001 Health and Safety

When I was sixteen, I began my apprenticeship as an avionics / instrument technician. The first thing we did was to attend a lecture on industrial safety, complete with scary movies of industrial accidents and a long list of 'thou shalt not' behaviour modes. This was before we'd even seen the workshop which would be our daytime 'home' for the next forty weeks.

It would be wrong of me to treat my readers any differently; safety first and always. This brief post will outline the essentials of radio experimenter's safety knowledge, but be aware that the author is not a H&S professional, and the reader is advised to take local expert advice before beginning work.

The potential hazards include:

Risk of burning. Soldering irons have a very hot functional end; the temperature is usually set to around 360 degrees C, but may be higher where an unregulated iron is used. Molten solder is at the same, high temperature, and because it is a liquid (and a heavy one), it can flow, drop or spray and cause burns.

Risk of cutting / abrasion / amputation. Some tools used have functional sharp edges; knives, hacksaws, chisels, etc. Always cut away from your body / hand / other parts. Take great care when cutting thin sheet materials; the edges will easily cut you.

Risk of puncture wounds. Some tools have functional sharp points, and care must be taken to avoid being stabbed by your own spike, needle, needle-nose pliers etc. Tightening a cable tie with pliers is particularly hazardous; the tie may break, and the pliers will move fast. Take care with cut wire ends. Larger wire sizes make sharp, stiff spikes.

Risk of poisoning. Some of the chemicals and materials used in electronics are dangerous. Do not open electronic components. Many contain susbstances hazardous to health, such as beryllia, polychlorinated biphenyls and lead alloys. Solder may contain lead in high proportion. Always wash your hands after handling solder.

Risk of respiratory irritation. Be very careful when cutting fibreglass panels; the dust is a respiratory irritant. Wear a dust mask, and if possible operate a vacuum cleaner by the work when cutting. Solder contains a resinous 'flux', which will vapourise when heated. Make sure you have adequate ventilation, and use a small fan if possible to draw the fumes away from you.

Risk of electrocution. Do not use mains power for your projects. The risks far outweigh the convenience; you can change a battery, but you only get one life. Make sure you electric-powered tools (including soldering iron and bench lamp) are in good condition, with no frayed or damaged wires. If in doubt, get a qualified electrician to inspect them.

Risk of radio-frequency burns. The projects, as published, do not produce enough power to cause significant danger of RF burns, but you should be aware that even modest RF energy can produce very painful and potentially dangerous burns on the skin.

This list is by no means exhaustive, and other safety information will be included in future articles as necessary.

I repeat once more - I'm not an expert - take advice if you are at all unsure. Work safe!

Basic Skills - Introduction

In support of the projects, I will be releasing some skill-related posts. These articles give the reader an introduction to each skill, and will also give links out to any resources the author finds during his research. The content is based on the author's own experience and learning, but there's a lot more to know.

The set begins as it should, with words of caution. Electronics assembly and experimentation is potentially hazardous, and the reader must make him / herself aware of these hazards. This first 'Health and Safety' post is by no means definitive. Safety information will be given occasionally as the topical need arises in future posts.

Take note that the author is not a Health and Safety professional, and whilst the advice given in this blog is given in good faith, the reader assumes all responsibility for his / her own safety. If in any doubt, take professional advice before undertaking any potentially hazardous operation.

