Saturday, 24 November 2012

Wind-up Torch, what a Wind-up!

Don't get me wrong, this really isn't important, but I have to say it did make me chuckle at the sheer irony and cheek!

Some time ago, and I can't for the life of me remember when, and it doesn't matter anyway, I bought a "Wind-up Torch" from a supermarket chain - ASDA  I think, though I certainly wouldn't swear to it.

Frankly I was never very impressed with the performance of it from the day I bought it.

As I understand it, with a wind-up torch, one was supposed to crank the handle like billy-o and then one would have a usable torch for a while afterwards.

Well this thing I bought was never any good, any light after the cranking was short-lived, and if one wanted a steady light, one just had to keep on cranking steadily away which kind of defeated the object.

Anyway, as it was very cheap I never really got "wound up" (sorry!) about the problem, and kind of put it down to experience, as one does.

Anyhow, the day came when the thing finally refused to work AT ALL, and I decided to dispose of it, but being one who gets a bit of a kick out of recycling electronic components in home brew projects, I decided to disassemble it before I disposed of the the remainder.  So out came the jewellers' screwdriver set.

Very soon after starting the dismantling process I spotted something rather odd - a lithium battery.

Why did my wind-up torch have a battery in it, and, frankly, not much else?

The attached photos show what I found :- a small "generator unit", a pcb with a lithium battery, some diodes, one small SMD capactor, a switch and three LEDs.

As soon as I saw this little collection, I smelled a rat!   Surely, I am going to find that the battery is flat (thus explaining the lack of light), I thought.  Guess what?   Flat as a pancake!  No surprise there . . .

I shall leave it to the reader to work out what can be done with :-

(a) a small electromechanical hand-cranked generator

(b) a dpco switch

(c) about half a dozen small rectifier diodes

(d) a 100nF capacitor

(e) Three white LEDs

(f) A coin (lithium) cell

(g) some small reduction gears  . . .

Wednesday, 28 March 2012

Electronic Experimentation (Spiralling Off . . .)

I wish now to relate something of the pleasure which can be experienced whilst carrying out simple experiments.

The Nutty Professor is at it again ! ! !

As many who experiment with home construction would no doubt relate, one thing quite often leads to another, which in turn leads to another, and so on (or to misquote a line from the "Commitments" movie - they go "spiralling off").

It's a wonderful thing on the whole, but one of the frustrations with it is that one never seems to get anything quite finished!

Readers of earlier blog entries will have spotted references to crystal controlled transmitters and receivers for use with the QRSS aspect of the amateur radio hobby.

Successful (one hesitates to say "the best" as this implies some sort of competition, and I don't think QRSS folk are particularly competitive) QRSS stations, whether simple or complex have to be well engineered.

Sloppy engineering practice soon becomes evident, manifesting itself in unreliability or in poor performance, and the poor performance I am thinking of in particular is that of frequency stability, or rather the lack of it.

My own home made efforts have exhibited acceptable, if not outstanding stability, and one quickly looks to ways of improving performance.

For some time now I have been pondering this issue, and a chance visit to a rather interesting web site produced a nicely written article explaining how to make a simple crystal heater
Thermostatic control of the temperature of the crystal used to produce the QRSS signal, or local oscillator in the case of a receiver seems to be a fairly obvious thing to do, and I had already looked at a commercial offering which offers high stability for a few pounds, and is a microcontroller based solution.

The heater to which I am referring though is a much simpler affair using a darlington transistor to modulate the flow of current through some low value resistors (the heating elements), with a thermistor to provide regulation and feedback.

This struck me as a brilliantly simple idea, so I resolved to build something similar if not quite identical.

With the exception of the thermistor, all parts came out of my junk box, in fact the darlington transistor was concocted from a small power transistor rescued from some long-forgotten project (the leads had been cut and had traces of old solder on them) and a low power Japanese 2SC something-or-other freshly removed from a scrap board which was probably a transistor radio or portable TV 20-odd years ago. Total cost of parts, probably quite a bit less than a pound.

The crystal being thermally controlled (heated) is physically but not electrically connected to a heated piece of thin tinplate (formerly part of a screening can also rescued from a scrap board).

When connected up to a power supply, my little heater worked first time (it is so simple it could hardly fail), and after some experimentation with the settings I had it heated up to just under 40 deg C, and was able to adjust the crystal FREQUENCY (the crystal was electrically connected to a completely separate test oscillator) by tweaking the temperature of the heater. The heater once it reached equilibrium maintained its set temperature perfectly.

My test set up involved monitoring the current drawn by the circuit, and the collector voltage of the transistor.

Pretty it ain't - interesting it certainly is!
Inspection of the circuit shows that they go in opposite directions - when the collector is high, the current drawn (and therefore the power being dissipated in the heater resistors) is low, and vice versa. If the surroundings change, or the circuit is heated up or cooled down deliberately the circuitry compensates for the changes very quickly thus restoring equilibrium.

