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Pcf8575 problem

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Post Number:#1 Post Tue Feb 26, 2019 7:18 pm
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Hi Fernando
I have two pcf8575 modules.
https://www.ebay.com/itm/PCF8575-I2C-IO ... SwBPxcb6Qq
The first is this and everything works perfectly.
https://www.ebay.com/itm/PCF8575-16-bit ... Swqlha-Pgs
This is the second but even if it is correctly identified (0x20) it can not make the relays work. The leds are barely visible when turned on. The wiring is like the one you indicated with 10k resistances between sda/5v and scl/5v.

I would like to use the latter pcf8575 because I have already printed the board
Thanks

Post Number:#2 Post Wed Feb 27, 2019 8:13 pm
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Hi!

Show me the schematic of your PCB.

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

Best regards.
Please do not PM me for support unless it is absolutely necessary.

I'll not write custom function to nobody unless you can pay for my job.

Post Number:#3 Post Thu Feb 28, 2019 5:55 am
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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

Image


Image

Post Number:#4 Post Thu Feb 28, 2019 10:19 am
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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.
Please do not PM me for support unless it is absolutely necessary.

I'll not write custom function to nobody unless you can pay for my job.

Post Number:#5 Post Sat Mar 02, 2019 10:46 am
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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!

Post Number:#6 Post Sat Mar 02, 2019 1:04 pm
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Joined: Mon Mar 03, 2014 5:59 pm
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Hi!

Schematic seems correct to me.

Best regards.
Please do not PM me for support unless it is absolutely necessary.

I'll not write custom function to nobody unless you can pay for my job.




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