List of forthcoming posts:
001 Health and Safety. Safety first, and always.
002 Hand tools. Outline of basic radio-construction hand tools. Other tools will be introduced and discussed topically, later in the series.
003 Basic fitting skills 01 - Hacksawing, filing, finishing. How to cut metal.
004 Basic fitting skills 02 - Drilling. How to make holes.
005 Basic fitting skills 03 - Tapping and threadcutting. How to make threads.
006 Electronic skills 01 - Cable preparation. How to strip cables and wires.
007 Electronic skills 02 - Soldered joints. How to make a joint, and solder it.
008 Electronic skills 03 - Wirewrapping. How to make joints without solder.
009 Electronic skills 04 - PCB making. How to make your own printed circuit boards.
010 Electronic skills 05 - PCB assembly. How to fit devices to a PCB.
011 Electronic skills 06 - Elementary panel wiring. How to wire-up electronic equipment.
012 Electronic skills 07 - Advanced panel wiring. Advanced techniques, including lacing.
013 Electronic skills 08 - Prototyping with stripboard. How to make projects using stripboard.
014 Electronic skills 09 - RF prototyping with copperclad. How to 'skywire' circuitry.
015 Electronic skills 10 - Basic circuit testing. How to make sure your project works.
016 Electronic skills 11 - Audio frequency testing. How to check for sound quality.
017 Electronic skills 12 - Radio frequency testing. How to check that new radio.
018 Light fabrication 01 - Sheet work. How to cut and fold cabinets.
019 Light fabrication 02 - Soldering. How to join sheet materials with solder.

There is no timeline here because these 'skills' posts will be interspersed with the regular Project posts. When a significant number are published, I'll add a sidebar navigation to allow easy access to both the skills and the projects.

Simple AF Amplifier

The Simple Audio Frequency (AF) Amplifier. An easy and useful introduction to home-build electronics, this project will take a low-level audio-frequency signal and boost it to 200 times its original strength. It has a level control to adjust the output for comfort, and will drive a pair of iPod / MP3 player headphones, or a small loudspeaker. It uses a 9V battery (PP3 / MN1604), and requires no setting-up or test equipment. To make it, you will need the following parts:

1. LM386 audio amplifier device
2. 10k logarithmic pot with switch
3. 1uF 16V electrolytic capacitor
4. 10uF 16V electrolytic capacitor
5. 100uF 16V electrolytic capacitor
6. Red 5mm LED
7. 1K-ohm resistor (1/8 watt)
8. 3.5mm stereo jack socket
9. 2-off 4mm banana sockets
10. Thin insulated wire (150mm)
11. PP3 battery clip
12. PP3 9V battery
13. 100x55mm single-sided copper-clad board

An experienced constructor would find most (or all) of this in their junk-box, but a newcomer to the art will need to buy these things new. I plan to market a kit of parts for this project, along with all those which will follow in the weeks and months ahead. Two big-name suppliers of components are Farnell ( http://uk.farnell.com/ ) and RS Components ( http://rswww.com ). Farnell may be the better bet for the non-corporate buyer, and they carry the stereo socket ( p/n 1280747 ), whilst RS do not. You will have to buy the sockets in multiples of five, as that is their packet quantity. No worries - you''l find uses for the other four in other projects and experiments. Another source of components is from old or broken equipment; see my article - http://www.lulu.com/content/e-book/component-harvesting/5327360 for more information.

You will of course need tools, and solder. Soon, I'll be adding teach-in articles (including videos) on tools and techniques; but for now, unless you already have the skills and tools, ask someone who knows how before attempting to make this project. Stick around! I'll tell you how it's done. I've spent over thirty years in the electronics industry, in several varied jobs, and I've picked-up a lot of knowledge and skills down the years. I intend to pass it all on to you.

The panel drilling is very straightforward. There are nine holes, and you'll need 3mm, 5mm, 6mm, 8mm and 10mm drill bits. Drill all holes initially with the 3mm bit; this makes it much easier to start the larger drills, and this first drilling size is called a 'pilot hole'. Make sure you clamp the panel when drilling. If the drill bit snatches the panel, it'll whip round and catch your hand. A G-clamp with a piece of wood to spread the load makes a good makeshift clamp. Clean the raised burr from around the hole edges with a larger-sized drill bit (hand-held), and then buff-up the copper surface with scouring pad ready for soldering.

