I've just obtained a (circa 1992) Sony CM-H333 mobile phone, commonly known in the UK as the 'Mars Bar' owing to its size and shape. Like so many early mobile phones, it was made obsolete in the early 2000s when the 1G (ETACS) phone network was shut down in the UK.
I plan to replace the phone's now-useless RF board with a Bluetooth module (following an unsuccessful attempt with a SIM800L GSM module). This will, theoretically, allow it to be used to receive and/or make phone calls again, with the help of a modern device.
A little while ago, I got hold of a SIM800L module and tried to install it in the phone, powered off a 4V supply line from the CM-H333 PCB and...it didn't work. Although the phone was definitely supplying 4V to the module, no flashing lights appeared on the SIM800L.
I suspect the current from this supply line is insufficient to power the (rather current-hungry) GSM module. I think I'll try a different tack - installing a Bluetooth module instead. Although the purist in me would have preferred to get 2G connectivity to the handset (thus resurrecting it as a proper phone) I am happy to settle for shapeshifting the phone into a Bluetooth headset.
The Bluetooth module I'm looking at is the JDY-64 as this includes a microphone input (quite rare among the myriad DIY Bluetooth audio modules on eBay) and it should run off the 4V supply line, requiring a far lower current than the SIM800. Fingers crossed!
One of the joys of buying old mobile phones is that they tend to come with free biohazards, courtesy of their rapidly-decaying NiCad batteries. This one was no exception.
Once I prised open the battery casing (wearing gloves!) I quickly removed the gunky old NiCads and wrapped them in kitchen roll, ready for disposal. Actually, they weren't too badly decayed, given that they probably haven't been charged since the Millennium.
There was more good news. Before buying this phone, I knew that the CM-H333 battery pack is rated at 4.8V. This sounded like code for 'probably just 4 AA rechargeable batteries in a box' and it turns out I was right. All I needed to do was insert a battery contact at one end of the prised-apart battery box, tidy up the main terminals to ensure they made proper contact with the phone's +/- pins (with a bit of very carefully positioned tin-foil) and put the two halves of the battery pack back together.
Huzzah! I now have a 2,450mAh Ni-MH battery pack for the old Sony, containing nearly-new batteries.
My Sony Mars Bar has arrived, so before I start chronicling my attempts to modernise it, I just thought I'd warble on about the phone's history a bit.
1992 was probably the year when mobile phones first came within the reach of the ordinary UK consumer for private use. Of course, mobile phones had been around since the mid-1980s for the obscenely rich, the business user and the obscenely rich business user (of whom there were quite a few in the late '80s). However, not many ordinary folk would have been in a position to buy one - they weren't yet 'high-street' items, the costs were astronomical and, with payphones far more commonplace than they are now, why would you have needed one anyway?
Then, in 1992/93, three things happened in quick succession:
(1) Cellnet (now O2) launched their (relatively!) affordable Lifetime tariff, which was aimed at low-frequency users. The marketing pushed the idea of an 'emergency' phone for peace-of-mind, probably spending most of its life tucked away in your car glovebox. (I think Vodafone launched something similar as well - LowCall?)
(2) A new crop of easy-to-use mobiles aimed at the novice user went on sale. As wellas the Sony CM-H333, there was the cheaper (and famously screen-less) Motorola Personal Phone. The Nokia 100 followed soon after.
(3) Said phones started becoming readily available in High Street stores. The CM-H333 has the honour of being the first mobile phone to appear for sale in an Argos catalogue - £325 (on contract!!) in the Spring/Summer 1993 edition, on Cellnet Lifetime.
The phone itself is surprisingly small for its age - it's narrower than my 'real' phone (a Nokia 105) and very light. Feature-wise, you get 9 number memories, 3 extra speed dials, adjustable ringer/earpiece volume, a snazzy pop-up earpiece that can be used to answer calls (seven years before the Nokia 7110 made slidy bits fashionable) and a call timer. Oh, and a wrist strap. I wish all phones came with wrist straps - they're so sensible.
My particular handset is functioning, and would have been on the Vodafone network judging by the '0374' dialling code on the label on the back. Sadly, it isn't in great physical condition - but this doesn't bother me much, as it'll get knocked about a bit anyway over the course of the project, and I wouldn't want to ruin a museum piece with a stray soldering iron tip. If the project works, I might search out a more 'pristine' example and do a circuit-board swap. It'd be nice to get hold of the original battery charger as well.
Did I mention batteries? More on this very soon...(let's get the gloves ready).