[AVR] i have a problem in a gsm based atmega16 project

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balvendrajat

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i am using a gsm based project for controlling a device in which i using 9v/ 1000MA adapter for gsm sim300 and 5v/750MA power supply for controller and other component. but it is not working properly (some times works but some time not). and my code is correct.
so what can i do and please tell me the proper current rating
 

I suspect that in transmission mode, the current drawn by the SIM module is so high that the supply voltage of your system drops below the treshold voltage of your microcontroller, thus resetting the circuit.

You can verify this hypothesis by powering the SIM module from a workbench power supply, if that solves the problem then your power path needs some adjustments. I'd recommend adding several large caps (i.e. a few mF) in parallel with the SIM module's power pins to provide a higher current in transmission mode.
 

milan.rajik said:
While sending SMS SIM900 draws 1 to 1.5A current.
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Thats about twice the maximum rating of your 5V regulator, so I would suggest the following dual solution:
- Swap your current 750 mA voltage regulator for a switched mode version like the LM2596 with a maximum current of 3A.
- Add 2 capacitors of 2200 µF (rated at 16V) in parallel over the SIM module supply pins. Normally they won't be necessary though, as your adapter can supply 9 W of power and the SIM module only consumes 7.5 W but of course I don't know about the rest of your circuit.
 

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