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.

TS-180S Display Fixed (Again!)

As I reported previously I discovered that the display in my TS-180S which is currently undergoing major restoration was again faulty.

The symptoms were either that it displayed just the "base" frequency of the band in use when it was powered up, "1.500.0" for example on Top Band, "3.500.0" on 80m, or another sequence of numbers unrelated to anything.  None of these numbers changed when the bandswitch was operated with the set switched on.

A couple of nights ago I decided to have a look with my test gear to find out what was going on, or not.

The trickiest part of the whole operation is extracting the display from the radio, and conversely refitting it after investigation, and this struggle led me to suppose before I started that the fault was induced during the arduous refitting after the previous repair, and the consequential tidying up of the cable harness.

This was soon proved not to be the case as investigation with an oscilloscope quickly led me to the conclusion that (a) there was plenty of 40-40.5 MHz signal from the premix unit but (b) there was no gate signal in the digital counting chain.

So attention returned to the previously repaired divide unit which sits underneath the main counter board, and so consequently the whole caboodle had to be extracted once again from the radio so I could get at it.

Well at least I was well practiced at this, and knew what to do (familiarity doesn't imply enjoyment!), so eventually, after cutting some of my nicely installed cable ties, and much cussing, I had the recalcitrant unit upended so I could investigate.

TS-180S Display Divide Unit

The marked up drawing above shows what I found, and I quickly came to the conclusion that either Q8 or Q9 would appear to be faulty, with the balance of probabilities suggesting Q8.

 

Fortunately a trawl through my spare parts revealed that I had a 4013 (Dual D-Type Flip-Flop) and also a 7400 if required, so I had a "cunning plan" to replace these parts in the radio the following evening.

 

 

 

 

Divider Board - Q8 Bottom Right

 

And so it came to pass.  The following evening Q8 came out as sweet as a nut (it was helpful that it was in the corner of the board and no immediately surrounding components, a new 14-pin turned pin socket was soldered in and the new chip installed.

 

Powering up the radio followed and to my great delight the correct frequency display appeared!  Yay!

 

Display Correct (note - upside down!)



Display ready to go back in ...



The display has now been refitted and is working as I type this, so after much effort, I am now back where I started and wondering (a) what on earth will go wrong next? and (b) how can one radio have had so many seemingly unrelated faults?    The only connection I can think of between this fault and the previous repair to the divide unit is that both of the faulty chips were CMOS types of presumably similar vintage?  Maybe the anti-static handling precautions at the factory weren't up to much at the time?

 



Faulty Q8 - Innocent Looking, eh?



 

First Swallow of the Summer, etc

THIRTY-odd years ago, early in my professional career I moved up to Central Scotland from Yorkshire, where I remained for about six years.   In the late Spring of the first year I was there I noted the date on which I spotted the first swallow of the summer, it happened to be May 1st, and thereafter May 1st has been the "yardstick" with me for spotting these harbingers of the coming Summer.  For some reason I'd never taken any notice of this phenomenon before.

Having subsequently back to South of the Border, some hundred miles to the south, I usually reckon to see swallows two or three days before that particular date, but unusually this year, it is now April 30th, and no swallows have yet come to my attention (I am not saying they aren't hereabouts!). However, unusually this morning the first house martins I've seen were swooping around the front of my QTH.  Usually swallows are to be seen before the martins in my experience.

TS-180S Repair - Part 2

It is now time to report on the progress with my ailing TS-180S.   Until yesterday evening there wasn't much to report save that I had come to a couple of conclusions.

Firstly, the radio definitely has a problem with the PLL circuitry.   That's enough to make one feel that this could be a long haul!   PLL circuits can be difficult to diagnose and fix, as they only work when the loop is closed, and a fault anywhere in that loop could potentially stop the PLL from working.  This radio has a quite early implementation of the "PLL derived PreMix System" which became popular in era immediately prior to the adoption of full synthesis and continuous coverage.  Trio improved the circuitry for their very popular TS-120 model, but I am left to struggle with their earlier attempt.  The PLL circuitry doesn't lock very well, and when it does lock, for a 100kHz change in VFO frequency, the actual het. frequency derived in the PLL Premix system only changes by 60kHz.

