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Somebody in the thread at some point said: | Setup: The GSM modem is registered to a network but otherwise idle. The | GTA02 is connected to a PC via USB, the battery is removed and instead | power is supplied by an external power supply. There is a 1 Ohm resistor in | one of the supply lines, the voltage across this resistor is measured. Only 1R is very high for this kind of measurement considering it's sucking |2A, you're dropping >2V here to definitely impact operation of the thing you're measuring --> | been clearly visible. One interesting thing: If the external power supply | limits the current, the GSM modem will perform a reset when trying to | send and there is not enough current available (probably the supply voltage | will drop and causes the reset). I am not sure what happens if the battery | is weak and if this could happen during normal operation. I think this is a very nice idea to get a grip on what this autonomous, current-sucking thing is doing. There's a great isolated Hall-effect integrated solution for current measurement that would enable monitoring at high bandwidth (80kHz) with much reduced impact on the voltage cheaply and simply: http://www.allegromicro.com/en/Products/Part_Numbers/0712/ http://uk.farnell.com/allegro-microsystems/acs712elctr-20a-t/sensor-current-20a-soic8-712/dp/1329624 You just replace your 1R resistor with it and give it 5V, hook the output to your scope. BTW it's a great relief to have someone dealing with the firmware :-) - -Andy -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org iEYEARECAAYFAkkwICwACgkQOjLpvpq7dMrL+gCeIgoxQDYl1m11XOPDa74oe0gz 4mcAn2LG7/O0DGxg04HsybJKC+7wtEg5 =aNms -----END PGP SIGNATURE----- _______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
