Homebrew telephone exchange – the multiple
As some of you know, I’m designing and building a telephone exchange from scratch. I’m aiming to use components which would have been available in the 1950s (with the exception of a bucket full of silicon diodes because I can’t find enough metal rectifiers or appropriate relays to do the job)
While all the techniques I’m using would be understood by a telephone engineer of the time, I can’t say they’d all be familiar as some of my circuit design is a little “non standard” – some bits of this exchange design would no doubt raise an eyebrow or two!
The exchange will have 20 lines in total, numbered 20-39 (In the photos, you’ll see them numbered “21-20, 31-30″ which is because “0″ is a “10″ in pulse dialling terms. If you’re laying out the lines in the order that the final selector would connect to them they go: x1,x2,x3…x8,x9,x0)
So, I’ve spent the last week and a half’s worth of evenings, making a start on the wiring the multiple. The multiple connects each line circuit to each of the 4 uniselectors (two are linefinders, used to detect someone wanting to make a call. The other two are final selectors used to route that call to another phone.)
If I’ve done my sums correctly, there are 298 wires, 358 soldered connections, 120 wire wrap connections, 40 diodes and 4 uniselectors on this frame. To connect it to the rest of the rack, I think I’ve got another 60 wire wrap connections and 100 soldered connections to connect the line circuits, then at least another 30 soldered connections to connect it to the control circuits (although that’s a bit vague as I haven’t quite finished designing them yet)
If you haven’t dozed off by now, you’ll notice that in the picture above you can see a Van Der Graaff Generator which is awaiting repair (I really must have another look for a source of natural latex straps) yet another telephone and a box of Atari ST games.
Now that I’ve built the multiple, the next step is to put it on the rack, and then turn my attention to the ringing machine (a wonderful combination of electric motors, tone wheels and cams which generates all the tones and ringing current required for a telephone exchange) – oh, and of course I need to finish the rest of the design.
Then again, it’s taken me 18 months to get this far. There’s no rush!
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Photochallenge catchup
Over the last 2 months, I’ve missed the following photo challenges:
So, in the spirit of catching up, I’m going to try and tick those subjects off the list. So far, I’ve only got two of them:
Green
That’s possibly the most photogenic bit of litter I’ve seen in ages.
Entrances to Hell
I’d love to know what’s behind that brickwork…
Now all I need to do is get my thinking cap on and come up with shots for the rest of them!
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Tyndale Monument, North Nibley, at sunset
I’ve been very slack about entering the photo challenge recently, so on Sunday I thought it was about time I pulled my finger out and went out to take a photo.
This weeks theme is “sunset” so that’s what I went looking for. I wanted to take a panorama, so I looked at a map and picked out a local hill (with a tower on top of it, as a backup subject) and set out. Half an hours drive, and 20 minutes walk later, I was on top of the hill at about 20 minutes until sundown. A quick bit of scouting revealed that while there was a glorious panorama on display – it faced south and there was a wood in the way to the west – no sunset panorama for me!
So, walking off down the hill a bit, I lined up on my backup subject, the Tyndale Monument set up the camera and waited. Sunset itself was a bit disappointing (not enough cloud to make it really work) but about 15 minutes after the sun actually went down, I got the shot above.
Not the best sunset I’ve ever taken, but at least I managed to get out there and try this week – and if nothing else, I know it’s not an ideal location to shoot a sunset.
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Bristol Zoo
I still had loads of energy left after my run this morning – so I cycled over to Bristol Zoo. Partly to burn some of it off, and partly to check that my ancient knackered old bike is ridable enough to possibly start cycling to work again. Their butterfly house is amazing.
I managed to catch feeding time for the gorillas, which was great because they’re only about a hundred meters away from you at feeding time. This is one of the babies.
And now… compare the meerkats!
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Here’s a photo of a steam train
They were having a “Steam Gala Day” at the railway yesterday. It was great! We were working in the locking room for the Lydney Junction signal box, and it meant we had trains rumbling past every 15 minutes or so (much more fun than once an hour on a normal running day!)
The engine above is in-between two autocoaches. I like this setup, as a series of linkages connect the throttle and brake controls to a position at the far end of each carriage. This means the driver sits at the front of a carriage and drives the loco from there. (Although the fireman stays with the loco to regulate steam pressure etc) When the train gets to one end of the branch-line, rather than having to run the engine round to the other end of the train before going back the other way – the driver just walks down the platform and gets in the other carriage.
Anyway I’ve mostly posted the above as an excuse for posting two things:
- This morning I ran 6.7miles (10.8km) which is the furthest I’ve ever run in one go. I did this without stopping, walking, or keeling over with an astma attack (yay!) So that route may become my daily route now. I’ve got no idea how long it took because I clean forgot to look at the clock before I went out.
- I’ve just weighed myself, and it seems I’ve just won the informal “race to lose a stone” contest at work. Just another half a stone left to go then I’ll be back to my 2002 weight.
I just need to bake a massive cake to celebrate now!
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