Using a PCF8575 and a PCA9685 together

Projects General Guidance
1

Has anyone used these two together wanting switches on the PCF pins to operate Servos on the PCA. I am using the Adafruit libraries and for some reasons when I try to set the PWM frequency the Arduino appears to reset.

If you have a working sketch I would appreciate a copy.
Thanks
Terry

2

They work together just fine. Post your annotated schematic that shows exactly how you have wired this. Show all power, ground, power sources, and any other hardware connected to it.

3

I'm sorry I don't have the necessary software to draw a schematic I can post. Simply to say though I have wired the GND, VCC SDA and SCL from the pins of the Uno to the pins on the PCA board and from the other end of that board direct to the PCF. If I load a sketch that just drives the PCF then that works fine, and if I load a sketch that just drives the servos, that works fine. It is just when I try to combine the two.
Thanks
Terry

4

Upi can use KiCad, it is free. They will ask for a donation but it is not required. It if a great CAD (Computer Aided Design) package. Try to post your sketch as well.

5

A photo of a pencil/paper drawing will be fine. Don't forget all power connections as well.

6

Run the I2C_scanner example sketch and see if it finds both devices.
One is at address 0x20 and the other at 0x40.

7

It sounds like a fault in your code. Please post it. Use code tags as described in the forum guide.

Have you successfully tested code which sets the PWM frequency when the PCF is not connected or not used?

8

yep it finds the devices on 0x21 (the PCF and yes I have set the correct address in the sketch) and 0x40 for the PCA.

9

Then as @PaulRB suggested there is probably are error in your code where you attempted to combine the two functions.
You need to post your code. In the IDE click on Edit then Copy for Forum, that will copy your code, then come back here and just do a simple paste.

10

Sorry I have not replied before as i have been away for a few days.
I seem to have narrowed the problem down to incompatability between the Adafruit PWM library and the Adafruit PCF8575 library. It may be because both attempt to create the Wire object and start it.
I removed the PCF8575 library and drove the wire interface directly for the PCF8575 device assuming that the PWM library initialised it and everything works fine.
It is bad design that both libraries try to create and initialise the wire object.
Thanks for all the info
Best Wishes
Terry