I have two PCF8575 breakout boards that I would like to connect to my Raspberry Pi 3B+ running Debian Buster kernel version 4.19.75-v7. Since both have the same address (0x20), I need to create a new I2c bus or change the address of one of the PCF8575's. I have read that soldering a jumper wire from ground to one of the pads on the bottom side of the PCF8575 breakout board would accomplish this.

After cutting a resistor leg and using that as a jumper wire from ground to the right-most A2 pad, the hardware address seems to flip-flop on the Raspberry Pi. IE, sometimes it will show as 0x20, 0x24, 0x25, 0x27 when performing watch -n1 'sudo i2cdetect -y 1' on the Pi.

Has anyone else had a similar experience when trying to change the hardware address of an I2C device?

Edit: Here are pictures of the front and back of the breakout board: https://imgur.com/a/Gw9LbNv.

  • Not all I2C devices allow for a change of address. Even if they do they may be built in to a module which does not allow for a change of address. We need clear photos of the breakout board you are using. – joan Dec 11 '19 at 12:42
  • @joan - I have added a link to pictures of the front and back of the breakout board I am using. – Kris Dec 11 '19 at 13:57
  • Hi @Kris, Welcome and nice to meet you. I guess the three groups of three pads are used this way: One group is for A0, one group is for A1, and one group is for A2. Take A0 group for example. The middle pad is connected to the real pin A0. The pad on the left is connected to pulled down Vcc, the pad on the right is connected to pull up ground (or vice versa). You can use a multi-meter to measured the voltage level of the left/right pads. So if you connect A0 to the left pad, using a big solder blob, then A0 would be ground, (or high). This is sort poorman's jumper, I think. – tlfong01 Dec 11 '19 at 15:01
  • Actually you can see from the traces that all the three left pads are connected together. So my second guess is that the each of the middle pads have a 10k connected to Ax. And all three right pad are connected to Vcc (or Ground). No guarantee that my suggestion won't melt down something! :) Good luck and cheers! – tlfong01 Dec 11 '19 at 15:05
  • @tlfong01 - Wow, that is obvious now looking at it. I did disconnect the breakout board and put my mulitmeter in diode mode. The left pad in the group goes to vcc and the right pad goes to ground. I put a solder blob on the A1 group joining the left and middle pads. I am consistently seeing 0x22 as an address. Thank you for your help! – Kris Dec 11 '19 at 15:32

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