8 bits - PCF8574
I2C 8 bits - I2C - PCF8574
Fig. 1 I2C 8 bits
Description:
This board is an 8 bits port connected with an I2C interface. It is based around a PCF8574 chip.
It connects to a host with an I2C bus. It gives an extra 8 bits port, and can generate interrupt on pin change.
The board can be powered from 2.5 to 5V processor board.
Specifications:
Input voltage 2.5to 5V
InterfaceI2C
Port8 bits
Schematic:
The SDA and SCK I2C lines are pulled high by R5 and R6, while R7 and R8 protects the lines. R1 to R3 pull address line A0 to A2 low. The lines can be pulled high by SW1, and can be used to set the I2C slave address of the board.
C1 filters the power supply. R4 pulls the Int signal high, because the ouput of the PCF8574 is open drain.
The I2C connector JP6 and JP7 allow the board to be connected to an I2C bus in a chain. JP5 provides the interface to an 8 bits board. They are all optional. It depends how you want to connect to the board.
Fig. 2 I2C 8 bits schematic
Construction:
The PCB fits on a small single sided board. The PCF8574 is soldered on the bottom (copper) side. The other are on the top side.
Fig. 3 I2C 8 bits layout
Start with the lowest components, and continue with the higher ones. Don't forget IC1 on the coppwe side.
Pads 1 to 4 can be drilled to 3mm to fix the board, or put spacers.
| I2C Eeprom Component list |
|---|
| C1: 100 nF R1, R2, R3, R4: 100 K R5, R6: 22 K R7, R8: 220 IC1: PCF8574T (SO package) SW1: jumper 1x3 K1, K2: Connector AMP MT 5pins male (optional) K3: Connector AMP MT 10pins male (optional) |
How to use / Testing:
To check the board, you need a processor board running the I2C extension tutorial. Just make sure you set right I2C slave address with SW1.
Files and links:
Eagle PCB and schematics files for I2C 8 bits.PDFs of PCB, layout and schematics of I2C 8 bits.
PIC Tutorials for I2C extension.
NXP PCF8574 8 bits IO expander.