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+--- Thread: B8M Schematic (/showthread.php?tid=8945)
B8M Schematic - mikkojay - 01-15-2026
Hello,
Is the schematic diagram available for the B8M?
I am specifically looking to see if the INT pin 1 of the PCF8575 is connected to anything.
I have used the PCF8575 IC in other applications, and prefer to use the interrupt when possible.
Thank You
RE: B8M Schematic - admin - 01-15-2026
PCF8575 INT pin not used. if you want to use , you can solder it to ESP32 free pin.
RE: B8M Schematic - mikkojay - 01-16-2026
So no schematic?
It looks like the pin 1 of the PCF8575 has a trace going to R80.
The other side of R80 looks to be tied to 3.3v as a pull-up.
Just checking.
Also, to find a convenient free IO pin, I noticed in the pin document page that it shows GPIO5 in two places:
SD Card:
SPI-MOSI:GPIO10
SPI-SCK:GPIO11
SPI-MISO:GPIO12
SPI-CS:GPIO9
SPI-CD:GPIO5
--------------------
RF433M sender:GPIO4
RF433M receiver:GPIO5
If this board does not use RF433M, should that mean that GPIO4 is really free?
Edit- looking at the ESP32 data sheet, it looks like pin 4 might not be a good choice anyway (strapping pin), looks like GPIO6 would be good.
Thank You
RE: B8M Schematic - admin - 01-16-2026
1. here is PCF8575 schematic.
2. sorry, B8M no RF433M resource, we have updated pin define, remove the RF433M module pin define.
3. why not use these free gpio?
GPIO13
GPIO14
GPIO21
they are ESP32 pin directly to use.
RE: B8M Schematic - mikkojay - 01-16-2026
Thank you very much!
Regarding the free gpio, yes- I will use one of the available pins.
I do need 3 pins (no pull-up) for use with a PCM5102a audio DAC module.
BCK, LCK, DIN signals.
I may use GPIO47.
I have a hot air SMD station, so I may just remove either R80 or R4 so I do not have 2x pull-up resistors.
R4 looks like it will be easiest.
Either way, I will need to use the microscope
Thank you again for your assistance.
RE: B8M Schematic - admin - 01-17-2026
you are welcome.