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Thread: 3.3v to 5v level shifter

  1. #1

    Post 3.3v to 5v level shifter

    hi,

    i have tried to buy max3372, lm3350 and QS3861 Ic's in Mumbai.

    i have to interface aubtm-20(3.3v supply) with 8051(5v supply)

    does anyone here know where i can buy these IC's or are there any alternatives to this.

    level shifting is needed for UART communication betweeen autbm-20 and 8051.

    thank you,

    Vivek

  2. #2
    Senior Member Cyborg
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    Sep 2004
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    Option (A)
    direct link without silicon. but protective resistor (5.1kohm~10k) between Tx_8051 and Rx_3.3ic.
    similarly add resistor to any another output of 8051(5V0 to 3.3Vic input.
    this method relies and works on -
    -output levels of 8051, 5v are ok can be read by 3.3v logic inputs as long as you are not injecting damaging current in the lowevr voltage input
    -input levels "maybe" ok, hopefully the threshold of 8051 logic input is about 2.5V.

    Option(B)
    for 8051 output, same as option-A, but to eliminate the "maybe" on inputs -
    add a BJT with base connected to 3.3voutput through 1kohm. the collector goes to vcc5V, through 1kohm. the collector connects to 8051input.
    the BJT could be your favourite bc547 etc.
    Vivek
    --
    " To get working ideas effectively, I try to fail as fast as I can. "
    Richard Feynman
    --
    http://www.youtube.com/watch?v=JqlawTD_9B0

  3. #3
    Senior Member Cyborg
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    Question - if know what logic operation will be performed by using a BJT in option-B, you can go ahead and try the two solutions, if not, you are better off searching for a logic translator IC.
    Vivek
    --
    " To get working ideas effectively, I try to fail as fast as I can. "
    Richard Feynman
    --
    http://www.youtube.com/watch?v=JqlawTD_9B0

  4. #4
    Senior Member T-1000
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    Best use
    74HC4050

    I have used it with My MicroSD Module
    http://extremeelectronics.co.in/news/microsd-module/
    Avinash Gupta
    ************
    www.eXtremeElectronics.co.in

  5. #5

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    @vivek

    one more question:

    do you think the circuits you mentioned can operate at 115200bps baud rate?

  6. #6

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    @avinash

    74HC4050 is a high to low level shifter.
    what about low to high level shifting?

  7. #7
    Senior Member Cyborg
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    >do you think the circuits you mentioned can operate at 115200bps baud rate?

    Well, first i answered this , then I realized I would steal the joy of designing and learning from you if I gave you an instant answer.
    Rather Id show you how its done -

    First - 115.2kbps is how many KHz in worst case ? (quiz). say it is "B"
    Second- look up the datasheet of BC547, what is the gain bandwidth product of that transistor ? say "F"
    Although you will run at gain of 1, in that case as long as F > B you are good.
    Even if you run at gain of 10, then need to verify that F/10 > B.
    As a thumb rule, simply verify is F/100 > B

    besides that though -
    I still see that it will require a little more thought and consideration than just trying the circuit directly -
    -i.e. -- The UART works on reverse logic,
    since you don't have a max 232, (which is basically inverters, with RS232 level shifters) - if you directly connect to 8051 following my suggestion, you might have to invert the signals to logic understood by 8051 uart pins.
    Which simply implies, using more BJTs. (a bjt inverter)
    So for 3.3v ---> 5V you already get and inverter built-in if you follow option-B.
    for 5v --> 3.3v-, you can figure that out.

    Best Regards
    Vivek
    Last edited by Vivek; 03-12-2011 at 03:32 AM.
    Vivek
    --
    " To get working ideas effectively, I try to fail as fast as I can. "
    Richard Feynman
    --
    http://www.youtube.com/watch?v=JqlawTD_9B0

  8. #8

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    i know it was a silly question from me. It's just that, i am under some much pressure and hardly any time-left to complete the whole project that I selfishly tried to reduce my calculation work and ask you directly instead.
    anyways, I deeply thank you for helping me out. I will surely try out the methods mentions by you and reply if it works out.

    Regards,
    Vivek M

  9. #9
    Senior Member Cyborg
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    it was not silly question. it was far better than , asking a code or circuit outright.
    good luck
    Vivek
    --
    " To get working ideas effectively, I try to fail as fast as I can. "
    Richard Feynman
    --
    http://www.youtube.com/watch?v=JqlawTD_9B0

  10. #10

    Default

    its not the fault of students who ask for direct codes or circuit layouts. Its the education system that sucks. Only theory is taught is colleges. but doing electronics in pratical and in theory is Completely different. Understanding a concept in electronics if far easier than implementing it in practical. All because we ignore simple basics in electronics. Hope one day the system focuses more on practicals.

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