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.

Single-transistor flyback drivers.

keywords: single transistor flyback driver, single MOSFET flyback driver, simple flyback driver, one transistor flyback driver.

So far, i have dealt with several powerful flyback drivers such as ZVS and 555 timer. To be honest i m more interested in a simpler but powerful flyback driver, so i researched about drivers that utilise only one transistor.

The most popular one-transistor flyback driver is one that uses the ubiquitous 2N3055 NPN silicon power transistor. The schematic is as shown below. The number of turns of the primary is not critical but generally the trickler coil ( the one connected to the Base of the transistor) is having lower number of turns than that connected to the transistor's Collector.

My own variant of the circuit. This topology is also known as Armstrong oscillator, due to Edwin Armstrong who invented and applied this topology for his regenerative FM radio receiver. To recognise this topology is very easy; it has two coils, one having more turns than the other, and it has only one transistor ( or traditionally, a vacuum tube).

Surprisingly, when I substituted the transistor with MOSFET, the circuit is still working. I substituted the Collector, Base and Emitter of the transistor with the Drain, Gate and Source of the MOSFET, respectively. IRF840 and IRFP250N worked successfully, but it didnt work with IRFP450 ( dont know why, if u know why then u can teach me in the comment section). Below is the same circuit, but using MOSFET as an active component.

For both circuits, I found out that my laptop power supply that I m always been using ( 12 V, 3.16 A) cannot be used anymore for these circuits, since it baked the transistors and MOSFETs and if not, degraded them significantly, even though i ve used zener diodes at the base or gate of the devices. I inferred that might be due to large current (3.16 A) of the supply. Therefore I resorted to simpler supply which is the common 9V square battery. Both circuits produced less powerful arc than ZVS or 555 driver ( maybe due to lower power when using battery), and the arc was about 0.5 to 1 cm length. The winding direction of the trickler coils of both circuits can be reversed, and it still works successfully. I know that the circuit can be further improved so that it can fit larger power supply, but my superficial electronic knowledge and tight budget ( i am poor student, T_T) limit improvements and haunt me of more transistor burnings (so far I ve burnt between ten to twenty MOSFETs during three months of experimenting, and each of them worth 1pound. So count by yourself how much lost i ve been facing!). I really hope someone can tell me how the circuits above can be improved for larger power supply. :D

Below is the circuit that didnt work EVEN when using the battery power supply ( I think this circuit actually didnt work, it just damages your MOSFETs and BJT). I just posted it here cuz I am perplexed with most designs of Armstrong oscillator that utilises the following configuration. I dont know the reason behind that, but it seems that most of the designs are using higher power supply. (such as 50, 100 to 140 W, while the highest power supply i have which is the laptop power suppy is just 40 W, in fact, always lower than that!) I also hope that someone experts can explain why the following circuit didnt work.

This circuit doesnt work even when using 2N3055 transistor.

Marx generator.

Marx generator is a voltage multiplier that multiply the high voltage direct current to a higher voltage level, by charging a group of capacitors in parallel, and discharging them in series.

I built a Marx generator with original intention to increase input power into my Tesla coil, but didnt working. However its still working as a Marx generator itself, so still worth mentioning in this blog. :P

The operation of Marx generator can be best understood by studying the diagram, retrieved from Wikipedia:

My version of Marx generator has no major difference from any other versions. i used three-stage multiplying, using three 2-litre bottle saltwater capacitors wrapped in aluminium foil as plates. Each of the capacitors was measured to be 5nF in capacitance. There are three spark gaps, where two are small spark gaps as switches and a final spark gap. I ve made the final spark gap larger than the other two, and connecting it directly to ground instead to a voltage divider and load ( as depicted in the above diagram).

For the spark gaps, I have two small spark gaps each of 1.5mm gap length ( it varies around that value cuz u need to synchronise it to get best length in order to avoid corona discharge, cuz corona discharge between the gap may spoil the operation). The spark gap was made by screwing two metal screw into a circular former, either by using glue tape roller, or plastic bottle caps. I used screw to enable easy synchronisation of the gap length during operation.

All the resistors are at 1 megOhm each. The final(big) spark gap was also constructed similar to other two spark gaps. Initially i set the final spark gap length to be 0.5cm, and increased it gradually to get the maximum spark length that can be obtained from the overall configuration of the Marx generator. The maximum spark length observed is about 1.5cm. Yes, its too short for most hobbyists, due to small number of stages ive been using. I am intending on buying more high voltage capacitors to reduce size ( saltwater capacitors are too big and heavy) and make the overall design compact and smaller ( and portable as well) as well as increasing the number of stages to maybe 20 to 30 stages. I wonder how long the spark i will get...

