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Unable to connet sim548c to hyperterminal

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omar.nasir123

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96910408001309626246.jpgHi,
I am using sim548c module using the schematic included. My problem is that when i connect sim548c with a serial cable to my pc, i am unable to send at commands through the hyperterminal. infact, the only thing displayed in the hyperterminal is "normal power down". i am manually pulling low the pwrkey of module. there is no RDY result displayed. however when i pull the pwrkey low a second time, it shows "normal power down". can anybody suggest me the solution? im using 115200 baud rate.
 
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There may be problem in powerkey. Transistor switching time can be a problem. 1st remove transistor and use manual button to switch on the module. 2nd check the power supply.
 

i did use manual button. the power supply is steady and within range. when i press the button once to pull low the pwrkey (around 3-5 seconds), it doesnt display anything. When i repeat the process i get the reply NORMAL POWER DOWN.
 

I had seen your circuit but I am not able to see the transrecivers in Rx and Tx lines.....if it is present then there is no problem .....but if it is not put MAX232 transreceiver in circuit.....there does level shifting of UART signals....

Good Luck
 

im sorry i forgot to include that part of the circuit in the schematic. i am using max 232 level converter. the rts and cts pins of the module are ground. does that affect the operation of the module?
 

You keep them floating ( do not connect them any where)..... generally with communcation with PC you only need RX TX and GND connection.... Also in hyper teminal you make no hardware flow control configuration.... Should work....

Good Luck
 

in order to communicate between microcontroller and other devices(Cell phone, PC and other serial devices) you must use Line driver/convertors such as MAX232 or MAX233.

 

When i pull low the pwrkey for >2s i get "normal power down" on hyperterminal but when i again pull it low i dont get the "RDY" message. please help me. kindly tell me what can be the reason. :(
 

Do not use MAX232.

Use MAX3232 instead. Ideally sim548c works on 2.8v TTL, compatible with 3.3v TTL.

MAX232 is R232 to 5v TTL driver, maybe that's why sim548c gets stressed out and goes into power-down automatically.
 

    V

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Thank you for your help s_guria.I am facing another problem that voltages at SIM holder terminals are fluctuating and status pin of the SIM548C module also gets low and high.But when we disconnect the SIM,the voltages at the SIM holder terminals get to zero value and status pin get stable and accept at commands hat do not require the network.
 

In simcom module STATUS pin is indicator of power-on state. STATUS pin is high as long the gsm module is in power-on state, never fluctuates.

omar.nasir123 said:
But when we disconnect the SIM,the voltages at the SIM holder terminals get to zero value and status pin get stable and accept at commands hat do not require the network.
Click to expand...

In your case, it seems like power supply is not capable of delivering enough current during network activity. when you remove sim there is no RF activity, so everything seems to be stable.
simcom says module can draws peak of 2A current during rf-tx (and it really does) burst.

make sure your power supply is capable of supplying minimum of 2A.

you may use regular cellphone battery (Li-ion only). And connect 5v at VCHG pin, sim548c has built in Li-ion charge controller.

goodluck
 

    V

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Thank you, the problem was with insufficient current through the power supply.
Can anyone tell me does this module support TLS ?
 
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so any ideas how to send email through gprs using sim 548c?!
 

okay i will post futher queries on the second thread you mentioned. Thanks a lot, the power issue has been resolved.
 

Hi:sad:

I can receive any thing in port COM1 ? i have a schematic like up , STATUS pin some time is 1.3v , 2.9v or 0.03v .
i have 3.9v stable for VBAT and 5v for max232 .
I thing it is power up correctly and power down too , but i can not connect to serial port . help plz

I not connect sim card yet . can it makes the problem ?
plz help me
 

oh my ***
some time it work and some times not ????????????????
i use max232 - usb for 5v and another power suply for 3.5v and some time i get all data good and some time it not work ???
every one knows the problem ?
 

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