Monday, 31 October 2011

Pedalling like Fury

I was fortunate to pick up an old, worn, dirty set of Hamond C3 padals on eBay for a fiver back in August. Here they are at the start of the "resurrection" process...

After a lot of elbow grease (most of it from my wife, who generously contributed her domestic skills and cleaning products) the pedals looked much cleaner. They also worked rather better, as I had replaced any badly worn felts, some of which support each pedal laterally between vertical guide pins. Finally, I had stripped off the galvanized brackets which support the operating "tabs" which do the actual switching in the real Hammond Organ (which is why this is a "resurrection" rather than a "restoration").

From this angle, perhaps you can see why I believe the previous owner(s) preferred playing in the key of F!

I wanted to use these pedals in my virtual organ project (Blogs passim), which meant that they had to be able to operate as electrical switches rather than hinged pieces of wood. There are a few technology options here for the organ builder:
  • you could arrange for each pedal to touch and operate a miniature switch as in this example
  • you could make electrical contact pairs (or one contact per pedal and one or more busses) for each pedal and make a physical switch as in this example.
  • you could use an optical method, with a "shutter" tab on each pedal and a opto-detector making the translation from optical intensity to an electrical switch function
  • you could use a magnetic method, placing a magnet on each pedal and using a Hall Effect sensor adjacent to each pedal to convert the magnetic field to an electrical switch function
  • you could usea magnetic method, placing a magnet on each pedal and using a reed switch adjacent to each pedal to convert the magnetic field to an electrical switch function as in this example
There are examples of each of these methods on the internet.

I wanted to use the Hall Effect method, but I couldn't find the sensors cheaply enough (you should know me by now), so I stuck with the trusty, cheap reed switch technology...

I put 3mm Neodymium rod magnets into a hole drilled in the end of each pedal...

You can see the vertical guide rods and the felts, mentioned previously.

I also made up a series of perspex panels (chosen for its transparency, which made alignment with the magnets during "marking up" and subsequent assembly easy), each holding five or seven reed switches. I made brackets to support these panels, mounting under the nut and lock washer that secured the guide pins - the whole process involved no "butchery" of the pedals, except the magnet holes. One of the (five switch) panels is seen, in-situ, below...

I have described previously how my single-octave pedals were wired up and converted to MIDI. The same process was used again - with one significant exception...

The pedals are scanned as a matrix of (4) columns and (7) rows, the last having only one pedal (25 notes takes 6 rows of 4 and a single "extra"). In the previous encoder system, it was known that you could not play more than one pedal in a single column together whilst playing another pedal from another column without the possibility of additional notes sounding. This wasn't seen as a problem as playing two pedals in one "column" constitutes an interval of a minor third or less, which isn't done in the bass register (it is psycho-acoustically and musically meaningless).

However, the geometry of the new pedalboard made it easier for me to arrange that the reed switches should be normally on, switching to open circuit when a pedal is depressed. This meant that, from the point of view of my encoder scheme, all the notes in every column were being "played" most of the time - the system didn't work!

The solution is well-known and simple - you just add diodes in series with each reed switch et voila. Of course, I had to invert the logic of my encoder program (to send a "Note On" command when a reed went open circuit and vice-versa) but that was the work of moments.

Here's the expanded version of my pedal encoder system, capable of running 25 keys (plus seven spares for "toe pistons" or whatever) and the expression pedal...

The trouble with a two octave pedal board is that you need a real organ bench to sit "over" the pedals. Fortunately, eBay came to the rescue again, with a genuine Hammond A-100 bench...

I'm very surprised how easily this went together - I was frightened that the reed switches would be very difficult to set up, but they were easy. Careful location of the magnets (using a jig to drill the pedal ends) and equally careful marking up of the perspex carriers made it work first time.

All I need to do now is get out of the habit of stopping at that formerly top - now middle C!

...-.- de m0xpd

Wednesday, 26 October 2011

Shelving Audio Filter

I was fortunate to pick up a Leslie 825 speaker for my virtual organ project (Blogs passim) for a song on eBay...

