Mailbag - 4x4 Matrix Keyboard for ESP8266 nEXT EVO Board

This Mailbag can also be seen as Part 4 of the ESP8266 nEXT EVO Analog Extension Board (AN1)


  In this part we will continue talking about the ESP8266 nEXT Evo 8 Bit I/O Expansion  Port based on the PCF8574 chip from NXP, testing procedures and software programming for the AN1 Board.

  After testing the Output of the 8Bit I/O Port it's now time to test also the Input function.
  So, what can be easier to use for such a processs than some pushbuttons for interaction?  I was thinking about some sort of buttons interface and because I just have arround a small 4x4 Matrix Keyboard why not directly a keyboard interface, especially that I'm waiting to receive some very thin membrane ones to be used for some projects.





Previous related Articles:

• New ESP8266 DevBoard - CBDB nEXT EVO - General presentation, schematics, PCB, etc 
• Part 2 - ESP8266 DevBoard - CBDB nEXT EVO - Firmware upload 
• SSD1306 OLED Display for ESP8266 nEXT EVO Board
• ESP8266 nEXT EVO - Analog Extension Board - Part 1 - General view, schematics, PCB, etc
• ESP8266 nEXT EVO - Analog extension Board - Part 2 - I2C Bus Protocol, scanbus example.etc
•  ESP8266 nEXT EVO - Analog extension Board - Part 3 - PCF8574 8Bit I/O Port Explained

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For any new CBDB orders/requests please feel free to use as usual:
     tech at esp8266-projects.com.

ESP8266 nEXT Evo bare PCB has also been made available directly at Dirty PCBs, our preferred PCB House for experimenting (**):
 http://dirtypcbs.com/view.php?share=9699&accesskey=91d782fd4a10943fd36ecc371c7ff2cd


(**) - Actually you have there 2 Boards for the price of one, a ESP8266 nEXT Evo together with a AN1 nEXT Analog Extension Board that brings you a 18Bit ADC (autoscale 0-40V input!), 4x12Bit DAC, Precison Temperature measurement, 8bit I/O port, etc.  
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What we will need:

• ESP8266 nEXT EVO Board
• ESP8266 nEXT EVO - Analog Extension Board - AN1
• 4x4 Matrix Keyboard (update: nice, very thin, membrane one here )
• For programming and uploading the driver and the software we will continue to use the LuaUploader as before.  

    Connection with the ESP8266 nEXT EVO Board is very easy, as Analog Extension Board - AN1 connector is fully compatible with the nEXT connector. Matrix Keyboard can be connected directly to the Analog Extension Board - AN1 8Bit I/O Port :

4x4 Matrix Keyboard connected to the ESP8266 nEXT Evo Board 8Bit I/O Expansion Port

 For more details and explanations please take a look at the Youtube Video from above: https://youtu.be/cVv7GCHmZ_o





Software implementation

For a better understanding of the way how the PCF8574 8Bit quasi-bidirectional I/O Port is working it might be a good idea to look at the prevoius related article and the PCF8574 Datasheet



1. Init I2C bus/interface

         -- init I2C nEXT BUS
       function i2c_init()
            i2c.setup(id, sda, scl, i2c.SLOW)
      end


2. Set PCF8574 PORT Register Function

function setPort( port, stat) 
    i2c.start(id)
    i2c.address(id, dev_addr ,i2c.TRANSMITTER)
    i2c.write(id,stat)
    i2c.stop(id)
end

3. Set Port function 

 Just a nicer way to write data to PCF8574 Register. Remember that we need to write a "ZERO" to the corresponding bit. We are sinking not sourcing !!

function setPortdata(p)
    pp = 255-p
    setPort(0x20,pp)
end

4. I/O Port READ Input

function read_input(dev_addr)
      i2c.start(id)
      i2c.address(id, dev_addr,i2c.RECEIVER)
      c = i2c.read(id,1)
      d = 255-string.byte(c)
      i2c.stop(id)
      --print("Read Value : "..d)
      return c,d
end

 5. OLED DISPLAY Related Functions

    5.1 Init OLED Display

 function init_OLED(sda,scl) --Set up the u8glib lib
     sla = 0x3C
     i2c.setup(0, sda, scl, i2c.SLOW)
     disp = u8g.ssd1306_128x64_i2c(sla)
     disp:setFont(u8g.font_6x10)
     disp:setFontRefHeightExtendedText()
     disp:setDefaultForegroundColor()
     disp:setFontPosTop()
     disp:setRot180()
end

 
     5.2 Print TEXT on Display

function PrintText()
  disp:drawStr(10, 25, str1)
  disp:drawStr(105, 25, str2)
end

 
     5.3 Print_LCD Function

function print_LCD()
   disp:firstPage()
   repeat
     PrintText()
     disp:drawFrame(2,2,126,62)
   until disp:nextPage() == false
end

6. Main Program

str1="Keyboard Input:"
str2="KEY"
id = 0
sda=2                           -- GPIO4
scl=1                            -- GPIO5
dev_addr = 0x20          -- PCF8574 Address
port={1,2,4,8}              -- COLS definition
row={128,64,32,16}     -- ROWS definition
key={'1','4','7','*','2','5','8','0','3','6','9','#','A','B','C','D'}   -- keys translation table

i=1
j=1
k=1

init_OLED(2,1)
print_LCD()

tmr.alarm( 0, 100, 1, function()
  setPortdata(port[i])                        -- activate COL[i]
  read_input(dev_addr)                     -- read active ROW

  while j<5 do
      if d==port[i]+row[j] then
            print("Col[i] = "..port[i])         -- for debug only
            print("Row[j] = "..row[j])        -- for debug only
            print("Read Value : "..d)           --for debug only
            print("Read Key   : "..k)            -- for debug only
            print("Pressed KEY Value : "..key[k].."\n")    -- print pressed KEY value
            str2=key[k]
            print_LCD()                              -- print also on Display
      end
      j=j+1
      k=k+1
      tmr.wdclr()
   end
  j=1

  i=i+1
  if i>4 then i=1
  end
  if k>16 then k=1
  end
end)