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I've been searching around google and even in manufacturer site for this information and found nothing relevant. Is it possible to turn off GSM module and keep turned on the GPS? How can it be done?
This point is critical to my application since I need to keep GSM module OFF almost all the time and the GPS always ON.
edit: Command manual and product page for Simcom SIM908.
[This started as a comment, but I ran out of room.]
Having the GPS on while GSM is off (or in a low power mode) may be possible. Look into the hardware design guide for SIM908 (4.2MB .doc). Section 4.3 describes the low power modes for GSM and how to enter them. Section 5.2 describes power control for the GPS.
Somebody who had first-hand experience with this module might be able to provide a more definitive answer. E-mailing a carefully crafted question to Simcom 's application support might also be a good idea. (And if they tell you the answer, make sure to post it here on EE.SE for posterity.)
There is no way you can turn off GSM while using GPS. As hardware manual say in section Section 5-GPS Application Interface
The GPS engine is controlled by GSM engine, so when it is necessary to run GPS, the GSM engine must be powered ON and not in SLEEP mode.
there is a method. But this is not formal or SIM recommended.
Inbetween the data signal of the sim card and the SIM908 simcard data input pin, insert a MOSFET which is controlled by your MCU. MOSFET must have not greater than 22 Ohms resistance.
When the mosfet is off, SIM908s' GSM engine will not consume as much as power it would, if it had access to the sim. Whenever you need GSM connectivity, then enable the SIM through the MOSFET.
hope this helps.
