Week 13: Networking and communication
Group assignment: Send a message between two projects
Individual assignment: Design and build a wired and/or wireless network connecting at least two processors
Individual assignment: Design and build a wired and/or wireless network connecting at least two processors
for this week I had to use two boards that I made and connect them with a network
(one is the board I made in the week 10 and the other is the one I made during week 6 ).
There are a lot of types of Networks, but i chose the I2C protocol.
I2C
The I2C Protocol is a protocol intended to allow multiple slave digital integrated circuits (chips)
to communicate with one or more master chips.
Like the Serial Peripheral Interface (SPI), it is only intended for short distance communications within a single device.
Like Asynchronous Serial Interfaces it only requires two signal wires to exchange information.
How does I2C work?
I2c it's a 2 wire protocol for a 7-bit addressing bus and it's using the SDA line for data transfer and SLC the clock line.
The clock signal is always generated by the current bus master. Some slave devices may force the clock low at times to delay the master sending more data
(or to require more time to prepare data before the master attempts to clock it out).
I took the most important part from this tutorial that explain how Master and Slave will communicate.
"To initiate the address frame, the master device leaves SCL high and pulls SDA low. This puts all slave devices on notice that a transmission is about to start.
The address frame is always first in any new communication sequence. For a 7-bit address, the address is clocked out most significant bit (MSB) first, followed by a R/W bit indicating whether this is a read (1) or write (0) operation.
The 9th bit of the frame is the NACK/ACK (Not Acknowledge/Acknowledge) bit. This is the case for all frames (data or address). Once the first 8 bits of the frame are sent, the receiving device is given control over SDA. If the receiving device does not pull the SDA line low before the 9th clock pulse, it can be inferred that the receiving device either did not receive the data or did not know how to parse the message. In that case, the exchange halts, and it’s up to the master of the system to decide how to proceed.
After the address frame has been sent, data can begin being transmitted. The master will simply continue generating clock pulses at a regular interval, and the data will be placed on SDA by either the master or the slave, d epending on whether the R/W bit indicated a read or write operation.
Once all the data frames have been sent, the master will generate a stop condition by a 0->1 (low to high) transition on SDA after a 0->1 transition on SCL, with SCL remaining high. During normal data writing operation, the value on SDA should not change when SCL is high, to avoid false stop conditions.""
for my project I will program my boards so that the master sends to the slave a value and this value is read by the slave, that will emitt a blink. Onestly for this project Simone Guercio helped me a lot.
Since the boards have AtTiny processor, this influenced the sketch's realization so I downloaded and installed the library from github, this for the master and this fore the slave. After this I made the sketches:
Master
I took the most important part from this tutorial that explain how Master and Slave will communicate.
"To initiate the address frame, the master device leaves SCL high and pulls SDA low. This puts all slave devices on notice that a transmission is about to start.
The address frame is always first in any new communication sequence. For a 7-bit address, the address is clocked out most significant bit (MSB) first, followed by a R/W bit indicating whether this is a read (1) or write (0) operation.
The 9th bit of the frame is the NACK/ACK (Not Acknowledge/Acknowledge) bit. This is the case for all frames (data or address). Once the first 8 bits of the frame are sent, the receiving device is given control over SDA. If the receiving device does not pull the SDA line low before the 9th clock pulse, it can be inferred that the receiving device either did not receive the data or did not know how to parse the message. In that case, the exchange halts, and it’s up to the master of the system to decide how to proceed.
After the address frame has been sent, data can begin being transmitted. The master will simply continue generating clock pulses at a regular interval, and the data will be placed on SDA by either the master or the slave, d epending on whether the R/W bit indicated a read or write operation.
Once all the data frames have been sent, the master will generate a stop condition by a 0->1 (low to high) transition on SDA after a 0->1 transition on SCL, with SCL remaining high. During normal data writing operation, the value on SDA should not change when SCL is high, to avoid false stop conditions.""
for my project I will program my boards so that the master sends to the slave a value and this value is read by the slave, that will emitt a blink. Onestly for this project Simone Guercio helped me a lot.
Master and slave
Since the boards have AtTiny processor, this influenced the sketch's realization so I downloaded and installed the library from github, this for the master and this fore the slave. After this I made the sketches:
Master
Basically the master with TinyWireM.beginTransmission connects with the slave with the same number.
TinyWireM.send sends a value to the slave.
Slave
With TinyWireS.onReceive the slave knows that when it receives the value number 1 the led will be on, otherwise it will be off.
After I uploaded the sketches I connected the master to the FTDI (only ground and vcc) cable and the slave to the SPI through 4 cables. Unfortunately it didn't work,
probably it was the TinyWireS library.
Update 24/05
Since I had some problems during this week,
I tried networking again, this time using serial communication.
The difference between I2C and serial communication is the way the data travels: in Serial
the data travels one at a time.
Communication travels thanks to the clock that marks the timing.
I used the hello board of week 6 and the satshakit created for the final project.
Looking at some documentations (in particular this)
I saw that I could use the softwareserial library for both codes. Below the codes and the explanation of how they work.
MASTER
SLAVE
At the beginning the communication didn't work. After several attempts to check the connections and codes,
we (me and Simone)
made a blink to test the slave board and we noticed that the time was different from what it should have been.
Double-checking the settings of the board on arduino ide we noticed the error: the fuses had been set with an external 8Mhz crystal and not at 20Mhz,
consequently the two boards were not "speaking" each others. So after changing the setting, rewrote the bootloader and reload the code finally everything worked.
MASTER
 |
I have defined the rx and tx pins and the led pin (because it will be the powerled). Initially I wanted to use the button too but being the reset I should have created a no-return command (ie the board would no longer be reprogrammable) and so I let it go. In setup I defined the rx as INPUT and tx as OUTPUT since it is through these two pins that the serial communication takes place: tx sends the data and rx receives them. The command is described in void loop: the master will send the signal 1 and after a second the signal and after a second it starts again. |
SLAVE
 |
After re-define rx and tx I define the led that will blink and set an int as rxbuffer in void loop and I declared that like serial.read. If the slave receives 1 the led will be off, else it will be on. |
Group assignment
For this week we have to get our boards to communicate so we decided to do two types of communication: the first in serial and the second in I2C.Below the codes for the serial communication.
This is the slave-code that I made for my board for the final project.
Marco setted his board as master and this is his code.
After connecting all the wires we linked the vcc and the gnd to the ftdi cable and connected it to the pc for the voltage. And this is the result
Then we made an I2C networking, this time we used 2 node (Marcos'Hello board and my hello board too) and the previous board that we setted as slave now is the master (it made a career). Also we used a mini board (made by Simone, here the link to his page) to split the pin in order to connect both the boards.
Below the codes.
Master
First slave (my hello board)
Second slave (Marco's hello board)
FINAL RESULT
After linked all the cables with the right pins the network was ready, so we attached it to the pc with FTDI cable.