GB8WW

A nice E-mail from Ofcom arrived with a Notice of Variation attached to it. This permits operation of a special event station GB8WW for the Mills on the Air weekend, 14/15th May 2016. So we are looking forward to a bit of portable operation at the Open Day for National Mills Week at Willesborough Windmill. I found and scanned a nice picture I took at an open day in 1994 - not much has changed!

Hoping to operate the station with my good friend Peter, G8WMZ, and any other willing volunteers who can be found.

Hope to work you on the air in May. 73

Hugh M0WYE

Tim Peake ARISS Contact

Used my Yeasu FT60e and an HB9CV to listen to astronaut Tim Peake as he conducted a  schools contact with a school in Rickmansworth.
The clear sky gave a good visual pass, so pointing the antenna quite easy ... manual satellite tracking. I made an audio recording that I have edited into a YouTube video, here...
https://m.youtube.com/watch?v=nNLsvPfyHG0

Making Plastic Objects at Home

After a seeing a comment about some rather tough Jarlsberg cheese on Facebook, I was reminded that milk was once used to make a kind of plastic - casein plastic was used for buttons and other small items. Manufacture of this material is possible at home. I turned to my copy of "Chemistry Experiments at Home for Boys and Girls" - a 1949 book by H.L.Heys M.A. (Cantab). Such publications as this would not be encouraged nowadays, but in 1949 making plastic objects in the kitchen was aparently well within the abilities of school boys and girls.  Here is the recipe...

73 Hugh

Replacing the LCD module on a Yamaha DX11 Synthesizer

So here is the problem. The LCD on my Yamaha DX11 synthesizer has faded so much that I can barely see what instrument I am playing - as you can see in the photo above. It appears that the seals around the edge of the glass panel have failed, because the fading started at the outside edges and has progressed inwards. When switched off the LCD is a peculiar pink colour, which you can see in the photo below. The old LCD is on the right, a new one on the left. (Note that I have already transferred the plastic bezel from the old LCD to the new one - it is held in place by a double-sided adhesive strip).

But where do you get replacement parts for an instrument which is probably over 30 years old?
I opened up the the synth and measured the size of the thing and then trawled through catalogues looking for similar devices. I found the Displaytech 162B-BC-BC looked to be the right shape and size, and the row of pins was in the same position along the bottom edge. The Displaytech part has 16 pins instead of 14, but I could see from the datasheet that pins 1 and 2 were connected to the backlight. It was readily available from RS Components at £7.94 (Part number 532-6379) so I ordered one.

While I waited for it to arrive I found the Service Manual for the DX11 on line, and that confirmed that, apart from the two extra pins for the LED backlight, the connections were exactly the same on the two displays.

I had to extend the wires on the LED backlight, and my attempts at desoldering the 14-pin header on the old display were unsuccessful, so I cut the wires one by one, and soldered them to the new display module. The wiring between the connector and the module is 1 to 1, but since the wires are not colour-coded (except for pin 1), it is wise to move them one at a time. In the picture below, you can see the LCD module, nestling in the middle, between the larger PCBs. It is held in place by a metal surround which is secured by a single screw.

 This picture shows the two modules side, by side, before I transferred the wires, so the old one is on the right and the new one on the left.

 The picture below shows the new module in position, with the metal surround back in in place and the LED backlight lead waiting to be connected back in the socket on the main board.

It was a great delight to see the new panel light up with nice clear text. I was expecting to have to make some adjustment to the contrast control resistor, but this was not necessary. The Displaytech module seems to be electrically very similar - even the character fonts seem to be equivalent. A thin metalic strip of the bezel is visible at the top and bottom of the LCD window, and it might be nice to black that out with a strip of black tape or even marker pen. But I couldn't be bothered to take it all apart again.

Happy Christmas and 73 to you all.
Hugh M0WYE

Apparatus for the Testing of Christmas Tree Light Bulbs

Apparatus for the testing of Christmas-tree light bulbs. I got very frustrated trying to test Christmas-tree light bulbs using a multimeter. Almost impossible to hold the probes on the little wires. I thought about making some kind of bulb-holder, but then hit upon this idea, using a wooden clothes peg. 

Copper tape is wrapped around the ends of the arms and secured with a soldered joint on the outside of the peg. Wires are attached and connected to a battery which can be conveniently carried in a pocket.

