amphichon

Project summary

Our goal is to convert an old cell phone to work with an intercom-type security system for keyless entry. We’re going to do this as simply and inexpensively as possible.

Plan outline

• Set up an old cell phone with a SIM card to use prepaid minutes
• Analyse the phone’s electronics to identify a point at which we can intercept the “ring” or “vibrate” signal and use it externally
• Analyse the intercom system’s electronics to set up a parallel switch for the remote entry button
• Interface the phone signal with the intercom’s remote entry switch

13 August 2005 – Setting up the phone

I started out by making a few calls. My current cell is with T-Mobile, so while I’m not particularly impressed with them, I figured I’d give them a chance to participate in the experiment. Called their support folks and asked about how I would go about getting an old cell phone set up with a prepaid SIM. After shuffling me around to a few people and leaving me on hold for several minutes, they disconnected me. (Note to self – look for a new cell provider.) Next I tried Cingular, mainly because my old Nokias were with AT&T and since Cingular bought them out, I figured they’d be best positioned to help me with these phones. A quick call to the local Cingular store yielded some good information – yes, they provide prepaid service, and in fact, if I walk in with an unlocked phone, they’ll put a prepaid SIM in it for free. So far so good. Unfortunately they were closing soon, so I figured I’d take stock of the phones I have and figure out which would be best suited for this project.

Here I immediately ran into a snag – Of the three Nokia stick phones I’ve got sitting here – the 5160, 6160 and 3360 – none of them appear to use SIM cards. Doh. Not even my last-before-current cell, an LX5150 from Sprint, uses a SIM card. My current phone, a Sony Ericsson T610, uses a SIM, but since I sort of depend on it right now (it’s my primary phone), it’s not really a candidate for disassembly. So for the moment it’s not clear whether any of these old phones can be recycled for this project. I’ll do a little more research and update once I know more.

7 September 2005 – Project on hold

As noted elsewhere, I’m working on a move to Portland at the moment, so this is on hold. I expect that in the new place we’ll be trying this (two geeks in one apartment for six months means there’ll be way too much experimenting going on, I expect). I did find a couple of suitable phones on eBay and put in bids but they got too expensive (probably all those other guys reading my page and eager to try this themselves, I’m sure) so I’ll just wait until I have a chance to hit the resale stores. Will update once this gets moving again.

5 August 2006 – Project continues to be lovingly held

The move to Portland did eventually happen, as most of you know. The entry system at the new apartment didn’t lend itself to this project though. It’s one of those phone deals where the visitor calls from the lobby through this built-in phone panel, which routes to your home or cell phone, and you press 9 to buzz open the door. I’ll likely be moving again within the next few months, and there’s a good chance I’ll find myself in one of the old-style apartment buildings, in which case I’ll resurrect this project. In the meantime though I’ve got a nice little workaround here – I just have the panel from downstairs routed to my cell phone, so I can call myself from the lobby and buzz myself in, if I forgot my keys. (Of course, if I forgot my keys, there’s a better than even chance that I forgot my cell phone as well. Doh.)

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