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SIM900 automatic power-up

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logicnibble

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Hi!

I would like to make the SIM900 module to power-up automatically after receiving power supply.
The Hardware Design datasheet mentions that it is needed to pull PWRKEY pin to GND or to PWRKEY_OUTPUT pin for more than 1s via a transistor or a pushbutton.
I want the module to be able to resume operation after a mains failure (and back up again) without human intervention. And I'm using the SIM900 standalone with no uC.

Do you have any ideas how to do it or Have you used the SIM900 module in this way?

Thanks!
 

Maybe a RC power-on-reset type circuit solve your problem. But your another problem is to achieve a 1 secons long "logical low" state signal.
por.gif
**broken link removed**
 

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Program your microcontroller to do the job. use STATUS pin to check module ON/OFF state.
 

Hi crackerboy,
Ok it's my bad, but still in my opinion using cheap micro is the best solution, because SIMCOM says at "least" 1s long logic low has to be applied to PWRKEY. Practically you have to make sure that it actually turned on or not, module also takes some time to boot after applying power on logic. In real life sometimes power on process in not successful.
using discrete components will not be reliable.
 

Hi,

Has anyone of the exprecienced SIM900 users fixed or solved the issue that there is no option for auto powering-up the module when is supplied with a supply voltage?...

Isn't there any hardware or software solution aside using a small microcontroller for generate the powerkey signal after module power-up process?...

regards,
Ignacio
 

logicnibble said:
Hi!

I would like to make the SIM900 module to power-up automatically after receiving power supply.
The Hardware Design datasheet mentions that it is needed to pull PWRKEY pin to GND or to PWRKEY_OUTPUT pin for more than 1s via a transistor or a pushbutton.
I want the module to be able to resume operation after a mains failure (and back up again) without human intervention. And I'm using the SIM900 standalone with no uC.

Do you have any ideas how to do it or Have you used the SIM900 module in this way?

Thanks!
Click to expand...

Check this:
Connect Sim900 PWRKEY pin with a diode to the VBAT pin.

This way:
PWRKEY -----|>|------ VBAT

Also place a 470uF cap between the PWRKEY and GND.

This will work!
 
Last edited:
logicnibble said:
Hi!

I would like to make the SIM900 module to power-up automatically after receiving power supply.
The Hardware Design datasheet mentions that it is needed to pull PWRKEY pin to GND or to PWRKEY_OUTPUT pin for more than 1s via a transistor or a pushbutton.
I want the module to be able to resume operation after a mains failure (and back up again) without human intervention. And I'm using the SIM900 standalone with no uC.

Do you have any ideas how to do it or Have you used the SIM900 module in this way?

Thanks!
Click to expand...


Place an appropriate capacitor between PKEY and GND. As far as I remember, 10uF worked fine for me. Works like a charm.
 

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