Mount the sockets and pot first, locating them in their holes and carefully tightening their nuts. With care, a pair of snipe-nosed pliers may be used to tighten the nut of the stereo socket. Bend pins 3 and 4 of the LM386 up, and then outward, level with the top surface of the plastic case. These will be soldered to the panel as 'ground' connections. Turn the LM386 over. With the writing-side down, you have the remaining six pins sticking upright like a dead insect. Connection to these pins is now easy, and they are clear of the panel. Bend the 10uF capacitor's leads around as in the layout picture, and solder the capacitor to pins 1 and 8 of the LM386. These pins are at the 'notch' end of the device. Now add the remaining components. The red LED is pushed through the panel, and it's cathode lead is soldered directly to the panel. This is different to the circuit diagram; the diagram shows the resistor in between the cathode of the LED and the panel. It will work either way round; this is a good example of the flexibility which can be employed in electronics. Things aren't always this easy or straightforward, but I haven't the space now. I'll expand on this and much more, later.

Connect a PP3, a pair of headphones, and switch on. A buzzing will be heard in the headphones if the input socket is touched. What can you amplify? Try a magnetic (moving-coil) microphone, or an electric guitar. Search the web for 'crystal set' radio designs; the output can be amplified by this project. If you want to use a computer-type microphone (electret), it will need a power supply. This can be done by connecting a 47k resistor between the input socket and the switched side of the power switch. This will put around two volts on the microphone.

This simple circuit is simpler than normal for an LM386-based amplifier. I've left out three components; and these may be added if the amplifier is unstable or noisy. They will not normally be necessary, but you should be aware of them. A 100uF capacitor can be added between pin 6 of the LM386 and the panel, with the + of the cap to pin 6. This 'decouples' the power supply, stopping spurious signals getting into the device via the power supply. It also helps to stabilise the voltage, acting as a reservoir. Two other devices normally used in circuits of this nature are a 10-ohm resistor and a 100nF capacitor in series, connected from pin 5 (the output) and the panel. This 'Zobel network' helps to cancel-out the reactance of the speaker's coil, but if headphones are used the inductive reactance is too small to be of consequence. If you hear popping or howling when using a speaker, add the Zobel components.

Next week, I'll offer up some skills. There's a lot to learn, and the basics need covering first. When I was trained as a wirer, many years ago, we were instructed to wire-up panels fitted with tagstips and terminals, and the joints were made such that they held together mechanically. The units we made had to work before they were soldered. The wires had to be laid straight, and the stripping accurate. Any deviation from the rigorous standards, and the instructor pushed a screwdriver through the wire, and politely asked us to 'do it again!'. I'm not that overbearing; but I will teach you all I know about wiring, fitting and electronics assembly. Valves, Transistors, ICs, panel wiring, PCBs, wirewrapping, soldering, stripboard, the lot.

Theory will be added into the mix as required. I will not be teaching Maxwell's Laws of Electromagnetism, but I will tell you why you don't need them.

Cheap and Easy 4mm Connectors

An interim post; I felt it was worth sharing. I have used red bullet crimp connectors for some years as a cheap alternative to 4mm 'banana' plugs, which are used for test and measurement connections. Only the red ones work; the yellow and blue crimps are too big. Earlier today, I found it was easy to use the female crimps to make workmanlike sockets for use in test equipment.

All you need is a red female bullet crimp, and a pair of M8 nuts. It's simple. Use a nut to cut a shallow thread in the body of the crimp, and then use a pair of nuts to mount the crimp in the front panel of your new home-brewed meter, power supply, generator, whatever. I found it easier if the wire was already crimped into the terminal; the flattened, crimped section can be held with pliers while the nut is wound up the barrel of the crimp terminal.

For a really smart finish, you need a powerful soldering iron. A 100-Watt soldering iron has enough power to solder an M8 nut to a piece of FR4 copperclad. Drill an 8mm hole in the panel, lightly assemble a nut to the rear of the panel with a short bolt in the hole, and heat the nut. When it's hot enough, flow a little solder around the nut. Just add enough to give a 3mm 'fillet' joint. Wait until the nut has cooled before winding the crimp barrel into it; if you are tempted to do this in a hot nut, the crimp will shrink with the heat and drop out!

