Portable Computers

[kellys_eye]

Years ago, portable computers were called PDA's (Personal Digital Assistants) and the best you could get was, by today's comparative market, very poorly powered and had a screen of VGA quality at best.

I realise that mobile phones have taken their place (let's not discuss tablet PCs here - bear with me) and their power and capabilities are astonishing considering their size etc.

If I wanted to go 'old school' and revert to a PDA-type device along the lines of a mobile phone, what would I need to do to that mobile phone to make it 'dumb enough'?

Disabling the phone part might (some say) be as simple as not fitting the SIM card but others would argue that your phone could still (theoretically) be accessed by interested parties even without one i.e. I can still make an emergency call without a SIM fitted so the 2-way comms is still (always?) active.

So what is necessary to actually, fully and completely stop (ruin) a mobile phones telecomms facility? I have a couple of redundant phones (an old Samsung G360 and a new-but-not-required Sony Experia L3) that would make brilliant PDA's but I would prefer to do so in the full knowledge that access to it is by MY design (whether or not I use wi-fi) and not leave it to indiscriminate SIM card access. Plus extend the battery life of course

 

[Nanren888]

Remove the probably surface mount antenna? (and match output to load?)
Some may have more than one.
Do you want to disable bluetooth and Wifi as well?

 

[DHR]

I'm not an expert , so I'm going out on a limb here, but could you disable all the com devices on the phone by disabling their drivers if you have root access? At least then you have the ability activate them later again if you decide you want to. Another simple solution might be to use Airplane Mode. Is that not a complete shutdown of com devices on the phone? If you disable WiFi, BT, NFC, GPS and enable Airplane mode, I don't think your phone will be able to send or receive any signals... could be wrong or missing the spirit of the exercise.

 

[Nanren888]

Is NFC enabled in airplane mode?
Just interested. Maybe NFC is not a concern to you?
If recent, UWB maybe also.

 

[DHR]

It might depend on the device. On my phone (Galaxy S10 Plus), I can turn airplane mode on, and WiFi and BT turn off but I can turn them back on without disabling Airplane Mode. Airplanes have WiFi services onboard now, which is probably why this phone does that but my old phone didn't. GPS and NFC stay active unless I turn them off. I believe that's because GPS doesn't broadcast, and NFC is such a weak signal that it doesn't matter either.

I had never heard of UWB before... Sounds cool... gonna have to get me some of that.

 

[Nanren888]

Confirm GPS is receive only & only location & time signals.
NFC is powered from the reader, the other end, so won't come up unless very close, as it's designed.
If new enough to have UWB, it'll act rather like bluetooth.
.

 

[kellys_eye]

The only comms I want to fully disable is the phone side. I have reservations on the software being able to do that - same goes with just removing the SIM card - and certainly 'airplane' mode won't cut it.

Even removing the antenna isn't good enough - you can probably still operate the device as a phone if close enough to a cell given how little signal it needs for normal operation - the antenna has very little gain so the system must rely on sensitivity.

I thought of shrouding it to block all signals but that stops wifi and BT which would still be required as a portable PC - I know that both those systems can be disabled in software (and can monitor the signals to prove it) but this isn't the same as the 4G/5G systems which, AFAIAA could well be operation 'when my back is turned'....

If this all sounds like paranoia then.... meh.... let it be. But the bottom line is that I'm not even sure if the manufacturers link cell operation into 'computer' operation in that disabling the phone side MIGHT disable its other functionality? The brute force method would be to 'stick a screwdriver in the cell phone part' but that's just being silly! As a metaphor, perhaps, BUT it's probably perfectly feasible in a genuine scenario if you knew which plug to pull.

On that bit, does anyone know if schematics are available for these phones (the Xperia in particular as its spec is somewhat better than the Samsung but a schematic of either would help - a lot).