The TS-180S PLL Board

 The second conclusion I came to after probing around the circuitry with a spectrum analyser was that the high gain Wide Band Amplifier between the VCO stages and the prescaler/divider was producing a lot of garbage.

I'd previously checked out the condition of the two electrolytic capacitors in this part of the board on my ESR tester, and they suprisingly appeared to be absolutely fine.

With this knowledge I began to ponder how I might break into the loop and possibly inject test signals from a stable source, (ie replace the WBA with a signal generator and see how things behave), but before doing that I decided I would check the DC conditions around the five transistor WBA.   These checks showed that the first transistor in the chain (Q14) appeared to be short circuit in all directions.  Hah!  That is clearly not going to help!

The 8-40MHz Wide Band Amplifier - things are just a bit tight in there!

Anyhow, the faulty transistor was extracted with no little difficulty, tested, and yes, it is completely dud.

Unfortunately I don't appear to have anything close to it in my spares, so it will have to be an EBay search for something suitable.   The original transistor type is 2SC1907 which has a very high fT (>1GHz), so any old gash BC182 just won't cut it on this occasion!  According to the data sheet the 2SC1907 was designed for UHF TV local oscillator applications.

To be continued ...

A "Doing" Day (in the shed)

A few days ago a Skype message from one of my small group of "Skypees" alerted me to the fact that an equipment failure had occurred. Jim's 30 amp power supply was no more. I was being asked what I thought about a couple of possible replacements, but as I enjoy the challenge of "fixing things", and also generally far too parsimonious to countenance replacing something old with something new without at least putting up a fight, the Skype conversation quickly got round to the faulty equipment and to what might be wrong with it.

With almost astonishing speed I was appraised of fault symptoms and then a copy of the circuit diagram. It was completely dead. Nothing coming out of it, apparently. Nil. Zip. Nada. Not even "magic smoke".

The circuit diagram was examined and I figured out some likely causes, all which seemed to be fairly straightforward to resolve, and so it was arranged that I would call in to see my friend when I was passing his home a few days later.

In the meantime, my friend proceeded to purchase a replacement unit (a hundred pounds, near as dammit!) and was very pleased with it.

The broken power supply was duly collected yesterday afternoon, and today I decided to take a look at it.

The power supply is called a "Nissei DPS-300GL" and is quite a hefty beast. Opening it up I found it to be quite nicely constructed, albeit rather grubby as the cooling fan had been dragging unfiltered air in and across the internal heatsink for many an hour. However, no matter what the outcome of my efforts was, the fan would drag no more air as it was completely seized up beyond redemption.

Inside the Nissei PSU (quite neat isn't it?)

My earlier deliberations had led me to suspect a problem with the overvoltage circuit, but I adopted a technique I have used on many occasions to prove or otherwise the general health of power supplies, and that was to connect a current limited supply at the correct DC voltage across the main rectifier output. Encouragingly this brought the majority of the power supply to life, at the same time lending weight to my original theory about the overvoltage tripping circuit which was fed from a completely separate supply via its own transformer.

Next I moved the external supply to the rectifier in the overvoltage circuit, and to my slight surprise the "enabling" relay (the overvoltage trip drops out the relay which removes the AC mains supply to the main power supply transformer) was heard to operate. My original theory was that there was a fault with this relay, or its associated driving circuitry.

Fortunately this piece of circuitry is built on its own separate board and was relatively easy to extract and examine.

It didn't take long with an eye-glass and a multimeter to get to the root cause of the problem - see the attached photograph.

Underneath the Overvoltage Board ...

A nasty looking joint at the relay contact which switches the AC mains to the main part of the power supply. Bingo!

