Light from the past

I recently found this beautiful GEC street light from the 50's on Ebay. It dates back to a time when we actually manuactured things in this country of ours. Of course being old it is made from girders, pig iron, porcelain and glass, and not cheap bendy plastic. As an ageing electrical engineer I have great fondness for such items. Of course if it was coming to live with me it was going to have to work  for its living and it was soon fitted over our front door. I even tracked down a clear mercury lamp to give an authentic light output from the 50's.  


A very different bedside clock.

Long before the LED, when the first number-crunching machines were developed, people looked at the problem of displaying numbers electrically. Various solutions were found, including tubes containing tungsten filaments in the familiar square 8 pattern that is still used today. All digits can be extracted from a combination of the seven segments. Obviously one problem is that with 8 wires being used for each digit, the spaghetti soon builds up when you have long displays. Luckily LEDs can be switched off and on very quickly so they can be 'multiplexed'. This is a sneaky method of lighting each digit one at a time down the same wires, but just doing it so fast your eyes can't see it. This means the same set of 7 wires can be attached to each digit and then each digit lit in turn using its 'common' 8th wire. A ten digit LED done conventionally would use 71 wires! Multiplexed it would use 17. A no-brainer then.

The Nixie tube was one of the answers to the problem. Often seen in 60's films to denote a countdown to the detonation of some bomb, only to be cut short by the hero with a second to go, after he cuts the blue wire just in time. (If I made bombs I'd make ALL the wires blue)!

I think it was the Russians that developed the Nixie tube, in fact they are probably still used in their computers! Anyway they are just a series of wire digits stacked together  in a valve full of neon gas, with a grid for a common. Applying a voltage to each digit makes it glow.  Simples!  

Obviously neon doesn't glow at 5 or 12 volts, so an on board switchmode makes a higher voltage to excite the tubes. This is cleverly pulse width modulated by the processor to allow night dimming. The colons are just made from those neon lights out of normal socket outlets. The great thing about Nixies is because of the fast response of neon, they can be multiplexed. The processor here is only lighting one digit at a time, but human eyes, and cameras are fooled into thinking that all the digits are lit.  The blue underlighting LEDs are just for effect and can be set to switch off during sleeping hours.

There are various kits available on Ebay, or if you're feeling brave you can build your own and write the code to run it. It isn't actually too bad. A 65Khz crystal is used to drive timer 1 in the microcontroller generating a one second interrupt that runs software decade counters to update a string of output registers. An interrupt service routine updates these every second and another routine constantly sends the contents of these registers at around 100Hz to all the digit pins of the Nixies and strobes their common lines to achieve the effect of different digits on each one.  

Yes. That's why I bought a kit!


                                New rotary spark gap for Tesla Coil.

After the disasterous melt down of my new rotary spark gap it was time to build another. My first failed because the temperature
of the electrodes melted the plastic. My modifications include the use of a PTFE disk which can stand much higher temperatures,
combined with larger electrodes to dissipate the heat, and the directing of the angle grinder fan output to cool the disk. Hopefully
this will work, but I won't know until we fire it up.

                    Oh dear, it melted.                              New version, with attitude.  




The portable hoot....

I live in a typical middle class, middle age, community of pullover-clad Daily Mail readers. Some years ago there was
a fault with someone's intruder alarm, causing it to let out a strange electronic squawk every so often. It was such a short
sound that you could not pinpoint where this odd noise was coming from. I heard it a lot but didn't pay much attention to it
because I am fairly relaxed about such things. However to the local middle-class busybodies, something like this was an
outrage, and I had people calling at my door asking if I knew anything about it. I wanted to tell them to just get a life but politely
said I had heard it but didn't know, and didn't particularly care where it was coming from. 

This was a few years ago and it gave me an idea. I would build something that made a stupid noise and hide it under
bushes near the road and have a remote control that I could press from the house to trigger it at any time I wanted. Even if
I got up to go to the loo at 3 am, I should give it a quick press just to keep them on their toes. Well that's what I did. I got a vintage
type Klaxon horn that goes AAAAOOOOOOOGAAAAHHHH!! (That's the best I can do in text), screwed it to a car battery,
and with the addition of a little receiver, I made my portable hoot. I have been hooting now on average twice a day for about
three weeks, and I just know that somewhere out there is a busybody obsessively  logging the date and time of every hoot.
I know, I'm barmy but it gives me a warm feeling inside when it lets out an AooooGah at 3 am!                                                                       

  My remote control. This is a radio door contact from a burglar alarm.

The business end. Battery, antenna,
receiver and relay inside the butty box


                         The Spud Cannon. Dangerous shit alert again! Don't mess with stuff like this.

                                   I love spuds. Whether fried, boiled, chipped, roast or jacketed.... or even shot half a mile out of a drainpipe!

I decided I would build a spud cannon. Don't ask why, I just did. All you need is some plumbing bits, something to create
a spark, a suitable aerosol and a lot of spuds. You need a combustion chamber, here built from 4 inch turd pipe and a barrel,
built from 2 inch waste pipe, 2 electrodes for detonation and a lid you can screw on fast. Sharpen the end of the spud barrel
so it will cut the spud as you press it in. Use another piece of pipe to ram it down to the bottom. I used a neon transformer for
my ignition spark but anything that creates a spark will do, even one of those clickers for lighting gas burners.  


The spud cannon, and close-up of the
spark gap inside.
Sharpened barrel and spark transformer.

hjghjf CAUTION!!! This spud gun is dangerous and probably illegal (most things are).d