This is why I haven’t been taking photos or updating my blog this month.

What you are looking at, is the beginning of the telephone exchange I’m designing and building from old GPO components and circuit techniques. I’m designing it from scratch, picking and choosing circuit elements from various telephone exchange designs from the 1930s-50s.

Tonight, I managed to build the first two line circuits (there are enough relays in the image above for four line circuits, but better to start small!)  After a little bit of debugging (the connection tabs on the back of those relays are really confusing!) all the bits of wire have the voltages I’m expecting on them!  Yay!

Some of my prototyping methods are a bit vintage as well.  These are copper coated nails, which are used to make an impromptu wirewrap board.  This particular bit of prototyping is the subs-multiple.

The stuff I’ve built doesn’t really do much at the moment (apart from click a bit when you pick up a phone) and the next stage is to build the linefinder.  That bit is much more interesting as it spins round and makes nice raspberry noises.

I wonder if my video camera still works

I had a distinct lack of ideas for this weeks photo challenge.  So I decided to take a photo of something yellow, and invert the colourspace to  get blue.  To get the blue bananas I copied the base layer, inverted it, then set the blend mode on the new layer to “colour” (which preserves the white highlight and black shadows)

Apart from a little sharpening after the resize, that’s pretty much all I did.  I quite like the result.  Even if it is a little more “gimmicky” than my usual fayre.

This is Jon Peat, British Young Juggler Of The Year 2006, probably one of the most interesting ball jugglers I’ve seen in a long time.  He was trying out a new routine on stage at the BoB Juggling Festival this weekend. There are some more photos from the show in this album here.

However, the most productive part of the day for me, was my chat to Tarim about my idea for a telephone based siteswap validator.

The Background:
For those that don’t know, siteswap is a mathematical language for describing juggling patterns.  The idea is that you can use a string of numbers to represent the pattern.  Each number represents a throw event, with the number determining how many beats later the object is thrown again. Eg a 3 means that the object being thrown at that time, is next thrown 3 beats later.

Some strings of numbers are valid juggling patterns, for example 531 (which is a 3 object pattern) but not all strings are valid. For example, 540 is not a valid siteswap, as the 5 object is next thrown in 5 beats time, but the 4 is next thrown in 4 beats time. This means that they’re both thrown by the same hand at the same time. There’s a collision.

There’s a lot more to siteswap than that, if you’re interested in all the gory details start here with this wikipeida article about siteswap.

It’s handy some times to be able to check if a string of digits is a valid juggling pattern or not, telephone dials have digits, so they can be used as an input device. They also have earpieces, so can be used as an output device.

The Plan:
To build a device which you can plug an old rotary dial phone into, which allows you to do the following.

1. Pick up handset
2. Listen for a dialing tone
3. Dial in the siteswap you want to validate
4. Hang up handset
5. Wait a few seconds
6. The phone will then ring
7. When you answer the phone, a recorded message plays telling you if the number you dialed is a valid siteswap or not.

I had a firm idea about how to do all those steps apart from step 7, getting a microcontroler to play speech isn’t trivial. Talking to Tarim though gave me an idea of how to get around that though by using a cheap MP3 player.  Result!

I’ve built a circuit which interfaces to the phone line, and can detect hook state and count dial pulses. I can get audio onto the phone line. I know *how* to make the phone ring, but am lacking the components to do so.

In short, I’m *soo* close!

As I’m sure you all know, British phones ring in the following cadence: “0.4sec on, 0.2 sec off, 0.4sec on, 2sec off” – which is the one true timing for telephone ringing as far as I’m concerned. The USA do some kind of “2 seconds on, 4 seconds off” thing which is easier to generate, but really not very nice to listen to on a lovely GPO phone (My trimphone sounds especially “wrong” with the American cadence)

Anyway, we’ve been scratching our heads about how to make a relay click in the right cadence, to switch the ringing current in the telephone exchange we’re building.

Last week,  I sat down with my “Big Book Of 555 Timer Tricks” and sketched out the above circuit – but didn’t have enough of the right component values to build it.  Ian did have enough junk components in the right ballpark, so built it at the weekend.  And it works! Rah! He’s got video of LEDs flashing and everything!

The circuit uses two 555 timer chips running in Astable configurations, one generating a slow waveform which is used to turn on and off a second timer, which generates a faster waveform.  The upshot is that you get short bursts of the faster waveform at the output.  The on/off timings are written on the diagram, and are chosen so that you get two “on” pulses from the second timer in the time it takes the first timer to turn on. Bingo, GPO ring cadence FTW!

The interesting(?) bits of this are that the second timer is turned on/off using its reset pin, and that the first timer uses a diode to give a duty cycle of less than 50% – the fun bits are that my phones can now go “rng ring” instead of “ring”

So.  I have a plan!

52 projects, in 52 weeks.

2009 is to be the year that I finish all those little things I started work on.  It’s going to be the year that I build the “RS232 over tin-cans-and-string” thing, the year I build that ring flash out of disposable cameras, the year that I build a small scale AM transmitter so that I can tune the valve radio in my kitchen to the 1950s…

The rules:

• I have 52 weeks to complete 52 projects.
• Photos will be taken, build notes will be written up, software will be published.
• While I aim to average a project a week, completing two projects in a week then taking a week off is allowable
• Progress will be reported when it’s available, even if the project is as yet unfinished.

I’ll be maintaining a page which lists (and numbers) the projects, with links to the blog articles describing progress.  Wish me luck!

After ripping through a whole packet of balloons trying to get the distance between the balloon and the mic right – this is the best I managed. It’s not bad, but I think I can do better. Time to buy more balloons!

It works, but it ‘s going to need a little bit of practice to get any decent results. This is the best I’ve managed so far:

The next stages are to:

• Solder up what I’ve got, so I can use my plugboard for something else
• Build a delay box to give better control over when the flash fires
• Either buy a new flash with power controls, or modify my existing flash (Replace the LDR with a variable resistor) – a lower output from the flash should be a shorter burst of light, which will reduce the motion blur I’m getting
• Sort out a black background cloth, and arrange some more interesting lighting!
• Get myself a lense that’s better suited to this than the one I’ve got…

So, I’ve got a Nikon D80…

Off camera flash, ghetto studio setup can be seen in the setup shot…

Click the photo for details of how it was taken.

Unfortunately, my experiments are a little hit and miss as I don’t have the luxury of a digital SLR to learn my technique with. So I figure that if things are going to go wrong, I may as well encourage them and use the holga rather than anything consistent…