Am 26.02.2014 um 19:07 schrieb Michael Mrozek:
Am Wed, 26 Feb 2014 17:53:24 +0100 hat "Dr. H. Nikolaus Schaller" hns@goldelico.com geschrieben:
- UMTS module activity sensor
Some people would like to reliably disenable the UMTS module because they don't trust the power-off command or the power indicator LED provided by the module. So they want some external mechanical switch
- or alternatively an activity indicator LED that uses external
hardware to monitor the module's power drain. This can quite easily be done (there are current sensor chips with a threshold that can make an LED illuminate as soon as the module draws more than let's say 5 or 50mA). One minor problem is that such a circuit adds a voltage drop which must be kept very small since the module may draw 2-3 Amperes from the battery during transmission peaks. A mechanical switch must also have a very low resistance and should be very reliable.
Be careful about a switch! We do NOT want to add a physical switch somewhere at the case! Not all units will have UMTS, and a switch adds costs (more complicated case mold, needs to manually be assembled, etc.)
Exactly - if we even get a switch that does not harm normal operation (2-3A switching current and less than 30 mOhms or so...). A simple DIP switch is definitively not reliable enough.
So in case an LED does not work, we will not include anything else - I still think the chance of the module being compromised is very very slim.
Me too... Those manufacturers have no interest in adding what some of our customers suspect. Because they can't risk ruining their reputation.
And would NSA be interested in tracking if a coke vending machine becomes empty? I don't think so...
But sometimes by thinking a little more we can find a good solution that makes everybody happy.
BR, Nikolaus