title: Arduino: Packet loss on Serial communication
body: <p>I am trying connect multiple Arduino Mega Boards via their Serial pins to allow communication between the boards. I want to be able to connect an arbitrary amount of arduinos by daisy-chaning them and I want one board to be the master, taking control over the actions of the other boards. The master should be determined dynamically by the boards. I am aware that the daisy chaining method introduces delays to the communication due to the forwarding of packets, but so far I am planning on connection 4 boards at most. In the future this might increase to maybe 10 boards. My boards all have a separate power source, since they are connected to some other hardware which has its own power source.</p>
  
  <p>My idea was to connect the boards in such a way, that the master would be determined by the wireing of the boards. I thought about having the "Serial" port as 'To-Master' serial port and the "Serial1" port as "To-Child" serial port. The boards send hello messages on the "To-Master" serial port and the master replies if it received such a message on the "To-Child" serial port. If no answer is received after some seconds, the board determines itself to be the master.</p>
  
  <p>I wired the boards up by connecting the ground pins, and wiring RX1 of the master to TX0 of the child and TX1 of the master to RX0 of the child:</p>
  
  <p><img src="https://i.stack.imgur.com/a15XX.png" alt="Wiring of the boards"></p>
  
  <p>Basically my setup is working, since the boards do detect each other and exchange hello messages and replies. There is however a significant amount of packet loss or corruption which I would like to eliminate.</p>
  
  <p>As a simple measure of packet verification, I begin each packet with a "magic number". The receiving board looks for this byte and only tries to read a packet after receiving this byte. Any other bytes received are simply discarded.</p>
  
  <p>As it seems, it happens quite often that something is received on either serial port that does not start with the magic number and is therefore discarded. The timestamps of these events are however consistent with the timestamps of sending of the other board meaning that the packet was at least partially transmitted but somehow the magic byte got corrupted or discarded.</p>
  
  <p>Is this a known problem with the arduinos serial ports?</p>
  
  <p>Can it be related to my wiring?</p>
  
  <p>Are there any measures I can take to ensure a save delivery of the packets?</p>
  
  <p>Can it be a problem of the boards not reading the signal at the correct time (I used a baud rate of 9600)?</p>
  
  <p>I also looked into I2C communication, but I did not find any resource or information if it is possible to dynamically choose the master for this type of communication. Also in the documentation it stated, that it is important that all devices share a common power source which is not possible in my scenario. However, the basic master-slave principle of this I2C conforms with my requirements, as I have a master that sends commands to all other boards. Could I2C be utilized in my case?</p>
  
  <p>Thank you for your thoughts!</p>