TinkerKit Tutorial: LCD: 06 – TWI

LCD Lessons:

  1. Windows Installation Guide
  2. Introduction to LCD
  3. LCD Serial
  4. LCD Local (No Arduino)
  5. Arduino & 2 Wires
  6. TWI

The TinkerKit! LCD also supports TWI connections. TWI stands for “Two-Wire Interface” and it’s another way to call the I2C bus technology. Basically it allows to connect multiple devices in series. This means that you can hook a large number of LCD screens, connecting them “in-line” using the two TWI ports, one for input and one for output. One of them must be the master (or you can use a TInkerKit! shield), while the others must run the TWI firmware. The TWI port has four pins, that’s why we need the 4-pin cable to connect them.

twi-zoom

First of all let’s connect two modules, then we move to the code. We need the TKLCD library that you can download from the library section of the website. If you downloaded it already, be sure to have the last version because TWI support has been added only recently.

Between the examples of the TKLCD library, there is one that is called TwiFirmware. We have to load it into one of or our LCD modules, the other module doesn’t need a firmware.

Now we have to declare our LCDs. One is a regular TKLCD_Local, while the TWI, it’s a TKLCD_Twi

TKLCD_Local local;
TKLCD_Twi twi;

Then in the setup we initialize them normally

local.begin();
twi.begin();

After this we can use them in the loop as a normal TKLCD, let’s try to write somthing on them:

local.print("Hi TWI");
delay(2000);
local.clear();
 
twi.println("Hi Local");
delay(2000);
twi.clear();

Ok, that was rather easy, but the cool thing about TWI is that you can connect as much modules as you want. Now we try to connect three LCD modules. One will be the local master and the other two are TWI slaves. We have to load them with the TWI firmware.

twi-zoom

If we have more than one TWI, in order to understand which one we are controlling we need to define a different address for each. Let’s open the TwiFirmware example in the TKLCD library and then, at line 88, there’s this command:

#define MATRIX_I2CADDR 0x33 // change this in order to communicate with another LCD

Every TWI module has an address that is defined in this line of the firmware program. By default it’s 0×33 but we can change it. If we have more than one module we have to define a different address for each module. Now we set one address to 0×33 and the other to 0×44, then we upload them.

Now all we have to do is program the master module. We don’t have to change barely anything from our program, we still have to declare just one TWI, but in the loop we have to set a different address everytime that we want to change the target TWI LCD. This is done using lcd.setActiveAddress(NEW_ADDRESS).

Here what we do is writing on the three screens in sequence:

local.print("I'm a local");
delay(2000);
local.clear();
 
twi.setActiveAddress(0x33);
twi.println("I'm TWI 0x33");
delay(2000);
twi.clear();
 
twi.setActiveAddress(0x44);
twi.println("I'm TWI 0x44");
delay(2000);
twi.clear();

By changing addresses, you can connect a large array of TWI devices.

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