Electrical – SIM900 Circuit Design. Where to connect PWRKEY of SIM900.

gsmsim900

I am designing a circuit for SIM900 with a MCU. I have never designed the circuit for SIM900 so thought of posting question so that someone can review it.
As per the datasheet, SIM900 works on power between 3.2v-4.8v. For this I have used LM317 with 150 & 370 resistors. So it will give output voltage of 4.33v. Below is the schematic for it:

enter image description here

VBAT is the output voltage of 4.33v.

Now in SIM900 I have connected TX RX pin to the MCU and have made connection for status and netlight, SIM Card connector. I have connected VBAT and GND. But I am confused with PWRKEY connections. Below is the schematic :

enter image description here

I don't have an idea about PWRKEY. I have a GSM Module and they are using a switch button for it which when pressed connect it to ground. But I do not want this. Is there any alternative for this. Also please review my circuit. Thanks.!

Best Answer

  1. LM317 is not a good candidate for this project,use LM2576 & LM2596 adjustable voltage regulators
  2. check UART level between your host controller(MCU or ...) & Module,if they operate in the different level you need a level shifter buffer.
  3. PWR KEY used for turning module ON/OFF,for doing this you must pulled it down for a moment(less than 500 ms or around)
  4. Read simcom's app notes and reference manual & datasheet,all above described there in detail.
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