Olinuxino A13 and PCF8574 - I2C IO Expander

Started by Stephane80, January 22, 2013, 10:31:51 pm

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Stephane80

January 22, 2013, 10:31:51 pm Last Edit: January 25, 2013, 11:56:44 pm by Aqua-Passion
Hello , I have a PCF8574  I2C IO Expander like this:
http://cgi.ebay.fr/ws/eBayISAPI.dll?ViewItem&item=280844356391
from my arduino
can I use it with the Olinuxino A13
if so, on what pins?
Can I drive 5v items with it ?

thanks

Stephane80

nobody has an idea?
I can safely test?
Or there is a risk by plugging the module supplied with 5v?
thanks

JohnS

It should be obvious to check manuals and circuit diagrams for both items as you could easily damage one or both items if you fail to do that.

If that is too hard then you should find/hire someone competent to do it for you.

Stephane80

Thank you for your answer
I think I'll try anyway
I have not found anyone to test
I think anyway voltage transitan on sda / scl must be standardized (i2c)
+5 vdc should be for input / output

jeroends

First read the data sheet of the chip.
The chip can be powered with 3.3v but than your outputs will also be at 3.3v. If this is not a problem for you, nothing can go wrong.
If you want to power the chip at 5v you'll have to use a level convertor to convert to 3.3v i2c bus to 5v and backwards. (ex https://www.sparkfun.com/products/8745)
If you don't use this, your a13 chip will get 5v at it feets and will crash!!

JohnS

Permanent damage or complete destruction of the A13 is a risk.

Do not use 5V unless you KNOW it will be OK.

Stephane80

Ok thank you
I think I had not properly understood the datasheet
I have read
QuoteDC CHARACTERISTICS
Supply
VDD supply voltage min 2.5 max 6.0 V

Input SCL; input/output SDA
VIL LOW level input voltage min -0.5V  max +0.3VDD
VIH HIGH level input voltage min 0.7VDD max VDD + 0.5V

reading quickly I understood
-0.5v / +0.3 V for sda scl :-(

I'm looking to buy a level convertor

I have to control a 5v arduino relay board  so I need 5v
thanks for your help !

JohnS

Look on the net, there are simple ways to do that using a transistor or some of the boards allow 3V for the input (and 5V for the relay).

John

Stephane80