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SN74HCT04: RE: Oscilloscopes and Using Selected Chips to Read Data/Frequency

silver2row
Intellectual 540 points

Part Number: SN74HCT04

Hello There and While I Research Ideas,

 

I am trying to figure out how to read my oscilloscope correctly with a 3.3v CMOS logic source, i.e. GPIO and/or PWM peripherals from an am335x SoC.

I thought the SN74HCT04 would be a winner in this category but I am not aware of it being correct just yet. Does the SN74HCT04 work with 5v oscilloscopes while reading frequencies of 3.3v in time?

I read online, finally and I think the data is correct, that the 74HCT family of chips produces the correct logic for the task. So and to repeat here:

  1. The oscilloscope reads at 5v and 2v but not at 3.3v. <-- incorrect
  2. I was thinking of purchasing some inverters to handle this task of translation from 3.3v (am335x GPIO/PWM) to 5v (oscilloscope). <-- is this needed?
  3. If this makes sense, please send some feedback (any and all are okay by me).

 

Seth

P.S. Thank you again for your time. I tried to handle getting online at the e2e forums but was sent to this page online to handle my query. 

  • 0
    TI__Guru* 97666 points

    Hi Seth,

    silver2row said:
    P.S. Thank you again for your time. I tried to handle getting online at the e2e forums but was sent to this page online to handle my query. 

    You have successfully posted your question to the E2E forums - in particular, the Logic Forum.

    silver2row said:
    I am trying to figure out how to read my oscilloscope correctly with a 3.3v CMOS logic source, i.e. GPIO and/or PWM peripherals from an am335x SoC.
    silver2row said:
    The oscilloscope reads at 5v and 2.2v but not at 3.3v.

    I've never seen an oscilloscope that did not show voltage waveforms over time. Can you point me to exactly what instrument you are using? I suspect you mean 'logic analyzer' and it does not support 3.3V input signals. If I know what you are using, I may be able to help further.

    If this is the case, I expect that the 3.3V signals you have will be sufficient to trigger the input of the logic analyzer -- have you tried this already and the signal does not appear at all?

    If your logic analyzer has a 2.2V trigger level, I expect it would show your 3.3V signal also.

    silver2row said:
    I was thinking of purchasing some inverters to handle this task of translation from 3.3v (am335x GPIO/PWM) to 5v (oscilloscope).

    If this is just a one-off usage and you're doing it with a breadboard, you can use almost any logic gate to convert from 3.3V to 5V. The HCT04 will do this in one step, but if you have another gate on hand (perhaps an HC04 or LS04), that would likely also work for your application.

    I wouldn't recommend this method for mass production - but it sounds like you just need to get a few signals converted for your project.

  • 0 in reply to Emrys Maier
    Intellectual 540 points

    I am new to handling oscilloscopes and performing reviews of waveforms. 

    The oscilloscope works. It can read my GPIO pins at 3.86v (this is what the oscope states). I was getting poor readings because of my vertical/horizontal positioning. 

    The brand is Rigol. The type is a DS1102E. It has been discontinued by the mfg. recently. So, no more upgrades to the firmware are available. Blah.

    Seth

    P.S. I appreciate you taking time out to reply. If you have any more questions for me or ideas to handle this specific oscope, please reply once more. Thank you again. 

  • +1 in reply to silver2row
    TI__Guru* 97666 points

    I have a similar scope at home - in fact, I made a video showing how to use it not too long ago here: www.youtube.com/watch

  • 0 in reply to Emrys Maier
    Intellectual 540 points

    Thank you. I will watch it.

  • 0 in reply to Emrys Maier
    Intellectual 540 points

    I watched the video. Very informative and educational for me...thank you.

    On mine, the oscilloscope, there are two channels and an Ext Trig channel that accepts a probe. 

    So, for instance, I am reading a GPIO pin from the am335x on my DS1102E oscilloscope. I can see the visual waveform now. I am not exactly sure of everything just yet. It seems a bit unlike a photo or photos I have seen of GPIO waveforms online.

    Seth

    P.S. In any light here, thank you. I will keep trying and reading up on ideas.