Pcf8575 problem [SOLVED]

[Fernando Garcia]

Hi!

Show me the schematic of your PCB.

Also make sure that the GND from Relay board is connected to Arduino GND.

Best regards.

[Gio Ricciardi]

Hi Fernando,
I forward you the schematic of the board.
The strange thing is that with a pcf8575 module everything work and with the other not.
at the moment I'm feeding the relays with the arduino's 5v and gnd.

the difference I notice between the two modules that the working one has an integrated resistor

thanks a lot

[Fernando Garcia]

Hi!

You can't feed relays using Arduino 5V, there's no enough current for it.

You should use an external power supply.

Best regards.

[Gio Ricciardi]

Hi Fernando,
Unfortunately even feeding the relay separately (gnd common) the pcf8575 sparkfun style does not work while the other is fine.
I ordered another to try if what I have is faulty but I don't think so
Do you think the schematic is correct?
Thank you again!

[Fernando Garcia]

Hi!

Schematic seems correct to me.

Best regards.

[Roch Mesa]

Hi...i haven't looked at this ic before but scanning the datasheet in a minute it looks like this chip does NOT have any registers or commands for reading back the written data. You can only use it to write data to the ports or read data from the ports (if you made them logic 1 on forehand). So no you can not read back data you earlier sent.

[Fernando Garcia]

Hi!

Welcome Roch!

Gio, the problem was solved?

Have you tested with new module?

Best regards.

[Gio Ricciardi]

hi Fernardo!!

unfortunately not.
I also tried the new pcf8575 but it gives the same problem.
the relay lights on dimly and doesn't work.
with the other pcf8575 everything works perfectly (https://www.ebay.com/itm/PCF8575-16-bit ... Swqlha-Pgs).
I really can't understand what the problem is...

[Fernando Garcia]

Hi!

Can you show me some pics?

Best regards.

[Jose Zazo]

Apologies for intruding on the thread, but the same thing happens to me.

With this type of module (PCF8575) the leds of relays are weakly illuminated but are not able to activate the relays.

I have now requested the model that indicates Gio (PCF8575 2) to test if this works, the bad thing is that the design of my PCB is for the model that in principle does not work.

As soon as I arrive and can try confirm the module.

Regards,

[Fernando Garcia]

Hi!

If do you have problem yet can you answer my last question?

I thought the problem was solved.

Best regards.

[Jose Zazo]

Sorry, I was still doing tests, the voltage was about 0.37 v and continued with the same problems. I used another 5v relay module and another PCB with a different PCF8575 and still had the same problems. I had left it as impossible and decided not to use the PCF module even if I limited some of the functionalities.

As soon as the new module that Gio indicated that it worked for me, I will try and comment on it.

Regards,

[Fernando Garcia]

The voltage should be around 1.5 V with ULN connected.

Disconnect the ULN and measure the voltage. It should be 5V.

Maybe the input voltage on PCF is less than 5V.

[Fernando Garcia]

Hi!

Any news here?

Best regards.

[Fernando Garcia]

Hi!

Any news here?

Best regards.

[Gio Ricciardi]

Hi Fernando,
Unfortunately not.
I've tried several PCF8575 cards but none goes.
With this model (https://m.geekbuying.com/item/OPRN-SMAR ... 82026.html) everything works fine even though I am very uncomfortable because I designed the card for the other PCF8575 model. The wiring is exactly the one indicated by you but without connecting the vdd and the gnd to the side of the board.
Best regards

[Fernando Garcia]

Hi!

Did you a shunts on bottom side to A0, A1 and A2?

It should be center to right (GND)

Did you a test with this module in a breadboard?

Best regards.

[Jose Zazo]

Apologies for entering the thread, as I said to me the same thing happens to Gio. Fernando seeing your answer I think the problem is due to the fact that A0, A1 and A2 are not welded with GND (the Sparkfun shield is the same as the photo you show). I understand that it is necessary to bridge by welding from the central point to the one on the left and free the one on the left at A0, A1 and A2. It is right?

Thank you

[Fernando Garcia]

Hi!

José, there's no problem to post here.

Your understanding is right.

I don't think it should be the real problem since when the signal is floating the module is found as 0x20 but just in case....

I would like to know if you and Gio can make this module work in a breadboard using LEDs in this way:

I think the module is working but there's no enough current to turn the relay ON.

The basic difference between blue and red module is the built-in 3.3 V regulator. Maybe when connected to 3.3V instead 5V the module can send more current to output pins.

Edit:

Now I found this video showing the red module working, so the problem should not be with this particular model.

Watch on youtube.com

Best regards.

[Jose Zazo]

At the moment I cannot test the assembly with LED's since I do not have them (I have ordered them).

As for the YouTube video, the same thing happens to me. The LEDs of the relays light up dimly but fail to trigger the relays.

Regards,

I have closed the thread I had open to continue in this since the problem is Gio and mine I think it is the same