Part of the explanation for the attractive price was that - as the seller put it - this is "a Leslie 825 speaker with a difference".

I'll let the seller go on with his description:

"the difference is that the (previous) owner had a number of keyboards and he modified the cabinet by inserting two other speakers front and back - he drilled holes in the cabinet and placed a grill over the front - the grill is available but is not in the picture so that you can see what lurks beneath".

Well, now YOU can see the ugly array of holes in the picture above. I have fixed the grille on to make thinks look a little less unsightly and, like the seller, I haven't yet bothered to test the additional speakers. But the Leslie itself works well enough (with one trivial exception, to be described below).

For those of you who don't know, a Leslie speaker includes rotating mechanical elements (horns and/or baffles) to introduce a cyclical variation to the radiation from the loudspeaker which, in interaction with the acoustics of the performance / listening space, makes some interesting spatial audio effects involving amplitude and frequency modulation and comb filtering. It was developed by Don Leslie...

in an attempt to emulate the chorus effect produced when ranks of (inevitably somewhat de-tuned) organ pipes speak together, giving electronic organs a "pipe voice". The mechanical components are contrived to rotate at one of three different speeds (slow/stop/fast or, to respect the orthology, chorale/stop/tremolo) under the control of the iconic "half-moon" switch. Paul, g1dva, tells me he has seen rotating speakers with continuously variable speed control - but we'll dismiss these as pathological. Certainly, the classic Leslie only operates at a few discrete speeds, latterly the three described above.

Older Leslies used a horrible electrical interface, in which mains power, control signals and the audio were all applied through a long, multi-way cable terminated with special (i.e. expensive) Amphenol connectors. In the case of the 825, it is a 9-pin system, with the following connections...

3YellowNo Connection
4OrangeStationary Input / Aux Control (not used in 825)
5Greendc Output (+28V)
6WhiteSlow Motor Control
7VioletFast Motor Control
8Gray240V In
9Blue240V In

(The colours are those of the cores of the "official" Leslie Cables).

The seller of my 825 kindly gave me a 9-pin cable to connect up the device - thanks Bob!

Well, I had the cable but no socket for the organ end, so I lashed things together with a very unsafe Heath Robinson connection, involving individual pieces of "Choc Bloc" connector...

on each of the pins of the plug - DO NOT TRY THIS AT HOME, CHILDREN!

All this gave me opportunity to confirm that the speaker was working, to bask in the glorious spatial effects of a real Leslie (emulations only work up to a point) and - after the honeymoon was over - to become disappointed with the sound!

The 825 has no horn (and associated HF unit) - only a large "full-range" speaker firing through a rotating drum. In consequence the top end is hardly what might be described as "sparkling". In fact it is so poor that I began to think there was something wrong with the "key click" function in the fantastic VB3 software and I actually contacted the programmer before realising that the problem lay right there in my new 825 - sorry Guido!

All this led to some creativity - I acquired a 9-pin socket to replace the temporary lash up (thanks George) and I decided to build a filter to boost the HF response and try to rescue some of the sound. The (sound card) output from my virtual Hammond wasn't enough to drive the speaker to satisfactory levels, so a Pre-Amp stage with some gain was indicated too.

Here's my HF shelf filter, seen as an extract from the LTSpice simulation of the entire circuit...

The series combination of R5 and R6 was actually realised with a potentiometer, configured to give me a variable HF lift. Here's the magnitude response simulated in LTSpice for an arbitrary setting...

The lift above 1kHz is the "shelf", made into more of a "bump" by the low-pass corner (deliberately) introduced by R1||C4.

I turned the idea into reality in a nice sloping front RS box, picked up at a rally somewhere, intentionally copying the format of the Leslie "Combo" Preamp. Here are the innards...

and here's a view of the back panel...

In addition to the variable high frequency shelf, there is an internal jumper to select 0, 10 or 20 dB overall gain and an external volume control. I haven't had chance to fit knobs to the controls yet!

