Introduction - What is a stun gun?

A stun gun is a weapon that uses electricity to temporarily paralyze a person. The short

pulses of high energy cause the muscles to expand and contract very quickly, using up

energy and causing them to temporarily lock up. They are sold as self-defence weapons

in most european countries and the US. The British police will probably be using them

soon. Typically, the voltage range of a commercial stun gun is between 50kv and 300kv.

Background to the project

For the past three years or so, I have been trying to construct an improvised stun gun in

my spare time. It started out when I was searching for stun guns on the 'net, and then

started searching for stun gun circuits. I couldn't find any, apart from a few rather sketchy

patents. The circuits I found that claimed to be stun-guns were simply high voltage

generators that could put out a couple of thousand volts or so. While unpleasant, this type

of device would not have the effect of paralyzing the muscles.

I designed a couple of circuits of my own, and built one. Those of you who have been

following this project since it began will remember them. The first design was similar to

my current design. It used two transformers, one that would charge a capacitor up to a

thousand volts or so, and then discharge this into a transformer. I never built it, although

it is very similar to the current design. The second design (which is still on the site, the

HV generator) used a multivibrator to step battery voltages up to between 1000v and

1500v, and then use a Cockroft-Walton voltage multiplier to step it up to about 8000v.

The maximum output voltage using this setup is only limited by the number of stages in

the multiplier and the ratings of the components. Unfortunately, the output is still not the

high voltage generated by commercial stun guns, although it would be painful, and with a

big enough capacitor in the final stage could be fairly effective. The spark would be an

effective deterant, since a capacitor discharge is very bright and loud.

Self defence in the UK

One of the reasons I'm putting up this information is as a protest against British laws

covering self defense and weapons. In the UK, if you shoot a burglar, you'll get a far

longer sentence than the burglar (or rapist, you don't know their intentions when they

break in) would get if you'd left him to it; look at the Tony Martin case. I suspect this

would be the same if you stabbed or clubbed a mugger in the street. The attitude of the

police is 'don't fight back', or 'use reasonable force'. It's not going to be easy for someone

who doesn't deal with violence in everyday life to judge what is reasonable force to use

on a career criminal, who's intentions are not known. The police themselves seem to have

trouble judging what is reasonable force to use, given the number of fatal shootings of

unarmed people recently.

It is illegal to carry anything that could be used as a weapon, unless you have a good non-

self defense reason, such as a builder carrying a Stanley knife in his toolbox. The burden

of proof is on YOU, not the policeman.

Having said this, what are the chances of getting caught carrying a weapon? I rarely see

police patroling the streets, let alone the dark alleyways and paths that must be passed

through to get home for many people. They seem to be more interested in catching

speeding motorists, and raking in the cash from fines. CCTV is also a favourite. The

more cameras, the less police they need on the beat. When someone gets mugged or

raped, who cares if they couldn't defend themselves or that there were no police around?

The fact that the crime could have been prevented in the first place doesn't seem to

matter.

People who are against the use of stun guns and pepper spray (also illegal) would argue

that these weapons would be used by criminals. Personally, I'd rather be attacked by a

mugger wielding a stun gun than a mugger wielding a knife or gun. I'd also rather use a

stun gun to defend myself, rather than risk killing someone and getting a jail sentence.

This brings me to the handgun ban in 1997. There was no point at all, gun crime and

other violent crime has continued to rise regardless. It just shows how low politicians will

stoop to get cheap votes and momentary popularity, and how the public are manipulated

by the media for their financial profit. We are being disarmed and forced to depend on

the state for protection. Personally, I'd rather have the means to defend myself than rely

on someone else.

Just to clarify, I'm not anti the police at all. I just think everyone should have the

capability to defend themselves.

Anyway, rant over!

100% Improvised

The whole point of this project is that the device can be constructed easily, with readily

available components. There is no need to buy miniture high voltage transformers, that

are difficult (or impossible) to get hold of. All the components can be sourced from

junked consumer goods (although the UJT, SCR and enamelled copper wire would be

easier to buy than find). Unlike the previous design, the high voltage capacitor used can

be easily sourced from an old TV if a few modifications are made.

