Fly swatter stun gun.

Hey guys.

Lately I was obsessed with making a stun gun.

I was particularly interested in fly swatter for the source of high voltage due to being easy to get and very cheap compared to using other high voltage circuitry (like from arc plasma lighter  or plasma globe driver.). It cost me around USD4 for a fly swatter compared to plasma globe (USD8), or arc plasma lighter (USD40) and I also dont have to wait for weeks to get it since its just available at the store in front of my house. (all prices are converted to USD from local currency)

Prior to this I have experimented with salvaged transformers and my self-made cockroft walton multiplier and oscillators (ZVS, 555 timer, joule thief) for making a stun gun but all gave disappointing results such as very thin arc (low current) even though the arc length was quite impressive. This is because for all these designs, I utilized usual 9V batteries which does not give enough current (hence power) to the final output due to its considerably high internal resistance compare to the load circuitry resistance (which subject to its design and chemistry). To add to this, the salvaged transformers were not optimized for the operating point I used.

Based on research I found out that the only optimally designed transformer for stun gun is flyback transformer. Flyback transformer is not only the one you can salvage from old CRT monitor, but the one miniaturised as in plasma globe driver or fly swatter and sometimes appears indistinguishable from common charger transformers (flyback transformer also available in a core-type design instead of the usual shell-type design as in CRT monitor). This type of transformer was designed so its ferrite core will have low coercivity (easily magnetised and de-magnetised to reduce hysterisis loss) and low leakage inductance at high frequency and generally has the ability to step up voltage lower than 10V to several thousands volt.

Fly swatter came to my mind to solve these two problems; getting high current and efficiently transforming voltage lower than 10V to several thousands volt. The reason behind high current from fly swatter is because of the battery it utilizes (which can supply high current at particular voltage) which I reckon is a Lithium polymer rechargeable battery and the specialized step up transformer which intentionally designed for increased efficiency at high voltage and high frequency operation. To my surprise, the voltage supplied by the battery is just 4.25V.

Fly swatter usually output around 1 or 2kV direct current which is sent to the mesh . You may Google and Youtube around to find out how fly swatter looks like. At first glance it seems like a usual tennis racket where the only difference is that the mesh is supplied with high voltage to give a fatal jolt to bugs (which is the primary purpose of its invention, hence the name).

Below is the circuit I adopted (only the high voltage circuitry part) for the fly swatter stun gun;

In the video below, the white stick is the handle of the fly swatter that contains the oscillator (I have removed the wire meshes). Two protruding wires (red and white) are the high voltage direct current output which originally attached to the removed wire meshes. The white plastic former is the spark gap ( I punch a common tape plastic former with two screws which were distanced less than 1mm apart). I found that the smaller the spark gap, the fatter the arc at secondary of high voltage pulse transformer which implies that the transformer can optimally operate at high switching rate (the lesser the spark gap distance, the higher the switching rate). The black taped bulky cylinder is the high voltage pulse transformer, homemade (description in the circuit diagram above).

The length of the arc at the secondary of this transformer is around 1cm (corresponds to voltage around 9kV to 10kV). Enjoy the video!

If you are impatient in waiting the video loading, I attach the final result snapshot below;

(the Powerball (green bulky stuff) and the tape are to fix the high voltage wire terminal in places)


Until next time!

Flyback arc driver circuit

Hi everyone.

This post is just a revisit on the Cockroft walton multiplier (CW) discussed before.
I utilised it as an input into the flyback transformer to see how the output looks like.

Some changes were made; I tweaked some component values on the oscillator part so the circuit operates at resonant frequency of the charger transformer (where it rings and produced highest possible output peak voltage as an input into the CW multiplier).

The video below is the outcomes;

The CW is 8 stage with ceramic capacitors (value stated in the circuit diagram below).

The spark produced is around 1.5cm to 2cm in length and is a high voltage direct current.

That's it.

Modified ZVS oscillator with centre-tapped/ double capacitors

Hi everyone! Finally I m back after around 3 years on hiatus... I was so busy with my job thus I have no time for experimentation, which without experiments, nothing to update on this blog.

Btw,  recently I have some time to come back to analysing ZVS oscillator which I have tested before. 

