12 Boxing it up

So now I have a working exchange consisting of four lines, numbered 122,222,322 and 422. I made the numbers three digits just for the sake of it really. My first exchange used 11 as the post-fix so I used 2 this time just because. If the extensions are not dialed as above then it will be a false number and a fast busy tone is played to the handset.

Here it is boxed up and mounted on the wall. The segment display is used to describe call progress but when the exchange is idling it displays random characters generated every second just to show it's still alive. The red button resets the Arduino and the two black lumps on top are the fuses for the DC feed and the AC ringing. Above it are the junction boxes and batteries used by the Plan 7.

Removing the lid shows how the exchange fits in the box. The large single Veroboard shows the exchange itself, so from top to bottom, the powers supply caps and VR's, to the left the call sensing, in the middle the isolations transformers for the source and destinations lines, the opto-couplers and relays for the pulse dialing, ringing cadence and off hook (phone answered) for the destination phone. Below that are the relays making up the call routing. The transformer takes up a pretty huge amount of space but I just don't know of any small sized multitap transformers available that would do the job at a reasonable price, so I'm stuck with well over specified ones. At the top, behind the Veroboard so out of view, is the smaller ringing transformer. At the bottom running horizontally are the two other smaller Veroboard cards that contain the shift registers and tone generation components, stacked on top of each other. I have also mounted the Arduino onto this card. 

The MT8880 DTMF IC has been mounted on the same card as the shift out registers but I'm going to talk about implementing this in a different blog as at the moment I'm thinking about a re-design. It is shown in the middle, just above it's own isolation transformer. To the left is the ring detection circuitry used to answer an incoming external call and the relay to connect external incoming and outgoing calls.

Running a bit low on on space and a late edition I made up a connector block to link the four lines and the one external line and fixed it onto the lid. Not ideal but I should have planned ahead. The Cat 5 multicore feeds the lines to an external connector box and thence to each phone.

So by and large that concludes the project. At some point I'll create another blog that shows the exchange being used with a focus on the Plan 7, hopefully with some videos, but for now it's so long and thanks for all fish.

The End.