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USB to Serial to MCU

timryder

I'm designing an application that will be using USB to serial to communicate to an ATMEGA328p  There will be a ton of communication and in some case some streaming of data.

I'm looking to design the best most robust USB --> Serial circuit I can to ensure that this works very well.  Can anyone offer me some help in this matter? 

 

I have something in place already but it doesn't seem to be working well.  I need more robust.  Also I was curious, whats the point of the resistors between the TX off the USB/Serial chip to the MCU?  Also the RX line as well.


Thanks!

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  • Most people get on well enough with the FTDI chips. If you have  a specific problem it might be possible to help if you can describe the setup and what goes wrong in detail.

     

    MK

  • in reply to michaelkellett

    I am using an FT232RL FTDI chip, but what i'm seeing is that every now and again the ATmega either fails to receive my string. I've been trying to see what could be the cause of it. Maybe it's noise on circuit board? I did implement 1k resistors from the FTDI to the MCU between the RX to TX and TX to RX lines. but to be perfectly honest, I'm a hobbyist and don't know the purpose of them.  I just mimicked another design from another engineer.  Maybe I need to increase this value?  Can anyone answer WHY I need these in there?

  • in reply to timryder

    i'll elaborate a little more, i'm using the "GRBL" firmware to run on the ATMEGA328p and communicating to it from a custom app that I wrote on the PC.  I know the PC is good because it seems to work fine with the Arduino Uno but not with my board.

  • in reply to timryder

    You probably don't need the resistors but 1k won't do any harm. Is this your own ATMega328 board - if so can you post a  schematic and  a pcb layout. How often does the system go wrong, do you just get some corrupted data or a complete system crash ? What communications protocol are you using and does it have any error detection/correction.

    I don't know enough yet to guess at  a cause yet but there are a few things we can do to pin it down.

     

    MK

  • in reply to michaelkellett

    I messaged you privately for now,

    I should note I'm a newbie and this is my first ever design. I'm teaching myself all the theory and design principles along the way.  SO any help and criticism from ANYONE is appreciated!

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  • in reply to timryder

    Hi Tim,

     

    You better check what is happening step by step.

    To check how is working your PC with the FT232, so,

         1.Disconnect the FT232 from the ATMega, and make a loopback (shortcircuit Tx Rx of the FT232) and check that everything you send from the app is immediatly received.

              a.If it fails check if flow control is enabled, if yes disable and try again.

              b. It works, step2

         2 Connect it to the ATMega, and try. Do you receive any data?   

              a. No. Check if you are using the rigth UART in the ATMega. Are you reading by pooling or by interruption?, if interruption check that the interruption is enabled.

              b. Yes, but wrong, Check that number of bits, parity and bit stop selected are the same in the PC and in the ATMega

              c. Yes and rigth. GREAT!!

     

    Hope that helps,

    Miguel

  • in reply to gihu

    if you,re using bare chip then make suer you have a 100nf/0.1uf capacitor on the reset line