New problem struck me on how do I connect any salvaged transformer from electrical appliances to ZVS whereas the transformer is having single winding primary and not centre tapped one?

To solve this, I have made a modification on the original ZVS driver; by swapping the centre tapped coil with centre tapped capacitor/ double capacitors. Which means that, this new driver's output can be fed directly to any primary of salvaged transformers which mainly consist of single winding primary and not the centre tapped one.

 Here is the modified ZVS circuit;

The frequency of oscillation is determined by the capacitances of two capacitors, C1 and C2 and the inductance of the primary winding.

 Thats all!

Simple metal detector.

Hi everyone

This time I m gonna show you how a simple metal detector works.

I will be using the oscillator circuit and the coil transformer in the previous post, which I have modified it into a simple metal detector. The circuit is shown below:

The LED is made an indicator for the detector. The coil transformer is the detection coil. Object is put into the centre of the coil for detection.

I have tested this detector with different materials and got several results:

When I inserted the metallic object such as screwdriver or scissors, the LED dimmed.

However when I inserted a ferrite rod (which is not a metal), the LED brighten up.

Here is the video:

Note that the ferrite rod increases the LED brightness just a little, but if I connect the secondary winding of the coil transformer to the voltmeter instead of connecting it to the LED, the secondary voltage indeed increases but it is not sufficient to make increasing brightness of the LED apparent to the eyes.

The detector can be improved by using circular (disc) coils as the primary and secondary winding of the coil transformer instead of using the cylindrical coil transformer as I am using, and inserting the object to be scanned in between the discs.

The detector works by the principle of different core material for the transformer.

Any object inserted into the coil transformer will be automatically assigned as the core of the transformer.

If you insert a ferrite rod, it will act as the core. Since the ferrite rod has high magnetic permeability, the magnetic flux around the coil transformer finds a less reluctance (magnetic resistance) path, which is the ferrite rod, to flow through. Hence, the field lines reinforce together, reducing the lost magnetic flux and hence, making the LED shines brighter.

However if you insert a metallic object, it will create eddy current within it as a reaction to the changing magnetic field it resides within. This eddy current will in turn create other changing magnetic fields that oppose the magnetic field the metal resides within (which is the magnetic fields of the coil transformer), cancelling the magnetic fluxes together and hence generate less voltage across the LED, dimming it as a result.

This detector, although works, is not suitable for practical metal detection since you have to put the tested material/metal into the coil, which is not practical if you want to detect any hidden metal across a flat surface. Therefore, for that purpose, the coil needs to be flat as well to facilitate smooth scanning of the flat surface. Hence, flat coil transformer is frequently used in the actual metal detector design.

Flat coil is like a mosquito’s coil, and it is very hard to make by hand, and requires special tools and materials. That is why I resorted to using cylindrical design like the coil transformer.

I think that’s all for today. Thanks for reading.

Lighting fluorescent bulb using 9V battery (Part II)

[To read Part I of this article, click]

As you have seen from Part I, I have used flyback transformer in the circuit to light up a fluorescent bulb using 9V battery.

Actually, I want to keep the whole circuit as simple and constructable as possible, where I want to remove some components that are rare, difficult to find such as flyback transformer and ferrite rods. As CRT tv and pc are obsolete nowadays, flyback transformer gets even rare and more expensive.

Therefore I set a rule when designing a new lighting strategy; no flyback transformer, and no ferrite rods !

I planned on using just the tissue roll former and copper wire and make them into a simple transformer.

Here how it looks like:

The red wire is primary while the yellow wire is secondary. Notice there is a centre-tapped wire (red)

at the middle

I wound the secondary first on the former, about 8 layers of winding and then two layers of primary on top of it, with centre tap wire. The copper wire I have used is SWG 27 (0.4mm thickness). The tissue former dimension is 3cm diameter and 5 cm length. The design is not too strict and you may decide by your own on how many number of layers/turns you want to make for secondary/primary. Its damn try-and-error thingy. When I made it I just do it as I like and no engineering calculation was done. 

The resulting secondary voltage from this transformer is not enough to light up the fluorescent bulb, though. It can only light up an LED. Therefore, I stepped up the voltage using a rechargeable battery charger transformer I have used before. Well, I am still havent break the rule cuz I am not using flyback transformer.

