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APC220 data drift

Posted by Jack Loo on December 17, 2012 at 9:27pm

Hi all,

I have just started to play with Arduimu v3.

I have modified the baudrate of the original arduimu code from 38400 to 9600 and using apc220 as my wireless module.

and what I get was as below, data drift for every few line.

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May I know if this is normal?
what can i do to handle this in my ground station, please advice, thank you very much!

P/S: I didn't connect GPS.

Jack

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Replies

  • Nick Goodey December 23, 2012 at 12:12am

    Jack,

    I will be interested in how the APC220 performs as its a low cost alternative to an Xbee please keep me posted 

    Nick

  • Nick Goodey December 23, 2012 at 12:11am

    Hello Jack,

    In some circumstances this is normal if you are looking at the raw data in the receiver end of the system. The data could be getting corrupted. I have an Xbee setup and still see these sort of problems when testing. I mitigated the problem as by adding a checksum into my data packet. 

    Could be you are overrunning the buffer if you look at the long line its a whole packet then it has no CR LF and another packet is appended but the beginning is missing. If you added a checksum you would be able to reject these bad packets as in the real world you will always get occasional drop outs and bad data

    I have a checksum on my outgoing packet as follows

    //input values

    TxVal[0] = map(TxVal[0], 0, 329, 0, 1790); // scale it to use it with the servo (value between 0 and 180)
    TxVal[1] = map(TxVal[1], 0, 1023, 0, 1790); // scale it to use it with the servo (value between 0 and 180)
    TxVal[2] = map(TxVal[2], -142, 171, 0, 1790); // scale it to use it with the servo (value between 0 and 180)
    TxVal[3] = map(TxVal[3], -170, 193, 0, 1790); // scale it to use it with the servo (value between 0 and 180)
    TxVal[4] = map(TxVal[4], -505, 515, 0, 1790); // scale it to use it with the servo (value between 0 and 180)
    TxVal[5] = map(TxVal[5], 545, -477, 0, 1790); // scale it to use it with the servo (value between 0 and 180)

    //RSSI
    rssi = pulseIn(10, LOW, 200);

    TxVal[7] = rssi;

    TxVal[8] = 0;
    TxVal[8] |= (digitalRead(5) << 0);//joy 2 push
    TxVal[8] |= (digitalRead(6) << 1);//pb
    TxVal[8] |= (digitalRead(7) << 2);//slide
    TxVal[8] |= (digitalRead(8) << 3);//toggle

    TxVal[9] = (micros() - time);




    //calc checksum
    int chk = 0;
    for(int i = 0;i < 11;i++)
    chk += TxVal[i];

    sprintf(buf, "C,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,%d,\n", TxVal[0], TxVal[1], TxVal[2], TxVal[3], TxVal[4], TxVal[5], TxVal[6], TxVal[7], TxVal[8], TxVal[9], chk);

    Serial.write(buf);

    My receiver code


    int ExtractPacket()
    {

    int Lchk = 0;
    int channel = 0; //initialise the channel count



    p = &inputString[0];

    while ((str = strtok_r(p, ",", &p)) != NULL) // delimiter is the comma
    {

    TxTemp[channel] = str.toInt(); //use the channel as an index to add each value to the array

    Lchk += TxTemp[channel];

    channel++; //increment the channel

    if(channel > MAX_CHAN)
    break;
    }

    p = NULL;
    inputString = "";

    //Process in comming data
    if(channel > 2)
    {
    //Remove the remote chk from the total
    Lchk -= TxTemp[channel-2];

    //Checksum
    if((Lchk - TxTemp[channel-2]) == 0)
    return channel;

    }

    return -1;
    }


    Here is my code, its very simple code

    TX https://docs.google.com/open?id=0B8mGA5b7qZ15dFJHaEdxbmF5dTQ

    RX https://docs.google.com/open?id=0B8mGA5b7qZ15b1pDOHA1SnU3cEE

    Hope this helps

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