LED flasher using relays.

Hey guys.

Just wanna share circuits using relays to flash LED. I researched and found two different designs which both utilises only one relay and some capacitors .

The capacitance of the capacitors is quite big (around 1,000 uF and higher) to yield a low frequency flashing ( if too high then the LED will not appear flashing since it flashes very fast). I did'nt buy the capacitor, instead I salvaged from an old CRT monitor laying around in my room.

Flip-flop or bistable latching using relays.

Hey guys,

Since I have plenty of relays laying around and dont know what to do with them, I decided to test if using this relays can mimic the flip flop actions of solid state devices such as transistors.

I know that there is already a latching type of relay made into a single package 'latching' relay in the market, but since I have different type of relays which functions as mere simple switching conveyor, I have to use my brain on how to configure these relays into a circuit that can mimic flip flop action.

I came up with two different types of circuitries; design A incorporates two different contacts for SET and RESET actions while design B incorporate only single contact to implement SET and RESET actions.

For readers who don't know what is a flip flop circuit, it is a type of circuit which retains the previous state of its output. For example , say if you have a flip flop circuit operating an LED. The ON and OFF conditions of the LED corresponds to the output state of the flip flop. If we switch ON the circuit, the LED lights up, of course. If we release it back, the LED remains ON. If we apply another press on the switch, the LED goes off. Again if we release the pressing, the LED remains off. This is what flip flop actually does. And due to this ability, it has an ability to store previous input without a need to retain the flow of current, which reduce power consumption and increase operational efficiency. This circuit is used extensively in computer memory and other types of machines that utilizes memory functions.

Here is the circuitry for flip flop using relays;

Update (19th Apr 2016): Unfortunately, Design B proposed above does not work (perhaps it will works at higher input power however higher input power will damage the LED. Updates on 21st Apr 2016: higher power also does not work!). Therefore a revision was made to Design B (see below), but at the expense of power loss since at this new design power is conducted at the triggering flip flop circuitry (Relay 1 and Relay 4) during ON state of the LED. Hopefully this new design will work (update will follow soon...)

Update (21st Apr 2016): Unfortunately, the amended Design B also does not work. I experimented for hours later on and found that the following design for single toggle works, but with oscillating output (LED is blinking). In order to slow down the oscillation, I added up a big capacitance capacitor across Relay 3 coil and the toggling eventually works, The higher the capacitance the slower the oscillation and the easier for you to toggle. Here is the schematic;

Update (22nd Apr 2016): I found a rather simpler circuit for toggling using relays here.
I have made some changes on the proposed circuit such as removing the resistor, introducing LED output and also using two SPDT relays instead of DPDT relays. I have tested and it works excellently, without oscillation. Here is my variant of the circuit.

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. 

Single transistor FM receiver (Part 2)

Hi, I m back after about 6 -7 months hiatus. Honestly, i was so busy back then due to my final year course here. The exam result will be coming out within a week and I will graduate a month later before returning to my homecountry.

As exam is over and I m now a free, jobless and unemployed in this summer holiday I manage to find some time to return to my delayed project, the FM receiver circuit.

My last post discussed about my generalised FM receiver circuit from lengthy hours of internet research. So far I failed to make an operable single transistor FM receiver although I strictly followed the circuits in the post. However it does not mean that the circuits are wrongly designed, since they were all proven to be operable by the designers who are very professional ( most of them are experienced electronic engineer and hobbyists). Thus I guessed the problems may lie within the component or my lack of hands-on skills, especially in the making of centre-tapped coil ( i m poor at soldering :( .... )

Due to that I continued researching from the internet. From some information gained, I readjusted the circuit without rigorous and analytical calculation (i m not electronic engineer though) but by intuitive manner, and try to avoid centre-tapped coil as possible as I can.

After several try-and-error, I managed to design an operable single transistor FM receiver. Although the signal obtained was quite faint for capacitor feedback than inductor coil feedback (will be mentioned below), its operability is enough to give me a little bit of joy as an amateur inventor. I managed to reach Absolute FM, one of the mainstream radio channel from FM bands in the UK and listen to some of songs I recognised. The signal can be improved by various means, however single transistor receiver is not really about quality (thats why it is not commercially manufactured) you designed it in order to learn the operating principles.

Sorry for not putting any video cuz I have no money to buy a camera, and my laptop webcam's microphone is not working very good to capture faint signal.

The following are the circuit I innovated;

The above circuit used small signal bipolar junction transistor 2N3904, one of the famous small signal transistor most commonly used for demodulation of FM signal (its even explained in Wikipedia). The values of capacitors, inductances and resistances are not strict, if yours are not working then just try changing the values. The RF choke can be used to suppress any high frequency signal from entering the audio amplifier, which is the main cause of unpleasant noise. The grounding must be properly done and the antenna must be long enough so the tune circuit current can flow properly and give out better reception.

The 5pF capacitor between the RF choke and the base of the transistor is the feedback capacitor. You can also use the same inductor as used in the tune circuit ( the 6-turn inductor) as feedback instead of capacitor, and placing both inductors close to each other to achieve resonant by magnetic coupling. I found that the signal was better by using inductors and magnetic coupling.