There is (as is usual) a fly in the soup - the "d.c. output" from my new Leslie (pin 5) isn't working. I looked at the schematic and there is little to go wrong (I suspect a dead diode, D14, or an open connection), as the d.c. comes straight from the power supply to the amplifier driver stage, which most emphatically IS working! Still, at the moment, my new PreAmp is powered from a PP3 battery.

Result - FANTASTIC. The 825 is totally transformed and a pleasure to use.

I have some rather more exciting Leslie-related stories to tell - but they can wait for another day.

For now, I'm all in a spin!

...-.- de m0xpd

Update: Fly Rescued from Soup!

This evening I made up a shorter cable for the 825 - having 30 feet of cable coiled up is a recipe for trouble, not to mention hum. I so doing, I discovered that the 28Vdc issue isn't a speaker fault at all - just an intermittent connection in the long cable. The shorter one is fine (with new connectors) so now the PreAmp is powered from the Leslie as planned.

Tuesday, 18 October 2011

Most Secret War

Just finished reading R.V Jones' autobiographical book "Most Secret War, British Scientific Intelligence 1939 - 1945"...

being an account of his work as leader of the Air Ministry's Scientific Intelligence Section in WW2. In short, the book is a masterpiece and a must-read for anybody remotely interested in some of the technological and scientific tussles between the allies and the Third Reich.

I purchased the book during my last visit to Bletchley Park and there is obligatory mention of the activities of the Code-Breakers in providing the most reliable of data streams for the Scientific Intelligence community in the UK - an "anchor of truth", as the author describes it (p 530).

There is much else to entertain those with radio-related interests - including the detection, understanding, prediction and ultimate jamming of the radio navigation beams by which the Luftwaffe we able to achieve accuracy in their bombing activities and the similar location, interpretation and jamming of the radar systems which allowed German night-fighters to engage Bomber Command missions over Germany. However, beyond these triumphs, it was the author's involvement in the development and deployment of the countermeasure we now call "Chaff" - then inexplicably known as "Window" - which impressed me most.

This is a giant of a book, fully deserving the hyperbolic notices which adorn its paperback cover ("Among the best of all war books", "Every bit as good as a Deighton or Le Carre Yarn").

Yes - this deserves to be read. Unfortunately, in reading it, I found myself admiring Dr Jones' achievements but becoming anything but warm toward him as a person. Perhaps that's a by-product of the determination and single-mindedness that made him so successful in his great work.

What would I give for determination and single-mindedness?

Not a lot!

...-.- de m0xpd

Wednesday, 31 August 2011

Requiescat in Pace

Saddened to hear news of the death of Anthony Edgar "Tony" Sale, whose work on the rebuild of Colossus was central to the preservation of Bletchley Park and the establishment of The National Museum of Computing.

Tony was there tending his creation when I visited Colossus last year - he leaves a legacy not only in the physical rebuild of the machine, but also in the enthusiasm he fostered in a team of colleagues who helped with the rebuild and now ensure the preservation of some important pieces of history.

...-.- de m0xpd

Sunday, 28 August 2011

A Splendid Jaunt

Just back from a few days in the beautiful surroundings of Pickering, North Yorkshire, where we stayed in a delightful cottage conveniently positioned mid-way between a trout lake and a railway station - the very 'gate of heaven'!

Whatever Kirstie and Phil might bang on about, this establishment didn't just rest on its location laurels - it was beautifully presented as well. In addition to the little two-bedded cottage in which we stayed,"The Limes", the good folks at High Mill also have a larger property for rent, which sleeps up to 12.
The view from my armchair was fantastic - here's 7F 0-8-0 heavy duty freight locomotive 49395 working a passenger service tender-first back to Grosmont...

We took the same trip ourselves a few days later, travelling back from Grosmont in fine style in the first class observation saloon at the end of a nice rake of wooden LNER coaches (you can see the new Barbour Beaufort I got from the Orvis store on Pickering's Market Place hanging over the back of my armchair)...

