) Yes
2) Pins 3 and 1. See BinaryBoy's comment.
3) It is a resistor. It represents the resistance of whatever load you use. If you can identify the load, that will point you to the output. In this case, the load is connected to 3 & 1.
4) Way too long ago for me to be a whole lot of help.
. The nature of your questions indicate to me that you've already done your homework - no need for one of my tirades. ;)
. Having to ask #1 doesn't mean you're dumb, merely ignorant. Ignorance you can fix (ask questions); can't do much with dumb. "The only dumb question is one you don't ask." "We all start out knowing nothing." &c.

 Hey, reading the last statement in your answer inspired me to ask you this, as I would feel stupid if I asked most other people (most other people don't have the same respect for other's ignorance as you) that being said:
Is the ground for the negative side say, a 9 volt battery, so obviously DC volts, or is this supposed to use 9 volts AC and the ground is just a ground? 

.  In the case of the schematic above, ground is 9V less than +VCC, but does not have to be at Earth potential. In theory, +VCC could be 109V and "ground" at 100V, but this could make interfacing with other devices difficult. Using an Earth(ed) ground means we all have a common point of reference.
.  +VCC is DC. You get pulsed DC between pins 3 and ground (pin 1).

 Sweet, thanks for the help, just another question, if I were to build this circuit and use a 9 volt battery then where would I put the negative lead from the batter socket, (would it go to the ground)? 
-Thanks again!

.  Yes, pin 1 = negative terminal of the 9V battery.

 Ok, thanks again for the help, their kind of primary things, but I need to understand it nonetheless. 

Oh, and do you mind if I ask one more question? Is there any good way to test to see if it's working? (Can I just hook up an LED?)

Yes there are ways to test if it is outputing... and one way is to hook the Load to an 8 ohm speaker. Do you know the frequency of the square wave this circuit will generate? Do you know what you desire as a frequency?

This will determine what values to use for RA and RB

Okay, cool. Thanks! I'll go calculate the numbers to see what value of resistor will give me around 250 kHz.

. If you're using an LED for testing, don't forget the current-limiting resistor. . If you're going to use a speaker for testing, aim for 5-10kHz. You can't hear (and the speaker probably won't reproduce) 250kHz. That will tell you if the basic circuit works and then you can change components to get the desired freq.

Oh yes, I forgot about the hearing range oops LOL

you can change the 0.047 capacitor too. less capacitor = more frequency

you aint gonna hear anything above 15 - 18 khz in ambience / about 22 khz in complete silence. im also unsure if 555 works at 250 khz

Ok. I'll probably end up using a lower frequency for the actual project.

You forgot one aphorism, Nacho: "There are no stupid questions, only stupid people." (Mr. Garrison).

For the humor-impaired, no, that was not aimed at Gjdj3. All those questions are excellent.

Thanks for your help! I had a feeling on number one because ground made sense in the circuit there, but it didn't look like a normal ground symbol.

hey that's just great... can u tell me what are the votage and curret levels in the primary ? and sorry for bothering.... also do you have a diagram of the push-pull circuit you used between the 555 timer and the primary ? congratulations, nice work !

Sorry it took so long to respond! I still haven't been able to get my project to work in a fully resonating state so my answer might not be fully accurate. A better answer might come from plasmana's response a few comments below.

yeap thanks i guess i'm gonna have to be patient... the thing is i made a 555 to work... as i got variable resistors (1 Kohm and 2 Kohm) and trimmers, i can tune a certain range of frequencies by adjusting them. although there's a problem: i got a 9V - 0.035A output, which i think is too weak to feed a primary and so i would need more current to make it work. am i right ? besides, i am also a bit confused about the concepts of "inductive coupling" and "reactance coupling"... well i think this is the big picture... thanks !

I have very recently have been working on my wireless project, unfortunately, I could not get it into resonating mode, it just kinda work, I will try post an video ASAP.

Cool! I'm excited to see it. It's wierd how we're working on a lot of the same projects. haha.

Sorry for he long delay, I lost the firewire to download my videos, but I found it! :-)

Anyway, here is the video of my wireless power project.

Curse you for beating me to it! But nice job! Just one question, what was your power source? (I lied, I have another question. What did you use for your signal generator?)

Don't curse me just yet... :-) Nothing is resonating here, it is an inefficient design that somewhat works.

