|Doug's SxS Switch|
Jan 2005 - Jan 2008
|The proposal is based around the Linux-based Asterisk open source PBX, so I have been working on the configuration of a computer to run Linux and then load up and compile the Asterisk software. So far I have had some problems with the version of Linux I tried since it appears to not include all the modules needed to successfully compile the PBX software. At this writing I am downloading a later version of Linux to try. I was successful, however, in finding on eBay a very affordable trunk card for the Asterisk PBX and have it already in hand. I still need a station card and I am on the lookout for one of those, too.|
10 February 2005 -- A nasty water main break over near work has work closed today so I took the opportunity of "found time" to neaten up the
Asterisk PBX installation and its connections to the step switch. First, I mounted the Sipura ATA box and Mitel Smart-1 dialer unit behind
my computer desk, pictured at left. The Sipura SPA-2000 is the small gray box, and the Mitel Smart-1 dialer is the black box to the left. These
items could actually be mounted just about anywhere, including near the switch, but my thinking is to
keep all the computer-related stuff by my main computer and Internet and network connections. Wiring behind the computer desk was connected to the outgoing trunks
on the switch as well as a step switch station line.|
The Asterisk PBX machine was placed next to my computer desk and hooked into the network and the step switch line for the incoming calls. The machine is pictured at right and has an old WE500 sitting atop it which is plugged into one of the outgoing FXS ports on the Sipura ATA. It is my "console" telephone of sorts to be able to test outgoing VoIP calls.
|19 February 2005 -- Worked out a vexing problem with the step switch and VoIP interfaces. I had a weird problem where
if I used DTMF ("Touch Tone") to dial out on a VoIP trunk, the switches would perform correctly but drop the connection as soon as it selected
the trunk into the VoIP ATA, as if the calling station had hung up, which it hadn't. The line finder, seeing the station off-hook, would jump to life again and
search for the line and return dial tone from the first selector again. Sometimes dialing the VoIP trunk again would result in the selector successfully seizing a
VoIP trunk, and sometimes it wouldn't. If I used a rotary phone, everything worked fine. After trying different variables in the equation I finally came to the
conclusion that the holding bridge on the DTMF-to-pulse converter on the switch paths was loading down the line to the VoIP box too much so that there
wasn't enough current for the "A" relay in the selector to hold the switch train. The solution, or at least a work-around, was to wire the trunks to
the Sipura box over at the second-to-last and last terminals on the "1" level so that by the time the selector hunts/rotates over there the holding
bridge in the DTMF/pulse converter had dropped out. That holding time isn't adjustable, unfortunately, and a better solution would be more current
available from the Sipura box, but that isn't adjustable, either. However the problem has been worked around and now DTMF stations can dial out successfully
Pictured at left is the rear sleeve & line termination panel on the switch and the VoIP trunk board is on the left edge, just above the small punch block and screw terminal blocks.
|5 April -- Finished wiring in the last plate of line & cutoff relays. Yesterday the plate was bolted to the switch frame and the first ten lines' worth of relays was connected and then tonight the last ten were hooked up. There are now 80 dialable stations on the switch. One line has a broken line relay, but that line has been permanently busied out so that folks dialing in from the CNET have a busy line to dial to so the busy tone can be heard. It is most gratifying to have a significant portion of the switch now built. Things on the yet-to-do list include a release battery alarm, all circuits busy tone, and quite possibly hooking up the reverting ring selector I have.|
|5 May 2007 -- Received an interesting package from a web page reader this week -- thanks, Paul!! I am in possession of a
small shelf section with some switches, namely a selector, two outgoing repeating trunk plates, and a connector. Apparently in a previous
life this was a demo switch of some kind. I have been wanting to assemble a portable demonstration switch for some time now and this will make
the perfect base for just that sort of switch. The shelf section will hold up to four switches or other apparatus.|
The thinking at the moment is to configure the demo switch with a line finder, a selector and a connector, perhaps using a party line connector (I have a couple in stock!), which could increase the number of lines that could be configured.
Some planning in the engineering of the switch will be needed to connectorize everything so that the switches can be easily installed or removed from the frame to transport it because this old switch stuff is pretty heavy. The unit as pictured weighs in excess of 70 lbs.