These crimp terminals are sold in motor factors, DIY stores and good, old-fashioned hardware shops. You'll find the M8 nuts in the same places. The connectors made in this way are fully compatible with 4mm banana plugs and sockets, and the tooling is cheap, too. Buy the simple pressed-steel cheap one you see in the photos; you can pay a lot more, but these work well enough for our purposes. Besides, you get a wire stripper, screw cutter and wire cutter in the tool as well.

Back to Basics

I've decided to start over. New ground rules for myself, and heaps of benefits for readers.

(1) I will post updates here regularly, every Thursday. If anything can't wait, it'll get posted, but the Thursday post is the routine.

(2) The amateur construction ebook will have its projects posted as news items here, with links to PDFs as they are completed. The project PDFs are free for anyone to download, anytime, anywhere. All I ask is that you download, and not link to them. 'Bandwidth thieves' will be dealt with.

That's it! Just a little more commitment and organisation this end. Enjoy.


So, starting over means back to square one? Yes, and it's real basic. The first project is a fundamentally useful one, and it has just ten components, including all connectors and the FR4 panel it's built on. I can't claim originality for this one; it's straight out of the data-sheet for the LM386 audio amplifier. Anyone with basic electronic tools can build this, and the parts will cost you around £3-50 total. If I were to present this as a kit, it'll cost you £7-50 including post and packing to UK mainland, battery not included. That's a thought I'm going to mull over.

The LM386 amplifier is available in a variety of sub-types; the only ones worth noting are the N-1 and N-4. The N-1 is the cheapest, and will deliver around 300mW. The maximum voltage is 12V, making it ideal for use with a 9V PP3 battery. For higher voltages and more power, the LM386N-4 can use up to 18V and supply 1000mW (a whole watt) of audio power, great for small speakers. Its Farnell code is 1184987, and they sell it for 57p.
Next post here will include links to this first project, and give an overview of the next. I'll also include links to things I've discovered while researching 'out there', a practice harking back to the original purpose of blogging; a list of links and commentaries on websites.

Diversion into sales

I'm letting the new radio percolate for a few days, while I sort out some sale stock for my eBay account. I've built up a significant amount of surplus over the years, and I'm disposing of some of it to make room, and funds, for the kits project. I'll be releasing the stuff onto the lists over the weekend, and I'll update here with links and information on the items available.

Another thread of the business is the information products. I'll be unable to commit any serious time to this for the next few weeks, as the hardware sales will take precedence. The only new information likely to be published will be for the kits!

Early Development Prototype - CW84

I'm calling it the CW84 because it's a refinement of an 80-metre cw transceiver I made about four years ago, which I called the CW80. Not only is it four years younger, but the true wavelength of a 3.550MHz signal is 84 metres. It's a direct-conversion receiver, very straightforward in design, with an equally simple transmitter tacked onto it. A 700Hz offset is added to the transmitted signal by adjusting the control voltage fed to the tuning varactor, which is a forward-biassed LED.

Today, I achieved some satisfactory results with an initial development prototype. It's cobbled together on stripboard, and the picture shows the diagram of the circuit as it stands. There is as yet no RF input to the SA602 mixer / oscillator, and I haven't tried to recover any audio from the thing. It does, however, tune it's oscillator sweetly between 3.550 and 3.583MHz, which is exactly the 30kHz I wanted; this little band covers the 3.555 and 3.564 slow Morse code (QRS) 'sandpits', and the 3.560 low-power (QRP) centre of activity.

