connecting cellphone using rs232 circuit

Discussion in 'Embedded Systems and Microcontrollers' started by cakrawibawa, Apr 2, 2009.

  1. cakrawibawa

    Thread Starter New Member

    Mar 18, 2009
    Dear All,

    I wanna connecting my Handphone to my computer using RS232 (Com1 or Com2).

    This hp (handphone) have 4 pin: Gnd, TX, Rx and Vbat

    Gnd and Vbat for charging the battery

    Gnd RX and Tx for data communication.

    The microprocessor is QualComm QSC6010

    Voltage and current level is...
    Gnd - Tx = 2.8V, 7mA

    I have succesfully connecting this handphone using a Nokia DKU-5 data cable.
    Tx from cable going to phone Rx.
    Rx on cable receive signal from phone Tx.

    In last few days, I got many failure using the DKU-5 cable. My handphone cannot connect to the computer. After do some investigation, I get one which work. Using DKU-5 (Prolific PL2303 chip) I measuring the voltage and current level output which work is between Gnd - Tx = 3.7V, 35mA.

    I try creating two circuit as the DKU5 cable substitute. One RS232 to TTL using Maxim Max232 IC, and one again using BC547 and BC557 transistor. Since the voltage output from Max232 and transistor is 5V, I cannot connecting directly to my handphone.

    Then, I try add a resistor as voltage limiter (Three 10K resistor in a series, between output and Gnd). I get 3.3V, but my handphone still cannot be identified by the software.

    Do you have any ideas to make my handphone can be connected ?
    Any circuit which you advice for me to use?

    Add info:
    1). Current output from Max232 IC and the transistor circuit only 5mA. Is this cause why my handphone cannot be identified?

    2). I don't want to use PL2303 from prolific or ARK chip from ARK Micro. I don't have skill in SMD/SMT component. That's why I create circuit using transistor and Maxim Max232.

    Thanks for your ideas.