Felix wrote: > My only doubt is about powering all through a resistante > when you put the button in off state, what's the result? current limitation > or lower voltage?
One purpose of the power switch (SW2) is to prevent a device with compromised or defective firmware from doing anything without the user knowing. Unwanted activities would mainly involve RF, with the assumption that there is a "secure perimeter" where you're basically safe (your home, office, underground bunker, the desert, etc.), and the potentially hostile rest of the world. Undesired activities would include: - broadcasting secrets, - alerting listeners of your presence, - profiling (e.g., by recording RF signals ... think WLAN geolocation and such. The transceiver could also monitor the activity of your 2.4 GHz networks even though it could only decode their data if they're IEEE 802.15.4.) A compromised device could do such things actively, but also a mere bug could make the device do things that could be exploited. All this is of course ineffective against someone modifying your hardware. But that's a different class of attacks. The idea behind R9 is that you can only draw a few uA or your supply will collapse down to useless voltage levels. This limit should be high enough to survive in a deep sleep mode but too low to do anything but sleep. Especially RF should be impossible to run if power only comes through R9. This small standby supply is needed to allow the device to run its real-time clock even when switched off. It also has the silo capacitor C15 (inrush current-limited through R5), but that is designed to keep it alive only for a few seconds, e.g., when swapping batteries, not for what may be days when switched off. - Werner _______________________________________________ Qi Hardware Discussion List Mail to list (members only): [email protected] Subscribe or Unsubscribe: http://lists.en.qi-hardware.com/mailman/listinfo/discussion