Another operable design I ve tried was by changing the transistor with JFET, an MPF102 transistor. In contrast with the above design, this time the feedback capacitor was connected to the source and the gate is grounded. However as the above design, the signal was better if using inductor feedback instead of capacitor.

In general the signal was faint and mono although perceivable by human ears. The quality of the sound is low, as expected. As I mentioned before, this type of FM receiver is not made for quality, but for learning purpose. To be honest I learned many things about feedback, FM demodulation and transistor actions from experimenting with this, and still learning. I believe that by learning the basics, then we can move on to improving quality.

Update: I just happened to know that my Iphone can record video. So I tried record the sound produced by the receiver, but unfortunately, the sound was not strong enough to be recorded and it needed high power amplifier to do that. Anyway, the circuit works and amplifier LM386 can gives loud output with earphone but not speaker, and the signal is not strong enough for recording unless amplified with high power amplifier.

Compared to this FM receiver, AM receiver (or crystal radio, as most hobbyist name it) gives loud audio signal, and LM386 audio amplifier suffices to enable this signal to be capture by using mere Iphone recorder. This may be due to the fact that frequency modulation is vulnerable to noise than amplitude modulation. Check out my video on crystal radio for evidence.

Single transistor FM radio receiver.

Here I will compile the products of my researches on single transistor FM radio receiver.

Generally when we think about FM radio receiver, what will be first to usually pop into our mind will be a complex kind of radio receiver, more than a diode and coil as usually utilised in AM radio receiver. In actuality its not the case when we take into consideration the original FM radio receiver invented by the FM radio transmitting pioneer Edwin Armstrong. He was credited with the invention of the first practical FM radio receiver, which use ONLY one non-linear electronic component ( the vacuum tube).

source:http://en.wikipedia.org/wiki/File:Regenerative_Receiver.png
The first FM radio receiver, using vacuum tube in regenerative topology.

With the invention of junction field-effect transistor, the vacuum tube was subsequently omitted from the circuit and being substituted by JFET. From my analysis on various FM receiver circuits found on internet I concluded a final generalised version of single transistor FM regenerative receiver as shown below:

FM radio receiver using just one JFET transistor as an active non linear element, in regenerative topology.

Most of single transistor FM radio receiver circuits I found on the internet dont deviate much from the above generalised design,except few which are completely different from it. But like I said, most of it follow the above configuration.

Now I am going to explain each part of the circuit, each numbered point below refers to corresponding red circled number in the diagram:

1) Group of capacitors: Some of the designs use capacitors arranged only parallely, while others just in series. Some omit the variable capacitors. So this part depends on the designer's choice. The value of the capacitors much be carefully chosen cuz it will determine the bandwidth within where the circuit will resonate. For FM receiver, the corresponding resonant frequency must be within 80 to 108 MHz.

2) The JFET transistor: From analysis I found out collections of transistor types suitable for the operation. Here are the examples: MPF102 (frequently used), BF245, J310 ( is now obsolete), 2N4416, RS2003 (Radio Shack JFET), 2N3819, BF256.

3) RF choke: The purpose of RF choke is to block high frequency signal from reaching the audio amplifier. It can be home-made, by just winding copper wire around a cylindrical air core or ferrite torroid. Various kinds of choke are made depending on the designers' choices.

4) Resistor: The value of the resistor can be adjusted to obtain the most clear audio output.

5) Capacitor: Same with resistor at (4)

6)Feedback capacitor: Its value is also designer's choice. This capacitor taps the coil at (7) to form a regenerative topology.

7) Capacitor's tap points: Part of the coil where the feedback capacitor touches. The position where the feedback capacitor taps is designer's choice.

8) Antenna and antenna's tap points: antenna touches the coil at the antenna's tap points. The length of the antenna, and the position of tap are the designer's choices.

9) Coil: the number of turns, the length and the diameter are all designer's choices.

10), 11) and 12) are capacitor and resistors to regulate the power supply. Their values are again, designers' choices.

By using this generalised circuit, anyone can play with various choice of values of any of the involved components, coils and transistors without being restricted to the designs proposed on the internet. It enables everyone to even create their own variants of FM single transistor receiver. To be honest, I ve tried various FM single transistor designs but none of them worked. And I m still trying hoping one day I will found a working one and this general design helps me alot in constructing various new variants.

Below I will show u several circuit designs made by several hobbyists, which I redrawn and omitted the audio amplifier part to enable easy matching with the general circuit proposed before.

