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EI2C-9AGI2C bus 8 Inputs Opto-Isolator

Main Features

PCF8574A I2C I/O expander

100KHz I2C bus frequency

Address by 3 jumpers for use of up to 8 devices

Interrupt output

5V power supply with inverse polarity protection

Compatible with most microcontrollers

~6 to ~15 VDC continuous input voltage

Inverse polarity protection of each opto-isolator

channels

Small board 28 x 81.5 mm

INTRODUCTION

The EI2C-9AG is a board for remote 8-input expander for I2C bus based on PCF8574A.

Making it ideal as an isolation input expander for I2C bus. It is designed to compatible with most

5V microcontrollers.

BOARD DIAGRAM

Figure 1. Board diagram

Inverse

Polarity

Protection

I2C

Expander I/O

Controller

(PCF8574A)

8 channels

Opto-Isolator

Inverse

Polarity

Protection

8 8

VCC

GND

SCL

SDA

INT

A0 A1 A2


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EI2C-9AG Manual v1.1

BUS SIGNALS

5-pin IDC(2.54mm) connector consists of 5V, GND, SCL, SDA and INT signals. The 5V

and GND are power supply which must be supplied from external. The board has an inverse

polarity protection circuit to prevent damage from inverse polarity of 5V and GND. The SCL and

SDA are I2C bus signals which must be connected to SCL and SDA pins of microcontroller. For thelast signal is INT which can be connected to the interrupt logic of microcontroller.

Figure 2. I2C bus and power supply pins

INTERFACE TO MICROCONTROLLER

5V and GND must be supplied from external and also on board has an LED to show power

supply. The SCL and SDA pins must be connected to SCL and SDA pins of microcontroller

respectively. Remember 10K resistors must be connected to pull-up the SCL and SDA signals of

I2C bus. The INT signal may be connected to the interrupt pin of microcontroller to inform the

microcontroller if there is incoming data on its inputs.

Figure 3. Interface to microcontroller

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A0

A1

A2

5V

GND

SCL

SDA

INT

Microcontroller

5V

10K x 2

VCC

GND

SCL

SDA

INT0

A0

A1

A2

5V

GND

SCL

SDA

INT
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BUS ADDRESS

The board use PCF8574A as remote input expander for I2C bus. Which the PCF8574A has

address as figure below. Bits D3,D2,D1 are changed by jumpers

Figure 4. Bus address

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A0

A1

A2

A0

A1

A2

A0

A1

A2

A0

A1

A2

A0

A1

A2

A0

A1

A2

A0

A1

A2

A0

A1

A2

A0

A1

A2

1 A111 1110S

0x7F

1 A011 1110S

0x7D

1 A101 1110S

0x7B

1 A001 1110S

0x79

1 A111 0110S

0x77

1 A011 0110S

0x75

1 A101 0110S

0x73

1 A001 0110S

0x71

Open (High)

Close (Low)

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W


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INPUT DIAGRAM

The board use photocouplers to isolate input signals from the PCF8574A. Each inputs can

support up to15Vdc when input voltage is continuous voltage. However they can support up to

30Vdc when pulse voltage is supplied. All inputs have the inverse polarity protection circuits to

prevent damage of photocoupler from inverse polarity of input voltage.

Figure 5. Input diagram

When read input logic via the PCF8574A. The input logic will placed on data frame of the

PCF8574A as figure.

Figure 6. Input logic to data frame

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P0P1P2P3P4P5P6P7

IN 0IN 1IN 2IN 3IN 4IN 5IN 6IN 7

- +- +- +- +- +- +- +- +

IN 0IN 1IN 2IN 3IN 4IN 5IN 6IN 7

- +- +- +- +- +- +- +- +

P0P1P2P3P4P5P6P7A1A0A1A21110S A ... ... ... P

ADDRESS BYTE DATA BYTE1 DATA BYTE n

PFC8574A data frame


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APPLICATIN NOTE 1

Connect constant voltage to input of board directly.

Figure 7. Constant voltage

APPLICATION NOTE 2

Use switches to on/off input voltage.

Figure 8. Switch on/off positive voltage

Figure 9. Switch on/off negative/ground voltage

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A0

A1

A2

A0

A1

A2

A0

A1

A2


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APPLICATION NOTE 3

Use transistors to on/off input voltage.

Figure 10. NPN transistors by open collector

Figure 11. NPN transistors by open emitter

Figure 12. PNP transistors by open collector

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A0

A1

A2

A0

A1

A2

A0

A1

A2


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Figure 13. PNP transistors by open emitter

APPLICATION NOTE 4Use several input types to turn-on/turn-off input voltage

Figure 14. on/off input voltage

Figure 15. on/off input voltage

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A0

A1

A2

A0

A1

A2

A0

A1

A2


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SPECIFICATION

Bus speed 100Khz

Maximum board on a bus 8 boards

Maximum input voltage ~6 to ~15Vdc (continuous voltage), ~15 to ~30Vdc (pulse voltage)

Input isolation voltage 3.7kVDC

Input channels 8

Input current 6Vdc ~4mA

12Vdc ~10.8mA

15Vdc ~13.8mA

24Vdc ~22.2mA

30Vdc ~28.2mA

Power supply voltage 5Vdc

BOARD DIMENSION

Figure 16. Board dimension

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A0

A1

A2

L

W

a

b

c

c

L

W

a

b

c

1.100

0.250

0.125

0.025

3.207 81.45

27.94

6.35

3.18

0.63

unit mminch

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