PCF8574: IC issues

I would guess that the resistance of the cable becomes too high. Can you measure it? What is your circuit?

Thanks for your response @ Clemens ladisch.  Actually, pcf8574 is configured as an input. I have connected eight switches with pcf8574. I've attached the circuit for your reference.

Hi Naveen,

What load is tied on the opposite side of the switch and cable? is it some kind of pull up resistor or is it tied directly to some Vcc/GND? The left side of the schematic shows a 10k pull up resistor, is that correct? 

Can you put a o-scope on the pins that are failing during the connection to a cable longer than 25 feet? 

-Bobby

1. switch tied with GND and one of the Pin from the PCF8574 Ic.

2. each pin of pcf9574 was pulled up with 10k.

3. Below 25 feet cable rising and falling happening properly.

4. above 25 feet cable,  from rising to falling happened only once or sometimes 2,3 times randomly. But after the switch is released, the pins did not return to rising position. (it should happen due to the 10k pullup resistor)

Can you show those waveforms?

no i have used a multimeter to check 3.3v or 0v 

And the voltage stays at 3.3 V or 0 V, and not some intermediate value? If yes, then this sounds like a defective wire or soldering issue.

Can you check, at the switch itself, that it correctly switches?

there's no problem with wire and soldering.

switch working properly.

after powerup, 1 or 2 times switches were working, I got data through scl,sda.

Then pcf8574 got stuck and slowly started to heat. Again I need to remove the power and plug it in again, then pcf8574 start working for a few moments, that may be 1 or 2 press of a switch. Then again same problem

At least some of the problems are caused by the pull-up resistors; they must not go above V_CC.

Can you place a scope probe the GPIO pins on the 8574 and try to capture a waveform of what the error is? 

-Bobby

i have used pullup resistor with 5v but VCC is 3.3v 

The pullups must go to 3.3 V.

but its works with pullup 5v and below 25feet wire length

But exceeding the recommended operating conditions and even the absolute maximum ratings removes any guarantee that the device will work, or even not be damaged.

Please show the waveform at the input pin.