The rechargeable battery charger transformer, utilised as step up transformer to elevate the output voltage from the coil's secondary

The resultant voltage from the battery charger transformer can eventually light up the bulb.

Overall circuit, with the light bulb being light up involving both coil and transformer. The driving circuit is the same as used in Part I of this article, a Joule thief.

Close up.

By using this strategy, you can use items that is easily available such as copper wires and charger transformers and dont have to find old CRT tvs to salvage the flyback transformers from them, or spending dollars to buy ferrite rods. You also dont have to buy a new disposable camera just to get its flash transformer for this project.

You may also use other transformers other than battery charger transformer, such as those in electronic lamp ballast, and cellphone charger.

Thanks for reading. 

Lighting fluorescent bulb using 9V battery.

Dear everyone I am back!

Lately I ve been testing this circuit. Its called 'Joule thief' and I tried using it to power up a fluorescent bulb using just 9V battery.

Here is the schematic I ve been using:

Or if the above photo is not too clear...

I have used flyback transformer salvaged from old CRT television. The primary coil is centre-tapped with 8 turns for each coil. 2N3055 is used as switch due to its high power rating.

Choke 34uH) and electrolytic capacitor (100uF) are used to provide constant current and voltage to the primary coils.

Output voltage from the secondary winding of the transformer is capable of driving small fluorescent bulb.

The photos explain my project more:

My setup. Battery at the lower part, the circuit, flyback transformer (bulky black chunk) and the farthest stuff, the fluorescent bulb.

I have removed the circuit board below the bulb and just taking the bulb. I connected a wire to each of the terminal. Each is then connected to each terminal of the flyback transformer's secondary.

The video. 

 The bulb appears quite bright in the dark for 9V supply.

I tried adding a capacitor (1uF, or you may try any value) across or in parallel to the 500 ohm resistor and guess what, it made the bulb shines brighter! This time I ve changed the bulb to a longer one to spread the lights wider but I think this capacitor effect also works for the smaller bulb.

 

The longer fluorescent bulb

 

As usual I removed the adds on from the bottom (which comprises of a capacitor and a fuse-like stuff) and connect the bulb's terminals directly to the output of the flyback transformer.

 

 Before lighting up.

 

Before adding capacitor.

 After adding a capacitor.

Thanks for reading.

Update (11 Apr 2013): I tried using my homemade flyback transformer and the circuit works, with an additional capacitor  (around 0.1uF) attached between each end of the primary winding. Here is the photo:

The flyback transformer (homemade) that I have used:

The vertical ferrite rods are longer this time compare to the previous ones cuz those shorter ones are being used for other projects.

Homemade earphone

I have recently made my own homemade earphone from balloon piece, button magnet and copper wire.

The principle of operation behind an earphone is so simple; vibrating magnet in a varying magnetic field will produce sound. Given this understanding, you can start building your own earphone using materials around your home (except for button magnet and copper wire, I guess).

Before I move further, here is the photo of my finished homemade earphone:

You may not understand the photo, so I included here my plans of making it:

 

I used neodymium button magnet for this project and 36 SWG copper wire. Neodymium magnet is strongest man-made magnet, it will response to small magnetic field generated within the copper coil in the earphone. So in other words, by using this magnet, it makes my earphone more sensitive.

The principle of operation is as explained in the above photo.

The quality of sound is akin to that of real earphone, but not to that of speaker. The bass and low frequency sound are very clear, perhaps because I used rubber piece cut from balloons (so it is more elastic as a diaphragm and vibrate easily at lower frequency compared to plastic diaphragm which is quite hard to vibrate at that region of frequency)

I really wanted to put a video here to show that it really works, but my Iphone camera cannot record low strength sound (from earphone) very well. Anyway, it really works and if you dont have earphone, you can make one by just using a magnet, copper wire and some stuffs laying around your house.

Good luck if you wanna try it.

Update (8 July 2012): The earphone can actually functions as a loudspeaker, but with significant audio distortion compared to commercial 8 ohm loudspeaker. In the following video I connected the homemade earphone to the LM386 audio amplifier which amplifies the audio input from my laptop (connected using 3.5mm jack audio cable, the yellow pins with black cable in the video). I think this homemade earphone is just best serving as earphone since it distorts audio signal at higher volume.