Cannot start SIM900a by software ? Is that the P, DT or DR pin

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philgib

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I just cannot find it on the doc... I understand that if I connect arduino to SIM900 "P" pin, it should be able to pwr on or pwr off. But nothing... Should I use DT or DR instead ?

I have from left to right the following pins :
RST P Tx Rx DT DR - +

Thank you
 

@Philgib,

Pls share the schematic, that how you have connected the Microcontroller and the SIM900A.
 

@Philgib,

As per the attachment, you are giving power supply to the SIM900 from arduino board. But in order to start the SIM900 modem you can do it either having a simple circuitry or control the ON/OFF of SIM900 using a digital pin from MCU...

The PWRKEY pin og SIM900 has to be controlled through the MCU...If the power supply is given from the arduino board pls check the VDD_EXT pin of the SIM900.
 

In your diagram the SIM900 is powered from 5 volts, this is wrong as the maximum supply voltage for the SIM900 is 4.8 volts.

The SIM900 WILL NOT start if the maximum supply voltage is exceeded.

With the SIM900 supplied by the correct voltage and the power supply can provide adequate current (2 amp peaks) the SIM900 is started by pulling the PWRKEY line low for > 500mS.

The PWRKEY line must be driven low by an open Drain/Collector output.

Also note that the TX/RX pins on the SIM900 are at 2.85 volts so level translation is required to connect it to the Arduino.

Cheers
 

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