Intended audience

You don't have to be an electronic hobbyist to build this circuit if you're patient and

willing to learn. It could be a fun way to get into electronics! But it will be difficult, and

require a lot of effort. If you get disheartenned or frustrated, leave it for a couple of days

and then start work again. Unless you have a well stocked lab/unlimitted cash, there will

be a lot of waiting around for parts to arrive/be bought/found anyway.

I have tried to provide as much advice as possible, but it isn't intended to be a beginners

project.

Parts sourcing

Part Description Rough Price Equivalents Comments

C1 10uF 25v

Electrolytic £0.10

Any cap of

roughly 10uF that

will handle the

circuit voltage.

Readily available

C2 1uF 25v

Electrolytic £0.10

As above but

around 1uF. Readily available

C3 1uF 850v £4

Cap between 1

and 2uF that can

handle peak

voltage from

rectifier.

HV caps can be

found in TVs and

photoflash units.

Check the

voltage rating!

R1 220 ohm 1W £0.03 Roughly that

value, at least 1W Readily available

R2 1K ohm .25W £0.03

Roughly that

value, at least

0.25W

Readily available

R3 500K ohm preset

(trimmer) £0.50

Any preset of

100k or more. Readily available

R4 27K ohm 0.25W £0.03

Roughly that

value, at least

0.25W

Readily available

R5 100 ohm 0.25W £0.03 As above Readily available

R6 10K ohm 0.25W £0.03 As above Readily available

R7 220 ohm 0.25W £0.03 As above Readily available

D1-D8 1N4008 £0.10

Anything of

circuit voltage

spec for D1-D7,

D8 should be

1N4007 or better.

Readily available

Q1-Q2 2N3055 £2.50

NTE210, or any

NPN transitor of

about the same

power rating.

Readily available

SCR1 TYN810 £

2N4443, or any

SCR that will

handle this power

Many

alternatives,

check that they

level. can handle the

power.

UJT1 2N2646 £ ?

Standard item,

should be

stocked by any

supplier

T1 ~1:75 step up £- - See text

T2 ~1:95 step up £- - See text

0.125mm ECW £? Any ECW of

about that size Sold on reels

0.25mm ECW £? Anything up to

~1mm Sold on reels

Ferrite Rod 3+ inches long £? Any ferrite rod of

correct size

Scavenge from

broken AM

radio.

RM10 core kit

Ferrite

transformer core

kit

£2.50

Any ferrite core

of correct size,

including

torroidial.

Torroidial cores

can often be

scavenged from

scrap equipment.

If you can't find an electronics supplier (this won't be a problem in the UK), it will be

difficult as you'll have to find equivalent parts from junked items. If you can't find a

particular part, there will be many equivelants. I have listed some on this page, along with

things to bear in mind when finding others. By far the best thing to do is to buy

everything as specified, then you'll know it's all working fine and any errors are your own

fault ;-) There are many electronic suppliers (some mentioned in the links section) in the

UK that stock nearly all the parts needed.

The Circuit

The circuit was designed by c0deblue. It uses a pulse oscillator to step the battery voltage

up to several hundred volts AC. This is rectified, and used to charge up a high voltage

capacitor. The capacitor is forced to dump it's charge into the primary of T2 at a rate set

by preset R3, normally many times per second. T2 is a very well insulated open core

transformer would on a ferrite rod, that steps up the several hundred volts to many tens,

even hundreds of thousands of volts. This very high voltage creates a crackling spark

between the two secondary terminals of T2.

Construction

The following is a rough guide for people unfamiliar with building circuits. I've tried to

present it in a clear way, but you'll still need to think carefully. It's not a '1, 2, 3' list of

steps, you can do things in the order that you want. I hope that it will answer any

questions that come up when you build it, rather than provide a strict construction guide.

If you're used to building circuits, all you'll need is the schematic and stripboard layout,

as well as the information on how to wind T2. You might want to check out the

troubleshooting section, in which I've detailed possible solutions to problems that might

crop up.

If you use the parts that I have listed, you can construct it on stripboard straight away. If

you are using any substitute parts, it might be an idea to construct it on solderless

breadboard first (if you have one) to make sure it's all working.

