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The 802.11 SIP/Coinless Phone

This all started when I spotted one of these ugly things at a local swap meet, sitting disused in a box. The guy only wanted $10 for it, said it didn’t work. I figured, worst case scenario was that it did in fact not work and it just needed a little TLC to make it working again. I handed over $10 and walked away with it.

So, it’s been sitting around in my junk pile for a while. I finally got around to fiddling around with it. Sure enough, I plugged it in to a Grandstream ATA, picked up the handset, and it worked. “Hot damn,” I said. I was the proud (?) owner of a working phone, yee hah.

I got to thinking about how nifty it would be to have a phone that could be kinda “left out back” for social gatherings and the like, without me having to worry about the weather, abuse, and who knows what else. A little fishing around in my junk, and I discovered that I had a Netgear wireless bridge and a Grandstream ATA.. that once removed from the case would fit inside the phone.

Off to the hardware store I went to purchase some cheap Lexan, an assortment of wiring fiddly-bits, and everything I needed to make this.

As you can see from the picture, the phone itself is a strong steel case with a payphone-style dialpad, handset, and hook switch. Typically,
these devices are designed to withstand darn near everything you can throw at them. This one is no exception.

The insides are quite spartan. A simple circuit board, some configuration jumpers (which I’m not quite sure exactly what they do) and some places to connect telephone spade lugs. I assume that this board is actually designed to go into a COCOT phone or similar, and that the spade lug connectors are designed to connect to various other things that a COCOT phone would need.

Anyway, the phone part was real easy. Just a simple modular cord was all that I needed to make it happen.

As I started assembling all the pieces of this project, I realized that I got real lucky. The Netgear wireless bridge I have has the antenna connected on a pigtail.. so I could simply drill a 7/16″ hole in the side of the case and mount the antenna on the outside! While not nearly as waterproof as I’d like, it will do nicely.

As the day wore on, I started wiring things up. The first thing was to kind-of dry-fit the 802.11 bridge and the ATA circuit boards to the plastic “backplane”. I had to try a couple of different configurations before I got one that worked, and I used some double-sided sticky tape to secure the boards down to the Lexan.

Another way I lucked out was that both devices needed only 5VDC to be powered, and that the phone itself seemed to be able to operate 100% from phone “battery”, making the “how do I power everything” step real simple. A bundle of AA batteries and a 7805 voltage regulator solved the power problem quickly.

It all went together pretty quickly. By late afternoon, I had the whole kit wired up and ready to go.

In action, it works about as well as you would expect. I have a good 802.11g network, with pretty good signal strength throughout my entire house. I’m also connecting to a local Asterisk box, so that helps a lot as well. When I first started this project, I was a bit concerned that the metal case might present a problem for the 2.4GHz radio.. but it seems to be none the worse.

Going forward, there’s a lot of “improvements” I’d like to make right off the bat. First off, the 4 AA NiMH batteries don’t QUITE provide enough oompah to make this phone really last for very long. There’s plenty of room in the bottom of the phone, so I think the first major improvement is going to be a 6V gel cell alarm battery and a charging circuit.

Another thing that would be “cute” is to have the LED status lights for the bridge and the ATA to be visible, so you can see at a glance if anything’s not working. Along those same lines, since the phone has no ringer, an electronic ringer would probably also be a good addition.

I’ll probably eventually write a lot more. I suspect that this is just the beginnings of me playing with this cool toy. I know right away that I’m going to try to see if I can find a real pay phone pedestal to mount this thing on.. and maybe a matching round “Phone” sign as well.