The joint was cleaned up and resoldered, the overvoltage circuit returned to its rightful place, the PSU powered up from its own mains supply, and lo and behold the PSU is now working, albeit temporarily without a cooling fan.   I realised at this point that the description of the original fault symptoms must have been slightly wrong in that the trip relay would have been heard to operate upon the application of mains, and I didn't verify this myself. Having said that this might have made me more worried about what the cause of the fault was!

Having spent a few frustrating minutes wrestling with Maplin's web site looking for a replacement,  EBay was consulted, and a 92mm 12V DC fan was quickly found and has been ordered for the princely sum of £4.99 (including postage!).

Soon Jim will have a spare power supply.

Right!  On with the next job ...

Today is the day I finally decided to start building my "X-lock", a VFO stabiliser kit from local firm Cumbria Designs.   I've had this "in stash" for quite a while as other projects have got in the way.  Once built I have then to decide which rig of my various"old ladies" will get the benefit.  At the time of writing I think it will be my FT-107, but that is by no means certain.   I also have it in the back of my mind to build the version described by Eamon Skelton EI9GQ which seems to be a variation upon the same theme.   Still, that will be a way off as I still have to "cut my teeth" properly with PIC programming, another medium-term objective of mine.  It will be interesting comparing the performance of the two units, and the advantage of the EI9GQ version is that the PIC source code is in the public domain, and I would have the opportunity to experiment with it.

X-Lock construction under way

Anyhow construction of the X-lock has now commenced, hopefully it can be finished off tomorrow, with luck.

G8LBT flies again, or is it nostalgia taken a step too far?

Those who have seen my QRZ.com entry will know that I have been planning to resurrect my old G8 call. This has now happened, the paperwork arriving today. So I am now the proud owner of TWO UK callsigns!

It's a wee bit curious why as to why this is permitted, and though I tell myself I am not one to covet another man's possessions, when I learned some while ago that some of my radio friends were in possession of both their old class B callsign and their more recent one, I felt I had to join this particular club.

I have had one or two arguments with folk who say they were told upon upgrading their licence when they achieved the Holy Grail of the 12 wpm morse test, or whatever, that they could NOT keep their old callsign.

However, the current regulations allow for (and this is quite clear from the text of the current Amateur Licence Application Form OF346) that a LAPSED licence (Class "A" or Class "B") previously issued to the applicant can be reissued upon production of certain documentary evidence that the applicant did at one time hold that callsign.

This latter condition wasn't too difficult for one such as myself who hardly ever throws anything away, and faded correspondence between myself and the then regulatory body (Home Office) was scanned and reprinted, catalogued with a covering explanatory letter and compiled into a dossier complete with OF346 filled in, and hey presto, two weeks later G8LBT was reborn!

I'm still not quite sure why I did it! Maybe it rolls off the morse key a little more nicely than my G4 one?

eQSL- why are so many hams so "sniffy" about it?

Apropos of nothing, today I received one of the occasional EMails I get say that there was an "eQSL" awaiting me at www.eqsl.cc.

When I logged in I was greeted with the news that my membership had been "downgraded" (in other words I hadn't made a financial contribution for over a year), so I duly fired up the PayPal screen and bunged them a few quid, as I have always thought that this service has been worth supporting. No big deal.

However this prompted a mental process which recalled all the "please no eqsl" messages I had seen scrolling across the screen whilst operating PSK modes, and I thought to myself "Why the heck not?".

It's completely understandable view from someone who has no PC or internet connection, but my experience is that the vast majority of hams across the world are now connected to the 'net, and therefore by definition (almost) must have a PC available to assist them in their hobby. Certainly virtually every PSK operator has a PC, as that is how that mode usually operates!

