ESP Basic -3 - PCF8574 I2C I/O 8 x independent switches example

8 x Independent switches driver Example :






  
   After doing last time the Mutually exclusive 8x Switch driver example, now is time for a 8 x independent switches implementation .


What we will need: 

• ESP8266 nEXT EVO Board 
• ESP8266 nEXT EVO - Analog Extension Board - AN1 (PCF8574 onboard) 
• 8 LED Port Tester as described in the related Article 
• For programming and uploading the driver and the software we will use ESP8266 Basic . 

      This is how is looking the setup on a breadboard, for a better visibility:

Software implementation:

Something to remember: 

• PCF8574 can SINK but NOT SOURCE much current - 100uA only (it cannot output high, if you want). Look at the above example how is connected the LED for SINKING current.
• Each of the 8 GPIOs have a minimum guaranteed sinking current of 10 mA per bit at 5 V.
• Each pin needs its own limiting resistor to prevent damage to the device!! keep under 25mA/pin.
• Maximum device limit sink current in about 80mA. If you need more, look after PCA8574 (200mA max sink current!)

For more details please take a look at the PCF8574 Datasheet


ESP8266 Basic code: 

let address = 32 'PCF8574 I2C Address

i2c.begin(address)
ss = 0 xor 255 'XOR - Bit masking for the desired I/O pins
i2c.write(ss)
i2c.end()
button "1", [1]
button "2", [2]
button "3", [3]
button "4", [4]
button "5", [5]
button "6", [6]
button "7", [7]
button "8", [8]
button "OFF", [9]
wait

[9]
i2c.begin(address)
ss = 0 xor 255 'XOR - Bit masking for the desired I/O pins
i2c.write(ss)
i2c.end()
wait

[1]
i2c.begin(address)
ss = ss xor 1   'XOR - Bit masking for the desired I/O pins
i2c.write(ss)
i2c.end()
wait

[2]
i2c.begin(address)
ss = ss xor 2
i2c.write(ss)
i2c.end()
wait

[3]
i2c.begin(address)
ss = ss xor 4
i2c.write(ss)
i2c.end()
wait

[4]
i2c.begin(address)
ss = ss xor 8
i2c.write(ss)
i2c.end()
wait

[5]
i2c.begin(address)
ss = ss xor 16
i2c.write(ss)
i2c.end()
wait

[6]
i2c.begin(address)
ss = ss xor 32
i2c.write(ss)
i2c.end()
wait

[7]
i2c.begin(address)
ss = ss xor 64
i2c.write(ss)
i2c.end()
wait

[8]
i2c.begin(address)
ss = ss xor 128
i2c.write(ss)
i2c.end()
wait

This is how is looking the interface in the Web Browser after running the above program:

PS: credit for the XOR Bit masking goes this time to Forlotto from the esp8266.com forum who posted quicker than me this elegant solution :)