One quickly realises that this little heater is really trying in its own small way to regulate the temperature of the
whole planet, and for it to be as economical as possible, it needs to be thermally insulated as much as possible from the outside world, and a little more thought reveals that in a way this little circuit is a miniature representation of, say, a domestic dwelling where the occupants try to maintain a comfortable temperature inside when the weather may be up to all sorts of tricks on the outside.
The heater schematic


Also, as I have an interest in the application of microcontrollers, this application is also, as stated above, one where a microcontroller could be used, but this is where one needs to think about cost. Even buying new components, the unit cost of my little device would be no more than a pound, and the cheapest microcontrollers cost in the region of 75 pence per unit, so by the time you've bolted any additional components required, the simple version probably wins out, but only just. Die hard microcontroller enthusiasts would probably dispute that assertion!
Either way the mere consideration of one approach versus the other illustrates perfectly how experimentation can lead one through all sorts of interesting thought processes, which is really the whole point of me writing this note.

Saturday, 25 February 2012

The Mad Mad World of Microcontrollers

It's been a while since my last blog, and that has been bugging me to the point where I feel I have to "tick the box" and "blog SOMETHING", so here it is.

The last entry was made shortly after I'd "discovered" the Arduino system, and this discovery has let me spiralling off into all sorts of strange directions, all associated with microcontrollers, one way or another.

In the meantime I've bought what I think is a rather good book called "The Quintessential PIC Microcontroller" by Sid Katzen which deals with the subject manner in a way which resonates with the way I approach things.   Recommending books is a dangerous business, rather like recommending restaurants or wines or other things which are extremely subjective in nature, so all I will say is that I think it's rather good and leave it at that.

I've also acquired a few bits and bobs associated with Atmel AVR microcontrollers (an Atmel AVR is at the heart of the Arduino), namely a "TinyUSB" programmer, a few low-end microcontrollers, an LCD panel, and I've just downloaded the AVR Studio IDE package from the Atmel web site.

Buying expensive text books apart (I only have a couple of microcontroller books, honestly!) the best way to "learn microcontroller" is by doing stuff, so that has now become the prime objective.

I should relate the story where my eyes were opened about the desirability of using microcontrollers.  This was when I was participating in a Radio Club project to scratchbuild a 70MHz transceiver (The Eden 9 Project) and had got to the point where working IF strips were emerging from our group of constructors.

The IF strip had been deliberately designed without an AGC system, but with the facility to add AGC later, and a prototype audio-derived AGC system was duly demonstrate.

Now some people are rather "sniffy" about audio-derived AGC - I may or may not have been one such sceptic, I couldn't possibly comment! - but this demonstration was remarkable!   Not only was the performance of the circuit so impressive, but the parts count (and cost) was so low!  

Of course, as I am sure you have worked out already, there was a PIC microcontroller at the heart of this little add-on board, and when one stops to consider how the "all analogue" alternative might have been designed then it doesn't take long to realise that the alternative would be more complex, costly and less flexible.   With a microcontroller prototype, just changing a few numbers inside the embedded program is the way performance is tweaked.  To cap it all the PIC at the heart of this unit retails at around a pound at time. Good value, or what?

All I need now is the time, willpower and inspiration to get down and learn the ropes properly.

Sunday, 22 January 2012

New Year, New Ideas (or not!)

I don't think I am capable of "Original Thought".

Every time I think I have discovered something new, I realise that I am re-inventing the wheel.

Please don't think I am bitter about this, if I have a philosophy in life it would be a misquote (no blasphemy intended!) of one of the "Ten Commandments" (or to be more specific the Tenth Commandment) in that I do not (or at least try very hard not to) covet what another has.

Wives, possessions, original ideas, it's all the same thing to me!  Coveting like resistance (misquoting the Borg this time) is futile.

A couple of weeks ago, a professional colleague who works at our Head Office, unlike me who works "out in the field" mentioned something called an "Arduino" to me, and I had to confess that I'd never heard of it.

Anyway, to cut a long story short I looked "Arduino" up on the web, got very excited (!) at what I saw, bought one, faffed about with it and began asking friends and other colleagues if they knew about this wonderful piece of gadgetry, and it seems that I was the only one who thought it was something "new"!

Largely thanks to my friend and mentor, Ron Taylor (G4GXO) of Cumbria Designs, I had been introduced to the world of microcontrollers some little time ago, in connection with the "Eden 9" project.  For those who don't know, the Arduino is essentially a "mini microcontroller development board" based around an Atmel microcontroller, and as such could be described as a "microcontroller on steroids".

Further research, and reading of other bloggers' output revealed that Arduino isn't the only contender in this market place, Julian,  G4ILO has blogged about the "Gadget Gangster Propeller USB" platform, which seems, at least to the casual observer to be more or less the same thing but done with different hardware.

The unfortunate thing for me is that I now have ANOTHER interest to compete for my limited free time with QRSS, meteor observations, Digimodes, Classic Rigs, etc etc.   If only I could afford to retire from the Day Job and play with all these new toys!