I realise that there are "issues" with eQSL not being "acceptable for awards", probably due to "authenticity" issues, (from the point of view of one who _doesn't_ chase awards), but on the whole I find it a splendid service; easy to use, inexpensive (you can use the system completely FREE OF CHARGE if you wish, albeit with some limitations in functionality, which I think is a pretty fair deal), and reliable (I can't recall any service outages over the period I have been using it).

The "accepted" alternative is the ARRL's LotW (Logbook of the World), which, apparently addresses the "authenticity" issues, but which is an absolute pain-in-the-arse to use (IMHO), and doesn't produce any kind of "QSL card" which eQSL does. When my LotW account needed revalidating recently, I had a heck of a job remembering and working out just how I was supposed do do it, and although I got there in the end, I was almost on the point of giving up before I hit on the correct combination of actions.

Some hams like to plaster their shack walls, or fill shoeboxes with pieces of cardboard commemorating contacts - I'm not included in this list, being perfectly happy to have a line in a logbook, or an electronic record such as eQSL.cc provides, and I accept that it "takes all sorts", but "PSE NO EQSL" does seem to be a "dog in a manger" attitude to me!

One QRZ.com entry I came across the other day stated that paper QSL cards were "honourable", and implying therefore the eQSLs were not. I think you can tell that I do not share this opinion.

JT65-HF - remarkable!

I've been using Joe Taylor's weak signal modes for a while now, mostly WSPR, but recently my attention has been drawn to an interesting spin-off which calls itslelf "JT65-HF".

Clearly many people have been there before me, as there is quite a bit of activity in this mode, which seems to be able to produce quite remarkable and astonishing results.

Having downloaded the software, set it up (easy peasy) and left it running for some hours, the resulting decodes have never ceased to amaze me, given the modest aerial setup I have here.

I presume that much of this is due to the "FEC" (Forward Error Correction) associated with this mode of transmission. Stations such as mine with modest capability therefore stand a good chance of getting their messages through, or conversely can successfully receive weak transsmissions from elsewhere to a remarkably high degree.

I would recommend anyone at least to have a look at this mode, and at what it can do.

ROPOCO SSB - a selfish rant

I will be the first to admit that this is a very selfish point of view, but I really am quite annoyed (well as annoyed as I will allow myself to be over something which is a hobby/leisure activity) that the "powers that be" whoever they are, have turned one of the twice-yearly ROPOCO contests from a CW challenge to an SSB or phone one.

Especially ROPOCO1 (April) in which I have previously participated many times.

I am not a contester at all, but I really enjoy this particular challenge as it is, quite frankly, just that, a challenge.

What it challenges, from my own selfish point of view is one's CW sending and receiving ability/technique.

It does this in quite a different way to that of most if not all other contests in that _ACCURACY_ is prized above all else.

Most other contest have so many elements which are predictable (report, serial number, region, and so on) that "quantity" rather than "quality" carries enormous weight, whereas in ROPOCO accuracy is king.

Sending technique and accuracy is challenged. In other forms of amateur CW communications the odd sending error is normally of little consequence - the operator who knows he has made a mistake in transmission has to decide whether or not to correct that mistake, and if he decides to correct it, he has numerous methods open to him how to achieve that. In CW conversation, he will often just let the mistake go and rely on the operator at the other end picking up the error and dealing with it in his own way.

With ROPOCO this concept just doesn't work, and the challenge is for both the operator sending, and the operator receiving knowing how to deal with what they think might be a mistake in either transmission or reception. Mistakes lose points!

If you have never participated in ROPOCO this notion might be somewhat lost on you, but those of you who have will know exactly what I mean.

It could be argued, and I am sure that it will be, that this format should translate perfectly well to a "phone" format, and I am sure it will, but my point is that the corresponding challenge in speech communications is quite different to that in telegraphy.

For my money, I "they" wanted to try out ROPOCO in speech form, they should have had an _extra_ contest for the speech boys and left us brass pounders with our twice-yearly bout of fun.

The reason why I am so narked that the April test has been changed is simply because that is the one I usally participate in!

How selfish is that?!