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Can CP2102 USB to UART be used to power 5V devices?

Discussion in 'General Electronics Discussion' started by ssc953, Jul 17, 2016.

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  1. ssc953

    ssc953

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    Jul 17, 2016
    I am using CP2102 based USB to UART converter board to interface my UART based radio modem with my PC.
    The radio modem works on 5V. I have made the following connections:
    Radio Vcc => Converter 5V pin
    Radio GND => Converter GND
    Radio Tx => Converter Rx
    Radio Rx => Converter Tx
    However, I am not able to establish communication. I have successfully installed the USB drivers. The CPU activity LED of the radio modem is also not blinking.
    Is it because CP2102 cannot drive 5V devices?
    or is something else wrong?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    1) What powers the converter board and how much current can it supply?

    2) what current is consumed by the converter board?

    3) what excess current can be supplied? (the difference of the above)

    4) how much current does the radio modern require?

    5) is the current required (5) less than or equal to that available (4)?
     
  3. ssc953

    ssc953

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    Jul 17, 2016
    1) The converter board is powered by the USB port of the PC. It can supply 500mA.

    2) Max current through Vcc and GND = 500mA
    Supply Current = 26mA

    3) Around 475mA

    4) Max current requirement of radio modem: 130mA

    5) Yes

    Current requirement seems to be fulfilled. Then why isn't the radio modem working?
     
  4. Kiwi

    Kiwi

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    Jan 28, 2013
    A USB2 port can only supply 500mA.

    I use a CP2102 board to program and test run Arduino Pro Mini boards and stand alone ATMEGA328P micros without any problems. Just have to limit the output current to keep it well below 500mA.

    Must learn to type faster.:)
     
  5. ssc953

    ssc953

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    Jul 17, 2016
    Thanks @Kiwi Did you power the Arduino with CP2102 board?
    i got confused after reading CP2102 datasheet. It shows 5V pin as power input pin. Can an input pin drive an external device?
     
  6. Kiwi

    Kiwi

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    Jan 28, 2013
    Yes, the CP2102 board was powering the Arduino.
    Here is a photo of the programming board I use.
    upload_2016-7-17_21-40-50.jpeg
     
  7. ssc953

    ssc953

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    Jul 17, 2016
    Thanks @Kiwi . Surely then power is not the problem.
    Any idea what could be going wrong in my circuit. Why the radio modem does not turn on?
    (I know that it will not turn on if Tx and Rx are not properly connected. I have tried switching them)
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Are you using any of the same pins used by the programmer?
     
  9. ssc953

    ssc953

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    Jul 17, 2016
    @(*steve*)
    I mentioned the connections I'm using in #1. Are you asking something else?
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Sorry, somewhere along the way I inserted a microcontroller in there somewhere.

    What speed is the uart set to and what does the module expect?
     
  11. ssc953

    ssc953

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    Jul 17, 2016
    USB to UART converter is set at 9600 8N1 according to device manager of PC.
    The radio modem has default configuration 9600 8N1
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Is the device you're trying to talk to an ESP-12 board (aka ESP8266)?
     
  13. ssc953

    ssc953

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    Jul 17, 2016
    The radio modem I am using is Dorji DRF1276DM.
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Well, at least it's not harmed by 5V :)

    Did you note this paragraph in the datasheet:

    Given that the pins are noted as having TTL inputs, it is entirely possible leaving an input open will cause it to float high. In any case, I don't see it's speced to have this pin left open.
     
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