Prepare the stripboard according to the layout shown in the diagram below by cutting it to

size and using a drill to break the tracks in the places shown. Note the arrow indicates

that the tracks are vertical, and the blue lines indicate jumps (wires connecting tracks).

Solder the components from the first 'stage' of the circuit onto the board. It's best to do

this in order of size, i.e. links, resistors and diodes first, then the preset, and finally the

caps and UJT. Doing it this way helps to prevent the parts from falling out when you turn

the board upside down to solder them in, since the components will always be resting on

the work surface. It also helps to bend the wires slightly before turning the board upside

down, jamming the components in place.

Note that the board in the photo is too small by one track (far right). This was a

design error!

These are the pin outs of the Semiconductors used.

The high voltage part of the circuit will not be constructed on the board in the

conventional way, to prevent any arcing between tracks. Arcing shouldn't be a problem in

a working circuit at the voltage specified, but I decided to take the precaution anyway.

The current will take the path of least resistance, and this will be through the wiring

rather than the air if the circuit is working properly! To give an idea of the breakdown

voltage of air, a rough rule is 1000v DC per mm (depending on electrode shape). Solder

the diodes together to make the rectifier as shown in the next photo. Try to make the unit

as compact as possible.

Solder the SCR onto the underside of the board. Solder R7 and D8 directly onto the pins

of the SCR according to the schematic.

Now solder the rectifier onto the underside of the board, leaving a few mm space between

the pins (except the earth) and the board tracks. The complete underside is shown here

(with wires; the photo's weren't taken in sequence):

Winding T1

T1 is wound on a small closed core ferrite transformer. The turns ratio of the primary and

secondary will depend on the voltage you wish to get out. To get out 675v from 9v, I

used a transformer with 1500 turns on the secondary and 20 on each of the three

primaries (1:75). The only reason I used so many turns on the secondary was because I

already had one lying about ready wound. It was a very tight fit, so I recommend using

around 1125 turns on the secondary and 15 on each primary. This will give the same step

up ratio, without much (if any) loss in efficiency.

The secondary is wound onto the coil former (bobbin) first. I used 0.125mm diameter

Enamelled Copper Wire, but this isn't critical. So long as all the winding will fit, any

guage wire can be used. Solder the end of the enameled copper wire onto one of the pins,

and wind 1125 turns onto the bobbin. Try and keep it fairly neat to give even turns

distribution and allow plenty of space for the primaries to be wound on afterwards. When

done, solder the other end onto another pin. Check for continuity with a multimeter. If

there is no current flow, re-solder the wire for slightly longer than before (to melt the

enamel). Wind a few layers of mylar tape onto the secondary to provide insulation.

Wind the primaries on in the same direction as the secondary. I used 0.25mm wire,

anything up to 1mm can be used without taking up too much space. Solder the ends of

each primary onto pins on the bobbin. You'll need to remove the enamel using some

sandpaper from the ends of the primary wire to ensure a good connection, as it's thicker.

Final Circuit Construction

Solder some wires onto the base and emitters of Q1 and Q2, and solder these onto the

board. Solder wires onto the cases (collector) of the two transistors, and solder these to

the appropriate transformer terminals. Solder the other primary connections onto the

board. Solder the secondary terminals onto the inputs of the rectifier.

Attach the capacitor to pin 2 of the SCR. The circuit is now complete, apart from T2 and

the power connections/switch.

At this stage, you might want to test it to make sure it's working. A car ignition coil

works well as a substitute for T2, although it won't give such a powerful output. Attach a

wire to the middle terminal, and attach an earth to one of the others. Connect the

capacitor to the remaining terminal, and adjust the center terminal wire so that it is about

15mm from the earth terminal. Connect up a power source (a 9V battery will do), and

you should get a spark arcing from the center terminal to earth. If you don't, adjust preset

R3 until you do. If you still get nothing, go to the troubleshooting section below.

Constructing T2

T2 is an open cored ferrite transformer. This means that the ends of the core are not

connected, as they are in T1. You will need a ferrite rod, which can be found in an AM

radio receiver (includes LW, MW etc). T2 will take several days to construct, so be

patient!

