PCF8574 IO Expansion Board

Hi,

I've bought this item from ebay - PCF8574 IO Expansion Board:

My intent is to connect several digital pots to the arduino board.

As far as I understand, the digital potentiometers must support the I2C protocol?

The expander is I2C bus.I have no idea if just the expander gets I2C instructions and could have SPI devices connected through it.

Actually this is my first project. The need is to control 5 digital pots via IR remote control + 5 relay switches

Regards.

emosms:
Hi,

I've bought this item from ebay - PCF8574 IO Expansion Board:

My intent is to connect several digital pots to the arduino board.

As far as I understand, the digital potentiometers must support the I2C protocol?

The expander is I2C bus.I have no idea if just the expander gets I2C instructions and could have SPI devices connected through it.

Actually this is my first project. The need is to control 5 digital pots via IR remote control + 5 relay switches

Regards.

This device is an I2C slave. It has 8 input/output pins, It has weak (100uA) (high) drive and 25mA (low) drive. You send it an 8bit value that is expressed on its output pins, you can read the true status of the pins. If you have previously written a Low to any of the pins the read will return low for that pin. If the previous write set the pin to high, the attached device could pull that pin low. But if the attached device tries to drive a pin HIGH (5V) that was commanded (written) LOW (0V) one of them is going to explode. the PCF8574 can sink 25mA per pin.

Hopefully your digital pots can have individual I2c address. that way they can all be on the I2C bus. This PCF8574 could control the relays directly as along as the coil currents are below 20mA and only 4 are turned on at a time. If either of these statements are not true, you will have to provide some driver circuits for the relay's.

Chuck.

So have to find out :):

For the relays, I also purchased some brick modules to experiment.
There are smal IC-s, not sure if drivers or logical gates:


(this one has big ones, hopefully drivers)



(these have logical gates only?)

At least they should have pull-up resistors.

For two of the relays I planned to make latching triggers, so that the relay is switched on/of by a signal applied once. Both by the microcontroller and manually with a button.

It would be easier in terms of… soldering, to put a current driver only and control the latching through the microcontroller.

Thx, for reminding me, the first one has opto couplers probably, and could be powered externally.

The other two don't have. The relay coil resistance is 70 ohms, so can't be powered through the expansion board.

Have to check if can be powered from arduino uno and nano (the boards i got)

emosms:
Thx, for reminding me, the first one has opto couplers probably, and could be powered externally.

The other two don't have. The relay coil resistance is 70 ohms, so can't be powered through the expansion board.

Have to check if can be powered from arduino uno and nano (the boards i got)

You will need to know the coil voltage in addition to the resistance. The Arduino power supply (VCC) is limited to about 100ma of 5V, and 50ma of 3.3V, Which is not very much. I expect you will have to provide external regulated voltage for your coil drive circuits.

Depending on the total power, you might just get by with a LM78xx and some simple NPN lowside drivers.

There are too many unknowns for me to speculate any farther.

Chuck.