Must reset Arduino Uno to get PCF8574 work correctly.

Projects Networking, Protocols, and Devices
1

Hi,

in my projekt I use two PCF8574 chips.
The first one to control 2x16 LCD display (LCDI2C4Bit library) The second one together with ULN2803 as port expander, all 8 ports as output (PCF8574 library: [Librairie Arduino] PCF8574 – PCF8575 | Skyduino - Le DIY à la française).
When I use Arduino Uno rev.2 SOMETIMES I have to reset the Arduinio after turning it on (with the reset button) to get the PCF8574 chips work correctly (when I do not reset, all ports are HIGH all the time and the LCD does not work).
When I use my old Arduino Diecimila (with Atmega328) it works great every time I turn it on.

Do you have any idea, is it some power-problem?

Thanks for help!

2

How clean is your power supply and how are you turning it on?

3

MarkT:
How clean is your power supply and how are you turning it on?

What do you mean with 'how clean'? I've soldered all parts to a universal plate like this one http://www.majstar.com.pl/images/plytki%20ok/dip3.jpg?PHPSESSID=76b250fdc6b40976f5fedc59bcf2f0c7. The parts/pins are connected with wires.
This is not my project, but it shows how I do it:
http://www.instructables.com/files/deriv/F2Q/270S/G9M4OS1A/F2Q270SG9M4OS1A.MEDIUM.jpg

To turn the Arduino on I put the (12V-1250mA Power-Supply plug) or (USB Cable) into the Arduino socket.