The peg is clipped across each bulb as it is removed from the chain. The battery should be chosen appropriate to the Voltage rating of the bulbs - mine are 2.4V - so a part-used "C" cell makes the bulb glow dimly, Note small screw positioned between arms of peg to prevent it closing fully, this is important as it prevents the battery being shorted when no bulb is present. 

Even though it was dark by the time I had finished it, I was still able to get the set working. The wires on some of the bulbs had become tarnished and so there were multiple"failures" within each series string of bulb. The tarnish seems to be due to age rather than moisture as the new bulbs in the pack had also gone the same way. Happily a little scraping with a craft knife soon got them going again.

Happy Christmas and 73 to you all.

Hugh M0WYE

I am the proud possessor of a Tesco Hudl (Mark 1). For those that are not familiar with this marvel of modern technology, it is an Android Tablet computer, with a 7" screen and all the usual features that this class of computer offer. It has a built-in compass and accelerometer, and of course GPS receiver, so that it knows its position and orientation on the planet's surface. I have been using the "Augmented Reality" App called Stellarium which puts a planetarium on your tablet screen, and, if you enable the feature, when you hold the tablet up against the sky it will show all the stars and planets in their correct positions ... or at least it should do.

Conjunction of Jupiter and Venus on 30th June 2015 (Top left of image!)

Conjunction of Jupiter and Venus on 30th June 2015

It worked when I first installed the app, but recently I have found that the screen won't turn when I do, it always points in the same direction. It was very frustrating, standing out in a field with my son, looking for the conjunction of Jupiter and Venus, and not being able to locate the planets in the sky. Today I realised what the problem was.

On a recent visit to Tesco I noticed a box of nice leather Hudl covers being sold off cheap. Now that the Hudl2 has been released, I guess the accessories for the old model are not selling so well. Ony a couple of quid, so I popped one in the shopping basket. It protects the screen nicely and can even be used as a desk stand. The magnetic catch keeps it closed when not in use ...
Ah ha! - what kind of a product designer puts a magnetic catch on a device which contains a compass?!

I wonder how many other people have been confused by this.
73
Hugh

0603 Resistor Codes

I was looking at a Printed Circuit Board populated with 0603 size surface mount resistors and puzzling over the markings. In particular R45 and R56 in the photo below. They are marked 18C, but the actual value is 15k.

 Now in the old days resistors were colour coded, and we all knew the code off by heart, Black = zero, brown = 1, red = 2 etc. There were usually three colour bands - 1st digit, 2nd digit and a multiplier which represented the number of noughts. So 4.7k was yellow, violet, red, for example. There might then be a gold band for 5% tolerance, or brown for 1%. Even when "E96" values came in, and many more "preferred" values were needed, it was just a case of adding another colour band to make three digits and a multiplier. This system was carried over onto surface-mount parts, but in numerical form. You can see some examples below - there is a 473 (47k) and a 223 (22k). But there is also 01C  and 30C which don't make much sense.

The answer to this is, of course printed in the data sheet for the resistors. It is is a way to address the problem of marking E96 values - presumably 0603 size parts are deemed too small to put four digits on. 

Perhaps an aside about "preferred values" might be appropriate here (although there is a very good Wikipedia Article about it). When a resistor is manufactured there is a tolerance in the value, perhaps +/- 10%, or 5% or 1%. So a 1000 Ohm resistor might be, say, 5% high (1050 Ohms). So there is no point in making a 1050 Ohm resistor because the value would overlap with 1000 Ohm. The next "preferred value" is 1100, because a 1100 resistor which was 5% low would measure 1050. For 5% tolerance resistors there are 24 non-overlapping values in each decade, and the sequence of values is called the E24 series. 10k, 11k, 12k, 13k, 15k, 16k, 18k, 20k, 22k, 24k, 27k, 30k, 33k, 36k, 39k, 43k, 47k, 51k, 56k, 62k, 68k, 75k, 82k, 91k, For 1% values there is an E96 sequence which requires three digits to represent each value. You can see this sequence in the table below which gives the manufacturer's 0603 resistor code on the left and the E96 value on the right. The Letter is the multiplier code.

So "18C" is indeed 150 x 100 = 15k Ohms. 30C is 20k Ohms, and 01C is 10k. All has become clear.

Now to print out this table and pin it up at my work-bench!
73
Hugh