I have a SIM800c module with the following sequence of pins:
Top side: 5v, V_TTL, GND, TXD, RXD, DTR, SPKP, SPKN
Bottom side: MICN, MICP, Ri, VRTC, GND, PWR, GND, VBAT
The vendor told me that the module already comes with an internal antena, but it also has a connector for another external one. So I decided do not purchase the extra antena, and now I wondering if this can affect the behaviour of SIM800c.
The module is being powered from an external 12V power supply connected to a step down module lm2596 adjusted to give the 4V required by SIM800c. I also use the capacitors and the zener diode as recommended in the module datasheet. The power supply is connected to the 5V pin, and when I turn on the circuit a red LED light up indicating the the power is on, but no blinking LED appears on the module.
Before trying things that can damage my module, I would be very happy if someone could help me to answer the following questions:
- Can I power the module with 5v through the 5v pin, instead of 4v? I want to trying this because I’m getting around 2,74 in the VBAT pin, when I power the module with 4v. I also ask to myself why there is a 5v pin in the module since the maximum voltage recomended to SIM800c is 4.4v.
- Can I power the module through the VBAT pin, using the same power supply or a 9v Ni-Mg battery + step down, instead of the Li battery recommended in the datasheet?
- Should I use an external antena as well?
Thanks in advance.