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Permalink Reply by Nick Goodey on December 23, 2012 at 1:11am

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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Permalink Reply by Jack Loo on December 23, 2012 at 1:59am

Ok, thank you so much for the idea and codes!

Jack

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Permalink Reply by Nick Goodey on December 23, 2012 at 1:12am

Jack,

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

Nick

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Permalink Reply by Jack Loo on December 23, 2012 at 2:01am

Nick,

hmm... I am not sure how to tell you its performance as I am still new to wireless module.
maybe you can ask me some questions and i will check for you?

Jack

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Permalink Reply by Nick Goodey on December 23, 2012 at 1:17pm

Just interested in your over all impression of the APC220.

One thing I need for the remote control is low consistent latency, even without instruments this is easy to see when you are driving a servo from a joystick over the air.

Have a look at this video you can see and here what I mean as a bad...

You can see how much smoother this example is 

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Permalink Reply by Jack Loo on December 28, 2012 at 1:03am

sorry for the late reply..
yup, this module is work fine for me and works very well after i throw away the corrupted data using your guideline, thanks!

Jack

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