The staff at the Orvis store deserve special mention as they honoured the "£20 off" voucher that came with our railway ticket, even though I'd purchased the coat two days before!

Things took a turn for the better when some thoughtful chap came and offered us drinks - here's my "Gin and Tender"...

(the tender being that of the 9F engine 92214 "Cock O' The North", which strained and sighed on the other side of the glass whilst pulling us back to Pickering).

Here's the observation saloon from the outside on reaching the shelter of Pickering Station's new roof...

Aside from many other notable delights (Gannets at Bempton, the Castle atop the hill behind High Mill and a sublime piece of rib-eye steak at The White Swan), the trout lake served up its usual entertainment...

I think it is actually bigger than the one caught in April - certainly your humble servant looks pretty pleased with himself...

If you want a break in a great location, give High Mill a try - seen here photographed from the observation saloon...

I certainly will be going back.

The only fly in the soup was the trouble I had getting any signal out (2W on 40m CW from the FT817 and Whip). Still, the Mill is on a road called the "Undercliffe" - the clue's in the name!

...-.- de m0xpd

Saturday, 20 August 2011

Heavy Artillery

The same sale of surplus gear that bumped up my BNC socket stocks also saw me bid a tenner to win a wideband RF power amplifier, which runs 12 Watts, 200 kHz - 32 MHz, made by RF Power Labs, Inc. of Kirkland, WA. It had Albert, G3ZHE's sticker on it, so I knew it had come from a good home. Albert told be that previously it had been in Jim G3NFB's shack - it is nice to be keeping it in the Warrington family!

Today, I had chance to power it up and see what it does...

I hooked it up between the output of my multi-mode beacon (Blogs passim), which happened to be set to the 30m band, and the G5RV. Here is the "brick" on the bench...

You can just see one of my switched attenuators atop the amplifier, throwing away some of the input (the amplifier needs 1 Volt in for full rated output).

I was immediately spotted on WSPR in the USA by Edmund, WB1FIG, in Plainville, Massachusetts...

having previously only been heard in Europe.

I do get into the US on occasion with the standard 50mW on 30m, as demonstrated last night, when Douglas, W3HH, heard me once again in Florida...

Having fired WSPR signals over the pond with my new "big gun", I had a look to see if my other modes were being heard further afield. Sure enough, I could just make out my FSK-CW and Hell signals on Bill, W4HBK's grabber in Florida (although you do need to know where to look)...

Of course, the QRSS modes into Europe were loud and clear, as seen on Joachim, PA1GSJ's grabber...

In fact, Joachim was also reporting spotting my WSPR signals both during and after the 5 Watt QRO test. Switching from 5W back to 50mW is a x100 change in power (-20dB) and, sure enough, Joachim's reports showed pretty much a -20dB degradation in SNR between two adjacent spots...

So - the bench RF amplifier works a treat.

Apologies to anybody offended by the fact that I couldn't be bothered to change reported power in my WSPR message during the short test - it is a chore re-programming the PIC - mea culpa!

...-.- de m0xpd

Sunday, 14 August 2011

Italian Job in Toytown

The XYL's father is something of a model railway enthusiast - the photo below reveals the ironic understatement...

During our last visit (in which I took the photo), he asked me to make a traffic light controller - no doubt in an attempt to bring order to the anarchic road-rage one otherwise meets at a 1:76 scale crossroads.

Of course, a traffic light controller is a pretty trivial problem in Finite State Machines 101, so I quickly whipped up a system based on a PIC16F676, with on-board LEDs to monitor progress and open collector outputs to switch on and off the "grain-of-wheat" bulbs which the Toytown traffic engineers have used.

Here's the system under prototyping, connected to my PICKit2...

and here's the translation to a PCB...

All pretty dull. So I decided to fool around a little...

Readers will remember the havoc that can be wrought by messing with traffic lights, as demonstrated in the movie classic "The Italian Job".

I decided it would be fun to introduce an occasional state of confusion in the traffic signals on my father-in-law's railroad - so I programmed in a display which would look good on the Golden Mile...


