Need clarification on I2C port Expansion from Arduino

[cvinothkumar]

I connected my Arduino UNO with the PCF-8575 16 BIT I2C IO Expander(NXP). Also given 5V supply to PCF-8575.

I Have Written the below program to enable the Pin-7 as OUTPUT and expecting 5V output at Pin-7. However, I am getting the Pin-7 voltage between 0.25 and 1.25V INSTEAD of 5V.

I have also attached the connection diagram. Also, we are using PCF-8575 library.

Am I missing anything?

#include "PCF8575.h"
#include "Arduino.h"

// Set i2c address
PCF8575 pcf8575(0x20);

void setup() {

  Serial.begin(9600);
  Serial.println("Started");
  pcf8575.pinMode(P7,OUTPUT);

  pcf8575.begin();
}

void loop() {
  pcf8575.digitalWrite(P7,HIGH);
  delay(100);
  pcf8575.digitalWrite(P7,LOW);
  delay(100);
}

[red_car]

You need a common GND between the Arduino and the pcf8575.

[cvinothkumar]

@red_car - We tried this approach. Still the same result. (Now pin-7 output measures 0V)

[red_car]

@cvinothkumar

We tried this approach.

Which PCF8575 library are you using?

@cvinothkumar

Now pin-7 output measures 0V

How are you measuring that? You are only setting it high for 100 ms at a time. Maybe you should change the delay (to say 5000) so you can actually measure it.

[cvinothkumar]

Please find the snapshot of the PCF 8575 library that we are using. Even after changing to 5000 delay I am getting the same results.

[red_car]

How are you measuring the voltage?

Did you try increasing the delay?

[red_car]

@cvinothkumar

We tried this approach.

Well you need a common ground... so keep trying it.

Also - does the PCF8575 have pull-up resistors?

[DrDiettrich]

@red_car

have pull-up resistors?

The data sheet is quite cryptic but external pullup resistors seem to be required.