Here is the schematic of the marx generator built:

Here are the photos taken:

The overall setup. Ignore everything outside the A4 papers boundary. Just focus the interior. The noticeable three big bottles are my saltwater capacitors of 5nF capacitance each. I m using my ZVS power oscillator (but changed the 1N4007 diode to BYV26E, IRF840 transistor to IRFP250N, and 10nF capacitor to high voltage rating 1uF capacitor for faster switching, cooler mosfet and higher efficiency and power) fed the oscillating power into the flyback transformer. The transformer rectified the oscillating current in it so there is no need to use diode. The high voltage direct current is then fed into my Marx generator.

Closer view.

Power supply ( laptop power supply, 12V,3.16A as always used before) which is the black wire with yellow wire at its end, breadboard populated with components in ZVS oscillator confg, and a flyback transformer ( the only chunky thing close to the breadboard)

Capacitors and small spark gaps bird eye's view.

Closer look on the small spark gaps. The white one was not used, so i closed the gap.

The small spark gap using screws and plastic bottle cap.

Another small spark gap, also using screws and plastic bottle cap.

As mentioned before, this small spark gap is not used, so i closed the gap. This was constructed cuz i though another small spark gap would be necessary before the final big spark gap, but when finding out it wasnt important later on I just leave it there by closing it. This gap was constructed with glue tape former and two screws.

This is the final and the biggest spark gap where the final product of the Marx generator ( the longest spark) will be observed. It was constructed similar to the unused small spark gap. Just ignore the red tape former over it cuz it is just to hold the wires carrying voltage to the final spark gap in place.

Final (big) spark gap.

Here is the video. I have to put on a video this time cuz it was really hard to capture a photo of a flashing spark. Enjoy it!

Tesla coil; resonance demonstration.

Today i ve nothing new project to post except to just wanna explain my recent demonstration of resonance and wireless energy transfer using mini Tesla coil i ve built recently.

Resonance is the very fundamental concept that enables the functions of most current ubiquitous wireless devices. Radio receiver, handset, radar,satellite and televisions are all dependent on this principle.

Resonance occurs when the frequency of the energy supplied to a system is the same as the natural frequency of the system. At resonance, the system will receive most energy from the energy source, and tend to damage itself, unless controlled.

In Tesla coil, like no other conventional transformers, the secondary coil resonates with the primary coil. Hence, most of the energy supplied by the primary coil will be intercepted by the secondary coil and this in turn increases efficiency. To achieve this, of course (by the definition of resonance) the natural frequency of the tank circuit formed by the capacitor and the primary must be the same with the tank circuit formed by the air-earth 'capacitor' and the secondary. Since the secondary coil tends to damage itself with excessive energy being transferred into it, therefore a spark gap is made at the primary coil to release the excess energy.

Since resonance occurs at the same frequency of energy source and receiving system, i wondered whether the energy received by the secondary coil can be transferred further to a similar system with same or almost same natural frequency. Due to this, i constructed a third coil , which is having same diameter, length, wire diameter in order to make its natural frequency as close as possible to that of the secondary coil. The following diagram shows the secondary coil and the third coil.

Both coils, secondary and third coils.

Current setup. Its the same i ve been using before. The 275ml bottle wrapped in aluminium foil is my homemade capacitor. I chose this one cuz it gives longest spark on the secondary ie it enables the primary ( the yellow wire) to resonate with the secondary.

The system, without the third coil. A strand of corona was pulled by using screwdriver. Its about 1.5cm length.

When putting the third coil in the vicinity of the secondary coil, it resonates and due to this, a 0.7cm can be observed between the screwdriver and the breakout point. How do i prove that it really resonates and not receiving energy from the yellow wire ( the primary coil)? I removed the secondary winding away, and then tried powering the circuit again. And no spark was observed at the third coil. This proves that it really resonates with the secondary coil.

How the resonance is applied in telecommunication? Well, i guess u can contemplate over the experiment. The secondary is the transmitter of the energy while the third coil is your 'handset', television, radio receiver and any type of wireless devices. The differences between resonance observed in my demonstration and the resonance in real application in wireless devices are that the power is transferred at larger distance and higher band of frequencies, and the power is not only bringing itself, it also brings signals ( it is modulated )that will be translated and amplified into perceivable video and audio signals.