(Interesting how the video - captured by my iPhone in low light conditions - is incapable of resolving the colour of the bright monitor LEDs)

The traffic light chaos only kicks off every 200 complete cycles, so you have to be watching the lights (or driving past at just the wrong moment in a 1:76 scale car) to see it.

Let's see if he notices!

...-.- de m0xpd

Monday, 8 August 2011

Appreciation as Grabber Goes QRT

A few days ago on the KnightsQRSS Mail List Johan, on5ex, announced that his excellent QRSS grabber is soon going QRT.

Johan and his grabber have been giving wonderful service to me and to many QRSS operators for many years. In fact, it was Bill Meara's talk of this mysterious station up in Belgium picking up signals from The Eternal City which started my interest in QRSS.

Johan became the second station to report seeing my own QRSS signals and has been picking me up ever since (including back in the day when my Hellschreiber was UPSIDE DOWN!!).

So - now its time to say a huge THANK YOU to Johan and to wish him every success in his new games with other radio modes.

73 dr OM Johan,

...-.- de m0xpd

Enigmatic déjà vu

I was lucky enough to find myself once again in striking distance of Bletchley Park yesterday and enjoyed another interesting visit. Just like last time, the Battle of Britain Memorial Flight treated us to a fly-past - this time by a Spitfire...

Having last time focussed much attention on Colossus, I was determined to spend a little more time looking at the Bombe (which itself has been the subject of a re-build project) ...

I was fortunate to be able to chat with one of the guides, who explained in considerable detail the operation of this impressive machine. I don't know her name or her background, but she certainly understood operation of the Bombe in depth and I am grateful for her expertise.

Talking about expertise, I was pleased to chat once again with David Wright, g3zpa, who gave me some more information about the original (long-wire) antenna systems supplied for use with the Paraset.

In addition to the aircraft flypast, there was an impressive gathering of classic cars with the inevitable superabundance of MGs (I'm allowed to say that as an MGB owner)...

However, other marques were well represented too. The car of the show (for me at least) was a drop-dead-gorgeous Alfa Giulia Veloce - but I was pleased to see some nice 3-wheeler Morgans...

These 3-wheelers are of interest partly because the XYL's grandfather used to own one and partly due to their pivotal role in the plot of Dorothy Leigh Sayers' "Have His Carcase". Morgans more generally have a place in my heart as the XYL and I went on honeymoon in a 4-4. Happy days!

Cars and aeroplanes aside, there was lots more to interest me at BP - not least in my first visit to The National Museum of Computing which, appropriately, is in the same building as Colossus. After seeing the PDP8's of my youth I was pleased to see a healthy display of analog computers (which - for those of you who don't know - solve differential equations by electrical ANALOGY) amongst which was something I'd never seen before: a hybrid analog AND digital computer...

In truth, it was an analog computer with a few digital elements (flip-flops etc) along the bottom "row" in the photo above.

I was also delighted to find an example of the main board from a Tangerine "microTan 65"...

One of my first computers was built around this 6502-based system marketed as a kit by Tangerine. There was a basic interpreter, a disk operating system and all sorts of goodies. Nice to see it again!

However, the high spot of my visit to the National Museum of Computing was certainly the Domesday systems, based on BBC / Acorn hardware and in the news recently because of the "Domesday reloaded" initiative. Here's one of the two working systems at BP...

We were staying with the in-laws, near Pulloxhill, Beds., so we used the amazingly modern multi-media interface to search for Pulloxhill and pulled up a picture of the characteristic water tower...

Here's a link to the photo on the web-based Domesday Reloaded resource.

Partly (I am told) in consequence of the recent financial debacle at the RSGB, the new radio centre isn't yet open to visitors...

... but we did call into the MKARS club house (in an old generator building on the BP "campus") where I had a nice chat with Graham, a G7 licensee (I missed the rest of his call), before driving back to Pulloxhill.

On the drive back we stopped to take an up-to-date shot of the water tower...

Sitting outside drinking a cup of tea half an hour later, the day was crowned by an unexpected flypast of a Consolidated Catalina, the conspicuous lines of which were unmistakable even at altitude...

