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gsm modem restarted while OUTPUT will turn ON/OFF.

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Junior Member level 2
Sep 19, 2014
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Tirupur, India
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hi friends,

in my project gsm modem SIM900A is interfaced with microcontroller.
in my project controller is used for turn ON/OFF the motor and prevent the motor from overload and dryrun current.

motor can ON/OFF by using GSM/manually. send current status of the motor.

MY PROBLEM is while turn OFF the pump either dryrun pump ,overload or manually the modem will restarted but controller works properly ,

i checked the power variations with the help of Oscilloscope. there is no variations in power.

so please tell me the solutions to this problem.

use ground isolation for gsm and motor power supply, if it is common.And use relay protection circuit for proper operation.just for debugging test hardware with two separate power supply one for GSM and other for motor.

If gsm connected through TTL with controller then you can use opto for rx,tx and gnd.

i already did it everything as you said expect opto to rx,tx.

i use 240v/12v-1A transformer for my ckt pic , gsm , relay and ds1307 are used with same pwr supply.

for gsm 3.92v passed, for pic &ds1307 takes 4.92v ,relay takes 12.01v.

i check gsm pwr supply Using CRO when Motor off condition they voltage will get slight down and quickly it will back normal.

if there is any problems in pwr. Tell me the solutions.

GSM works normal with out any interrupt but while turn OFF the motor it will restarted. why?

Motor will turn off through protective relay.

it will works sometimes properly ie 3:10.

that my confusion.

note: +csq: 21,0

Do you have a flyback diode with the relay?:

Your modem has the decoupling capacitors?
Your microcontroller has the decoupling capacitor?


Now i changed 1 amps into 2 amps circuit.
Yes i put 1n4007 Diode for relay circuit. yes i use 1000uf and 470uf 25v for microcontroller and three 470uf cap connected for gsm modem.

but same problem is occurred.

i change the decoupling capacitors 470uF into 1000uF .

after that i check the ps of modem as same voltage 4.13v, when i check with sim card vcc @ normal condition 2.8v~2.9v, at restart condition the gsm ps is same, but Simcard vcc is down fully after few seconds it will come back to 2.9v,

note:- csq is 22,0 with antenna,csq is 15,0 with out antenna

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