Insulate the rod with around 8 to 10 layers of mylar tape. Spray the tape with a layer of

acrylic spray. Wind 200 turns of thin (I used 0.125mm) ECW onto the rod, securing each

end with some tape. You must leave at least 1/2 an inch space from the end of each

winding to the end of the core, to avoid arcing.

When constructing my transformer, I sprayed one coat of acrylic spray onto each

winding, and insulated it further with 5 layers of mylar tape when the acrylic spray was

dry (usually one hour).

Leave 1/2 an inch of wire trailing from the end of the winding. This is not easy to

explain; think of the wire running out of the end of the layer of turns, the layer of turns

being covered in tape, and then running back to start the next layer of turns on top of the

insulation. I have drawn a diagram to try and explain it:

The number of windings you have will depend on the voltage you wish to get out for the

voltage you put in. I have a total of 3800 turns on my transformer, with 40 turns on the

primary. If I were to make another one, assuming the 750v input, I would use around

2000 turns on the secondary and 20 on the primary. I initially operated my transformer

with 250v pulses, but I then increased the input to 750v. At 20 turns on the primary, the

insulation broke down straight away. Fortunately I was able to repair it without re-

winding the secondary.

When you have wound the final winding, spray around 4 coats of acrylic spray onto it,

and further insulate it with 14 or so layers of tape. This is a rough guide; I don't know

exactly how much to use.

Attach some wires to the ends of the secondary winding. You might want to do this at the

stage (below) when you apply the Silicone sealant, since it can be used to secure the

wires.

I then took a piece of paper and wound it around the transformer so that it extended about

1/2 an inch beyond the end of the windings (including the trailing wires). I soaked this in

acrylic spray, and left it to dry. This was wound back onto the transformer, and secured

with another 5 layers of mylar tape.

The primary is then wound onto the transformer, above the secondary winding. It is

secured with mylar tape. I used 0.25mm wire, as with the secondary anything up to about

1mm is practical.

The secondary requires additional insulation at the ends of the windings. Due to the spray

saturated paper, there will now be a cavity at each end of the transformer. This must be

filled with Silicone sealant as thoroughly as possible, no air bubbles must exist. This is

left for 24 hours to cure fully. The next photo shows the sealant at the end of T2:

Testing

The primary of T2 is now connected to the circuit as shown in the schematic. Place the

two terminals of the secondary winding fairly close together (maybe 5 to 10mm). Power

up the circuit, and adjust R3 until you get some sparks! Power down the circuit, and

move the electrodes to around 3/4 inches apart. You should get a nice loud arc, firing at

between 3 and 10 times per second. I wouldn't advise moving the electrodes more than an

inch apart, as this could cause internal insulation breakdown.

This photo shows the circuit connected to the cap and T2.

Housing

I'm not going to provide much information on putting this into a case. I haven't put mine

into a case yet, because I haven't had time. I have 'shaped' the completed device to allow

it to fit into a 12 inch length of 40mm (outside dia) PVC waste pipe. I will mention some

things to bear in mind:

Make sure none of the components metal parts are touching, particularly pay attention to

T1 and Q1/Q2. You may need to apply mylar tape to the cases and insulate the terminals

with Silicone sealant.

Keep all wires to the minimum length required. This makes a neat circuit, and will help

the device fit into the case with ease.

T2 will require some additional insulation of the wires, since they will probably be held

flat alongside the transformer (depending on your intended case). I used standard

insulated wire for primary and secondary leads. In addition, I added several layers of

mylar tape to the primary wires, and I used some heavy dute mains earth cable insulation

for the secondary wire that I had to have flat against the transformer (the second one

simply comes out of the end, so it isn't in contact with the outside of the transformer).

Modifications to Voltage

If you can't find all the parts listed, you'll have to look for equivalents, sometimes in

junked items. If you can only find a capacitor of a lower voltage than that required, you'll

have to slightly modify the circuit to keep the voltage generated by T1 below that value.

This doesn't have any effect on the final output voltage if you change the ratios of both

T1 and T2. Some advice when changing ratios: keep the number of primary turns above

about 20 on T2 and 10 on T1, otherwise the coil will not saturate.