12 volts from the SLA battery.

(Haha!) A 555 timer with a crude but simple push-pull circuit (the blue film capacitors and a large black inductor is part of it).

Some more information if you need it:
  • Drive frequency - 25KHz.
  • Primary coil - 40 turns using 18 AWG wire.
  • Secondary coils - 100 turns on bobbin core using 40 AWG wire.

Okay, I'm almost done with my version and I'll probably publish it here soon. Are you going to publish your version?

That is cool! And about my version, I am not too sure if I want to publish it because I made it before I joined instructables, so I cannot show it being made step by step and it does not resonate. Does yours resonate?

About the resonating... I got mine to work in a sort of inefficient state without resonating. Now I'm trying to change the circuit to get it to resonate. I added the necessary inductors and capacitors, but several problems hit me (Both caused by my brother). First, he was playing around on my bench and accidentally shorted the batteries I was using. Then (and this is the more serious problem), he ruined my coils. Now I have to order more wire from the internet. I'll know if it works or not in a week or two when I can remake the coils.

Ouch! That is too bad... :-(

Luckily, I told my brother and sisters about some of my stuff that is very dangerous if misused. But they now think everything I have is dangerous, and they don't even dare to enter my workshop... :-)

You should try tell your brother that some of your things is dangerous, (like it will shock you if you touch it). It may increases his fear of touching your things...

Yeah, that might work. Haha, he's still afraid of disposable cameras since I shocked him with one.

I was wondering why there wern't any capacitors... That just inspired me to rekindle my wireless energy project, but my project list is long, as well my homework list...

They are capacitors, those two large 'blocks' on the breadboard, they are used to create full wave AC for the primary coil.

I meant on the secondary. Also, how'd you create a sine wave?

I don't even know whether I am generating sine wave or square wave AC... :-) I need to check it with my oscilloscope when i get a chance... And the capacitors on the secondary coil, I was just lazy to put them on. But I did put a small capacity rating capacitor (I can't remember the value) one time, and I managed to get more output from the secondary coil.

oh, and on a seperate but related note, I got a function generator for my birthday (well kinda, I can't open it till my birthday, but i picked it out), and I was wondering, what's the best way for amplifying the signal. I can't drive a coil directly from it. Speaker amplifier?

No kidding! you are going to get a function generator!! >:-( I want one too! At least, I have been given an very old oscilloscope for christmas from my school. :-)

most have 5 V 50 ohm output. thats about 100 mA at short circuit and 50 mA at max power output for more a speaker amp is great but may clip if your input voltage is too high for much more and square wave just use a transistor. 2N3055 can pass several A at quite high V

so, if Clipping isn't a problem, do you think it's a good way to go?

i guess yep watch out for dc blocking capacitors and for overheating

got a spare computer hard drive cable ? wind with it. mismatch the ends by 1 pin and you have 2 very long coils very easily. now connect them in series floppy cable is ok too but you may have to rewire the end where the cable flips over

Haha, not yet.... There are no arc coming out of the coil... :-(

a resonant air coil? do i hear tesla? btw: someone please help me with my tesla coil.

yep its earth you usually dont have to connect it to real earth though the square wave exits on entry 3 of the chip. you connect your load instead of the resistor ac loads (speakers or coils etc) need a dc filtering capacitor (10uF in this example). dc loads (like leds or power transistor) you connect directly to the chip in your project youll probably use a power transistor to amplify the current. remove the capacitor and instead add a resistor to limit the transistor base current (usually few hundred ohm for power transistor at 5 V. check with your transistor specs)

I've fidled with the idea, but problems I ran into: I'm pretty sure that a sine wave is best a sine wave is hard to generate a sinewave is hard to amplify (compared to a square) I estimated that one would need about 48 volts at a couple amps to drive anything useful on the otherside. yeah....

a friend of mine has a battery free wireless computer mouse. the pad plugs into usb (2.5 W max) and its sufficient to light the led in the mouse from 20 - 30 mm distance can you imagine the magnetic power lines created by the pad ? well i think that can give a clue on the distance untill which its still functional square wave makes pulses of high voltage on the coil that recieves it. it can actually be usefull a wave like this \/\/\/\ (1/3 - 2/3 the supply) exists on the capacitor of the 555 (entries 6 and 2). you can use it too (thru opamp) if you want