I assume she was G-PBYA, which is "berthed" at Duxford - she certainly was heading in the right direction!

Perfect end to a(nother) grand day out!

...-.- de m0xpd

Saturday, 6 August 2011

Harvesting Parts and Knowledge

My attendance at weekly meetings of my radio club has been rather patchy of late (pressures of work intruding on the finer things in life), but my last visit coincided with a Sale of Surplus Equipment, at which we managed to capture some of the excitement of the last few minutes of Bargain Hunt (albeit with more desirable items for sale, naturally). In addition to a nice Linear Amplifier (which allows me to make vulgar QRO emissions at 12 Watts, should I ever want to get involved in EME or similar games Hi HI) I was winning bidder on an old piece of kit which bristled with silver plated BNC sockets - 19 in number...

Perhaps you can make out the label - "Junk but spare sockets". A 50 pence bid secured the item.

A side panel carried identifying marks, revealing the object to be from the Hewlett Packard stable...

but some searching on the 'net hasn't provided any more information on pedigree, use, date or other aspects of provenance.

Taking off the sides revealed a set of 11 parallel "channels" (ten of which are connected to BNC sockets on the "front" and the last of which leads to a socket mysteriously located off on one side)...

Casual inspection suggests the unit is some kind of switching/multiplexing device (the clue was in the name on the side of the box!!) with a number of input signals multiplexed onto a number of output channels, using diode switching. The channel select and other control signals apparently were applied through the Centronics-style connectors seen at the right-hand end of the photo above. The whole thing was beautifully built - seemed a pity to pull it to pieces - but here's one channel stripped out of the enclosure...

At this point I had completed the harvest of BNC sockets - now I was about to harvest a different resource.

You can see a line of devices in glass envelopes protruding from the bottom of the board in the photo above. Unsoldering one confirmed my initial identification as a diode and a quick test with the multimeter showed a forward voltage drop which suggested the diode to be of the Germanium persuasion.

I couldn't see any identifying marks, but the glass envelope was clearly marked with colour rings - as on a resistor...

I figured the colours were brown - white (or, possibly, grey) - green (with a rather indistinct black blob at the other end). I had never seen colour coding on a diode before - so off I went to the internet to search for an explanation.

I learned two important nuggets of information, completely new to me...

Firstly, colour codes - exactly those familiar to us from resistors - were indeed used on diodes and semiconductors in general. That made these diodes "195"s - but that didn't make much sense. Until I recognized a second fact which had been staring me in the face for decades; semiconductors were often named using a system in which the device type (i.e. diode) was followed by a numerical name. The device type was signified by the Number of junctions ("N" for number).

According to this scheme a "1N" device is a diode (there being one P-N junction defining a diode), as in the entirely familiar 1N4148. Similarly, a "2N" device is a transistor (there being two P-N junctions in a [BIpolar Junction] Transistor), as in the entirely familiar 2N3904. It is so entirely obvious when you think about it that I'm surprised I'd never realized before!

I am used to learning something about the nature of a valve/tube from its (alpha-numeric) name - as in an ECC83 being a double triode and a PCL86 being a triode-pentode, the E and the P signifying different heater requirements. However, despite a lifetime of using diodes called 1Nxxxx and transistors called 2Nxxxx, it simply never occurred to me to notice the significance of "1N" and "2N".

So - as well as a rich harvest of BNC sockets, I also had harvested some knowledge. Unfortunately, I'm still not yet out of the woods, because I don't yet know how to put all the pieces of the jigsaw together...

Does the "195" on my diodes mean they are 1N95s? Sure enough, there is a Ge diode called the 1N95. However, my internet researches suggest that the "1N" identification of a diode wasn't included in the colour coding scheme, suggesting that the diodes are 1N195s. The 1N195 seems to be a Si device, which isn't consistent with the 0.23V forward Voltage drop I measured.

If anybody can explain this, I'd be interested to hear from you.

...-.- de m0xpd