Troubleshooting

There are many things that can go wrong with electronic circuits in the construction

stage. In most cases, they need a little tinkering to get working. I've provided a short list

of likely problems. If you have any problems and are REALLY stuck, email me and I'll

have a think (if I think you've tried hard enough on your own, I'm not running a technical

support service!).

If you've had trouble getting it working but solved the problem, I'd like to hear from you

so that I can include it here.

Q. There's a buzzing noise, but there's no spark!

A. It's probably charging up (if the buzzing noise increases in frequency over time) the

capacitor, which is good. Try adjusting R3 from one extreme to another. If there's still no

output, try triggering the UJT manually. This is accomplished by touching a wire from

the positive supply rail to pin E as shown in the pinout diagram. If there's no spark, check

all connections around the UJT. You may need to replace the UJT. If there's a spark,

you'll need to check the wiring of R3, R4, R5 and C2 (the UJT triggering block), and

possibly substituting different value components (R3 and C2). If there's still no output,

check the rest of the connections in the circuit block around the SCR. If there are no

obvious faults, there might be a dead component (most likely the SCR) in the HV stage

which will need replacing.

Q. The buzzing noise doesn't increase in frequency over time, and there's no output.

A. The capacitor probably isn't charging up. Check that D8 is connected properly and

round the right way. Make sure that the T2 primary is connected properly.

Q. The circuit's dead!

A. If there is no buzzing noise, it means the pulse oscillator isn't working. Check all

power connections, then check all component connections. Make sure that the T1

primaries are connected properly to the correct places! By far the most likely cause of

this is a wiring/soldering error, or a component is round the wrong way etc. Did you

connect Q1 and Q2 properly? If the circuit is constructed on stripboard, run a sharp knife

along between neighbouring tracks on the underside. There are often shorts that are

difficult to see due to tiny strands of solder joining tracks, the knife will remove these.

Q. Could it be T1?

A. Yes! Use a multimeter to test each winding for continuity. If there is none, re-solder

the connections made at the wire endings. If there is still no continuity (especially in the

secondary coil) you'll have to re-wind it with new wire :-( Also check to make sure

windings aren't shorting each other out. If you find continuity between any windings,

you'll have to check the connections carefully. If it's a break in the insulation (unlikely),

re-winding is required.

Q. I've tried everything, but it's still dead.

A. If all the wiring/soldering is fine, then it will be a dead component. The most likely

culprit will be Q1 or Q2. Resistors and capacitors will usually be visibily damaged if they

are dead, but transistors rarely are. If you have a multimeter you can test them, if not then

you'll have to buy a new component(s) and test replace the suspected damaged one(s).

Advice on use

As of yet, I haven't tested it on anyone(!). If I have the misfortune to have to use it, I'll

share the results. In theory it should work just as well as a commercial stun gun. What I'm

trying to say, is that I make no guarantees. Even commercial stun guns aren't always

effective according to some people. While it may work well to immobilise a 9 stone

junky, I wouldn't want to use it on an 18 stone bodybuilder. What it will certainly do is be

a deterant. The spark is bright, especially in the dark, and it is very loud! You may avoid

a fight, especially if your attacker isn't a seasoned thug. They might go away and find an

easier target. That's the theory anyway ;-)

Future Modifications/Misc thoughts

This circuit is similar to my first ever design, which I abandoned long ago because I

didn't think it would work. The differences being that it used a less efficient oscillator to

step up the battery voltage, and it used a spark gap instead of an SCR. At the time, I had

no idea how to construct/obtain a high voltage transformer (T2).

Anyway, for better improvisation, a spark gap could be used instead of the SCR/UJT

combination. The disadvantage of a spark gap would be that the electrodes would soon

oxidise, requiring that the gap be replaced eventualy. If you are familiar with electronics,

you may want to try this.

At present, the device is putting out between 2 and 3 joules of energy per second. This

assumes that the capacitor is charging up to around 750 volts on each cycle, something I

can't measure because I don't have a CRO. It also assumes around 8 or 9 pulses per

second, and good transformer efficiency. A commercial Taser puts out around 6J per

second. I would like to construct a higher powered version in the future, that puts out

between 6 and 10J per second, at a slightly lower voltage (no more than about 50Kv). I

would accomplish this by using a higher voltage cap.