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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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EI2C-9AG Manual v1.1
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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EI2C-9AG Manual v1.1
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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EI2C-9AG Manual v1.1
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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EI2C-9AG Manual v1.1
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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EI2C-9AG Manual v1.1
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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EI2C-9AG Manual v1.1
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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