Henry Kolesnik wrote:
I sure see lots of retired cell phones and wonder why I haven't seen any
homebrew projcts to make something useful out of old outdated ones.

It always surprises me how little useful I can get out of these. I
used half the diplexer from a big old one as a filter for an 875 MHz
local oscillator chain for a 903 MHz receiving converter. And I used
the speaker from a more modern one to provide sidetone for a laser MCW
transmitter. That's it so far....

73,
Steve VE3SMA

) writes:
Henry Kolesnik wrote:
I sure see lots of retired cell phones and wonder why I haven't seen any
homebrew projcts to make something useful out of old outdated ones.

It always surprises me how little useful I can get out of these. I
used half the diplexer from a big old one as a filter for an 875 MHz
local oscillator chain for a 903 MHz receiving converter. And I used
the speaker from a more modern one to provide sidetone for a laser MCW
transmitter. That's it so far....

The big clunky ones, and I've not seen any at garage sales in a few
years, have offered up things like FM IF strips (they've tended to
be really easy to isolate from the rest of the unit), various crystal
filters with centre frequencies above 30MHz which would be suitable
as roofing filters, some txcos, go back far enough and they have
standalone NE570 (or later variants) compander ICs. I've also pulled
prescaler ICs out of them.

The trick is that the older and bigger they are, the better the parts.
There will be recognizeable parts, and many will even be in DIP packages.

The more recent they are, the less valuable because everthing gets
highly integrated. I opened one hand held cellphone, of recent
vintage obviously, and the IF filter was barely recognizeable.

Because they were specifically designed to be part of a system (ie
you'll never use a cellphone by itself), they have usually been
way too dedicated to allow for much in the way of modification.

MIchael VE2BVW

Michael Black wrote:

) writes:
Henry Kolesnik wrote:
I sure see lots of retired cell phones and wonder why I haven't seen any
homebrew projcts to make something useful out of old outdated ones.

It always surprises me how little useful I can get out of these. I
used half the diplexer from a big old one as a filter for an 875 MHz
local oscillator chain for a 903 MHz receiving converter. And I used
the speaker from a more modern one to provide sidetone for a laser MCW
transmitter. That's it so far....

The big clunky ones, and I've not seen any at garage sales in a few
years, have offered up things like FM IF strips (they've tended to
be really easy to isolate from the rest of the unit), various crystal
filters with centre frequencies above 30MHz which would be suitable
as roofing filters, some txcos, go back far enough and they have
standalone NE570 (or later variants) compander ICs. I've also pulled
prescaler ICs out of them.

The trick is that the older and bigger they are, the better the parts.
There will be recognizeable parts, and many will even be in DIP packages.

The more recent they are, the less valuable because everthing gets
highly integrated. I opened one hand held cellphone, of recent
vintage obviously, and the IF filter was barely recognizeable.

Mostly the receivers are direct conversion or low-IF (hundreds of kHz) these
days, and the IF filters are active R-C filters on chip (then come the
ADCs, followed by a DSP channel filter).

If you find a phone which was built 3 or more years ago then you will
probably find a couple of quite high performance (good phase noise) Voltage
Controlled Oscillators on little PCBs in metal cans. These could be
re-used if the frequency is right for what you need (one will be in the
transmit band of the phone normally, and the other one might be at a
strange frequency). In phones from the last couple of years, those VCOs
are all on-chip.

In GSM phones more than a year old, there will very likely be a good quality
Temperature Compensated Voltage Controlled crystal Oscillator (TC-VCXO) at
either 13 or 26 MHz, and those have much better phase noise and tempco than
typical crystal oscillators in cans that you would get out of most other
consumer products. The control voltage provides an easy way to adjust it
(over a few PPM range only, e.g. calibrate it to a received frequency
standard, which is what the phone does). Now in new phones they are
starting to use on-chip oscillators with a separate crystal that would be
less useful to homebrewers as it is not inherently temperature-compensated
without the phone's software. It would still be a good crystal though, and
in many cases the specifications can be found for the crystal.

The PA is normally still a separate component, so if you want a watt or so
of RF then that component could quite likely be reused though they are
fairly narrow-band if you want the full performance.

Other things you might find are LNA chips and SAW filters (e.g. in 3G phones
you would find one at the Tx frequency and another at the RX frequency, in
Europe this is a 60 MHz bandwidth centred at 1950MHz or 2140MHz. This
might be useful as a first IF in some kind of up-converting architecture
like a spectrum analyser.

I have also seen some websites where they have figured out how to drive the
colour LCD panels out of recent phones for microcontroller projects.

Chris