5 ms·
> You probably shouldn't leave a sensitive device unattended anyway I find this area fascinating in terms of how you protect devices that are both sensitive, a
by jon-wood 6y ago
> You probably shouldn't leave a sensitive device unattended anyway
I find this area fascinating in terms of how you protect devices that are both sensitive, and need to be left unattended in someone else's possession. One of the best explorations I've seen of this is Big Clive's tear down of a smart meter. The thing is absolutely full of anti-tampering measures, including several switches that will cut off the power supply if the casing is removed, but most interestingly to me the cellular modem being connected to a big capacitor designed to give it just enough power to send out a last cry for help even if the entire radio module is pulled off the meter.
https://www.youtube.com/watch?v=G32NYQpvy8Q https://www.youtube.com/watch?v=G32NYQpvy8Q
- implements 6y agoThe capacitors may just be part of the standard power supply circuit for the mobile telephone modem. I looked at the SIM800 module a few months ago - people use them to add mobile connectivity to embedded hardware like Arduino. The module is designed with a 4v LiPo battery in mind as it can draw 2 amps for a few milliseconds when transmitting, so needs a buck converter and hefty capacitors rather than the usual linear voltage regulator. NB: Not a hardware engineer - was just interested in adding SMS notification to my home alarm.
- BoorishBears 6y agoThe modem actively broadcasts the removal, it's a very intentional design choice
- jjoonathan 6y agoThe big capacitors are mostly for outage detection, not doofus detection. However, the number of doofuses they help detect is not 0.