The front end may be a simple bandpass filter and a 1k-ohm pot attenuator, or I may include a FET preamp as I did in the CW80. I'll try to avoid complexity wherever possible. The whole idea is one of simplicity; very little setup, few wound components and even fewer trimmer capacitors. Today, I eliminated a padder from the oscillator tuning, and that's the kind of change which I welcome. There will be no AF gain pot. The original CW80 doesn't use one, simply because the RF attenuator does all the gain-setting required. It also stops a novice operator from setting the RF gain too high, backing off the AF gain and wondering why the mixer is getting swamped with powerful signals. The SA602 is a lovely device, if you respect the fact that Gilbert cell mixers are easily overloaded, but have good conversion gain and hence work well at low input levels. Another simplification is in the AF output stage. The LM386 is noted for its low ancillary component count, but I've taken the liberty of doing without the bypass on pin 7 and the Zobel network on the output at pin 5. If they prove necessary, I'll add them; but only if.

Tomorrow (hopefully), I'll add a front end and a pair of 'phones. I may even try listening to my gate-dip oscillator later tonight. Whatever happens, and whenever I get around to doing it, I'll post it right here. Remember; as always, although I assert copyright on my work, please feel free to try these things for yourself. I intend to market kits for these projects, and support them with this blog and other web-based materials, but use your junk-box stock or the shopping-lists which I publish with the designs.

Witlessness and woe

If I've learned anything this evening, it's how to waste three hours work on one simple detail. The new radio was laid out three nights ago, and it looked elegant, compact and concise in its prototype stripboard form. The resonators, 1K pots and 100p COG capacitors arrived today, so it all looked good for a first build. Thursday evenings are free of Sea Cadet obligations, and nothing was planned by the family. I settled down in my untidy position at my desk in the extension, and carefully loaded the stripboard. My youngest son came by to wish me goodnight at around 2100, and I was just hooking-up the tuning pot. The tuning LED glowed and dimmed, the volts were where they were meant to be, but no output from the SA602. I'd put a 100p cap on pin 7 (the oscillator emitter), to take the signal to a keyed buffer for the transmitter. I was patiently listening with my old Realistic DX-392, looking for signs of life. I searched the board for open joints, solder whiskers, anything. I changed the ceramic resonator for another type, I removed the bandsetting padder, I changed the LED coupling capacitor, nothing.

Then it hit me, like a huge, soggy mattress. I am so used to using chips upside-down on a piece of copperclad, that I'd laid the board out with the two chips back to front. The entire layout is scrap, and I face a fresh piece of quadrille paper to start afresh. Ho-hum.

It's wonderful to watch your ideas take shape, and weird to watch the shape change as the ideas mature into workable products. The latest radio is no exception. I went through a panic stage four days ago, and the direct-conversion receiver / cw rig turned into a Pixie II, and back again. Do a search for the Pixie II, it's a fascinating exercise in minimalism. The PA transistor doubles as the receive mixer; keying the PA emitter shorts the receive path and puts the transistor into full drive. On key-up, recovered audio is passed to an LM386, and into a pair of 32-ohm headphones. Usual power source is a 9V PP3, and the housing can be anything from an Altoids tin to al fresco.

I did say it turned back again, and it remains a variant of the Rev. George Dobbs G3RJV's famous 'Sudden' receiver. I'm using Micrometals iron toroids in the receive preselector, and a 3.58MHz ceramic resonator as the frequency controlling element. I need tighter control than George's VFO original, because it's also transmitting. I've settled (for the time being) on a 30kHz band, from 3.55 to 3.58. This includes the QRS 'sandpit' at 3.555 and the QRP centre of activity at 3.560. The radio has a 700Hz transmit offset, given by arranging for a pair of resistors to be switched in and out of the frequency control voltage 'totem-pole', which feeds the LED varactor. Not only am I using a LED as a varactor, but I find that forward bias gives more linearity. This method is not original, but has been used with success in the radio home-brewing world for some years. The other feature of the forward bias is that the LED can be brought out to the front panel, adding interest as the radio is tuned. The LED dims and brightens, glowing well at the lowest frequency.

I'm currently waiting for parts, and I have two evenings ahead of me where I'm committed elsewhere, so it'll be just ideas until the latter part of the next weekend. With a following wind, the prototype may be running inside a week, and taking reports from Southern England. We'll see.