PCF8574 vs PCF8591

[achechin]

Really simply question which still isn't clear to me.

What is the difference between PCF8574 and PCF8591? Please show it on examples rather than tell that one is digital IO other one is analog.

Thanks in advance!
Alex

[mattallen37]

You are right, one in digital IO, and the other is analog. Out of these two ICs, I have only used the PCF8574, so the following about the PCF8591 is only based on what I know of the IC, not from personal experimentation with it.

PCF8574:

• Write the lines low to sink current. << Drive LEDs etc. (BTW, it can sink, but not source current)
• Write the lines high (float the IOs, but with pullups) and then read the IOs. << Good for reading switches etc.

PCF8591:

• Read analog values (like from sensors). You could connect a POT, photoresistor/phototransistor, thermistor, etc.
• Write analog value. This is only one channel. I can't think of a good beginners example for this.

[floppi]

Hi,

Here are some examples :

https://sourceforge.net/apps/phpbb/mind ... f=2&t=1584

https://sourceforge.net/apps/phpbb/mind ... 574#p14800

and recently I used a PCF8574 to drive a ULN2803 with some transistor to drive 4 DC motors with bidirectional control up to 500ma, I will soon post this.