Design 1: Philip Crane's design

Design choices (all numbered points refer to corresponding circled red numbers on the diagram):
2) JFET transistor: MPF102
3) RF choke: 26 turns, 30 AWG wire, 8mm diameter coil
4) resistor: 10kOhm
5) capacitor: 4.7nF
6) capacitor: 4.7-5pF
7) Tap: close to JFET's Drain
8) antenna's tap: 2 turns from power supply
9) coil: 22AWG wire 7 turns 2 inches long coil around 5/16" former
10) capacitor: 1nF
11) resistor: 1kOhm
12) 9V power supply

Design 2: Andrew Mitz's design

Design choices (all numbered points refer to corresponding circled red numbers on the diagram):
2) JFET transistor: 2N4416
3) RF choke: 22uHenry choke
4) resistor: 10kOhm
5) capacitor: 5nF
6) capacitor: 24pF
7) Tap: centre tap, soldered
8) antenna's tap: no antenna
9) coil: gauge unknown (assume 18AWG), 6 turns around 0.5inches diamter former, length 0.75 inches
10) capacitor: 1nF
11) resistor: 1kOhm
12) 9V power supply

Design 3: Andrew Mitz's design

Design choices (all numbered points refer to corresponding circled red numbers on the diagram):
2) JFET transistor: 2N4416
3) RF choke: 100uHenry choke
4) resistor: none
5) capacitor: 5nF
6) capacitor: 24pF
7) Tap: centre tap, soldered
8) antenna's tap: 3/4 of a turn from 10nF capacitor, antenna has 10pF capacitor on it as shown
9) coil: 18AWG wire, 12 turns around 3/8 inches diamter former, close winding (close wrap)
10) capacitor: 10nF
11) resistor: 1kOhm
12) 9V power supply

Design 4: Patrick Cambre's design

Design choices (all numbered points refer to corresponding circled red numbers on the diagram):
2) JFET transistor: MPF102
3) RF choke: 20 wraps of 24AWG around 5/16 inches former
4) resistor: 10kOhm
5) capacitor: 4.7nF
6) capacitor: each 5.6pF
7) Tap: tap closest to Drain of JFET
8) antenna's tap: Tap closest to power supply
9) coil: 22AWG wire, 8-10 turns around 5/6 inches diamter former
10)1nF capacitor 11) and 12) as shown

Design 5: Alan Yates's design

Design choices (all numbered points refer to corresponding circled red numbers on the diagram):
2) JFET transistor: J310 or MPF102
3) RF choke: 25uHenry choke
4) resistor: 10kOhm
5) capacitor: 6.8nF
6) capacitor: 10pF
7) Tap: centre tap
8) antenna's tap: no antenna
9) coil: 5 turns 7mm diameter and length (inductance about 120nHenries)
10) capacitor: 1nF
11) resistor: none
12) 9V power supply

Design 6: mikroElektronika's design

Design choices (all numbered points refer to corresponding circled red numbers on the diagram):
2) JFET transistor: BF256
3) RF choke: 22uHenry choke
4) resistor: 10kOhm to 22kOhm
5) capacitor: 6-100nF
6) capacitor: 22pF
7) Tap: centre tap, soldered
8) antenna's tap: closest to the Drain of JFET
9) coil: 5 turns 0f 0.9mm diameter wire (close wrap) 9mm diameter coil
10) capacitor: 1nF
11) resistor: 1kOhm
12) 9V power supply

Thats all from me. Hope this will help.

Cockroft-Walton voltage multiplier.

Cockroft-Walton voltage multiplier (CW multiplier) is another type of voltage multiplier that is widely used apart from Marx generator discussed before. It was initially used by scientists John Cockroft and Ernest Walton to perform atom splitting experiment, which earned them the Nobel Prize in Physics in 1951.

I built a simple battery-powered CW multiplier just to get 2mm spark, which enough to lit up a match or a cigarette lighter. As I ve explained long ago, the output from the 555 inverter must be amplified using LM386 before sending to the transformer to get such spark, but what if I didnt have LM386 but instead bunches of diodes and capacitors in my possession? Those diodes and capacitors are enough to substitute the role of LM386, by 'amplifying' the voltage as a CW voltage multiplier.

The function of CW multiplier is very simple. The fed alternating current from the transformer's output will go into the input of the CW multiplier. On first half of the cycle (first half wave), it will charge the first capacitor through the first diode. On second half wave, it will discharge the first capacitor thru the second capacitor and the second diode, so now the voltage stored at the second capacitor will be twice the first voltage stored at the first capacitor. By the end of the whole cycle, second capacitor holds twice the voltage of the supply while the first capacitor holds nothing. This operation is the first stage of the entire operation. Since I have 13 diodes-capacitors pairs, therefore I used about 6 and a half stages of multiplying.

But why the spark is so small ie 2mm length?? That is becuz the voltage generated from the transformer is very low. I measured it was about 180 to 200 V only, comparable to its original inverted operation which is to step down the mains voltage (240V) to about 2-3V ( the transformer is salvaged from battery charger, which was the one i ve been using before). By using CW multiplier, I got 2mm spark which was about 600 V. Though there are about six stages of multiplying I couldnt get six time the voltage from transformer due to diodes internal resistances. Anyway, this is worth experimenting so u know how much u will get by CW-multiplying voltage from a single 9V battery, using just a common battery charger transformer and a 555 inverter.

Below is the circuit I ve used:

Below are the photos taken:

The overall circuit.

The CW multiplier part. Note the white glue tape roller. It was made a former of the spark gap, where the 2mm spark will be observed.

Mains step down transformer salvaged from battery charger

The inverter part. I ve used the 555 inverter circuit.