search

RobTillaart / I2CKeyPad

Arduino library for 4x4 (or smaller) keypad connected to an I2C PCF8574.
MIT License
49 stars 9 forks source link

I2CkeyPad and PCF8575 not working together #21

Closed ennio64 closed 3 months ago

ennio64 commented 4 months ago

I2CKeyPad version=0.4.0 and PCF8575 version=0.2.3 not working together. On stm32f411 individually they work well but together on the same bus they conflict. I change the I2C bus for pcf8575 (use I2C3 SCL=PA8 and SDA=PB4) TwoWire myWire(PB4, PA8); PCF8575 PCF8575A(0x20, &myWire); and work.

RobTillaart commented 3 months ago

Sorry for the long delay, I missed the notifications.

RobTillaart commented 3 months ago

@ennio64

The possible I2C addresses of the PCF8574 and the PCF8575 do overlap. So you should not use the same (default) addresses for both.

Have you tried to give the PCF8574 and the PCF8575 different addresses?

Another option is to use a PCF8574A for the keypad as this has another address range.

RobTillaart commented 3 months ago

Will add a section to the readme.md file like this

I2C addresses

This library uses a PCF8574 or a PCF8574A chip. These devices are identical in behavior although there are two distinct address ranges.

Type Address-range Notes
PCF8574 0x20 to 0x27 same range as PCF8575 !
PCF8574A 0x38 to 0x3F

@ennio64

Is the problem still actual?

RobTillaart commented 3 months ago

Created develop branch with new readme.md

ennio64 commented 3 months ago

Not is a addresses conflict, when I tried both on the same I2C bus they had different addresses and conflicted. In my project I solved it by using two different I2C buses.

RobTillaart commented 3 months ago

@ennio64 I understand that using two I2C busses works as you separate the devices.

If I recreate the setup of an PCF8574 and PCF8575 on one bus I see two different I2C addresses. (using different addresses by means of the A0, A1 and A2 pin, and pull up resistors on SDA / SCL of course). So I do not understand how your conflict looks like? Did you see only one I2C address? did you get a lot of read failures? How did the conflict expose itself?

If you have time, can you please elaborate on this? If no time, no problem, then I just close the issue.