You just found the perfect I2C sensor, and you want to wire up two or three or more of them to your Arduino when you realize "Uh oh, this chip has a fixed I2C address, and from what I know about I2C, you cannot have two devices with the same address on the same SDA/SCL pins!" Are you out of luck? You would be, if you didn't have this ultra-cool CJMCU-9548 1-to-8 I2C multiplexer!
Finally, a way to get up to 8 same-address I2C devices hooked up to one microcontroller - this multiplexer acts as a gatekeeper, shuttling the commands to the selected set of I2C pins with your command.
Using it is fairly straight-forward: the multiplexer itself is on I2C address 0x70 (but can be adjusted from 0x70 to 0x77) and you simply write a single byte with the desired multiplexed output number to that port, and bam - any future I2C packets will get sent to that port. In theory, you could have 8 of these multiplexers on each of 0x70-0x77 addresses in order to control 64 of the same-I2C-addressed-part.
Like all Adafruit breakouts, we put this nice chip on a breakout for you so you can use it on a breadboard with capacitors, and pullups and pulldowns to make usage a snap. Some header is required and once soldered in you can plug it into a solderless-breadboard. The chip itself is 3V and 5V compliant so you can use it with any logic level.
Pinouts:
Power Pins:
- Vin - this is the power pin. Since the sensor chip uses 3-5 VDC. To power the board, give it the same power as the logic level of your microcontroller - e.g. for a 5V micro like Arduino, use 5V
- GND - common ground for power and logic
I2C Control-Side pins:
- SCL - this is the I2C clock pin for the chip itself, connect to your microcontrollers I2C clock line.
- SDA - this is the I2C data pin for the chip itself, connect to your microcontrollers I2C data line.
- RST - this is the reset pin, for resetting the multiplexer chip. Pulled high by default, connect to ground to reset
- A0 A1 A2 - these are the address selection pins for the multiplexer. By default the multiplexer is at address 0x70 and these three pins are pulled low. Connect them to Vin to set the address to 0x71 - 0x77.
- A0 is the lowest-significant bit (if it is pulled high, it will increase the address by 1).
- A1 is the 2nd-lowest-significant bit (if it is pulled high, it will increase the address by 2).
- A2 is the 3rd-lowest-significant bit (if it is pulled high, it will increase the address by 4).
I2C Multiplexed-Side pins:
- SDx and SCx: There are 8 sets of SDx and SCx pins, from SD0/SC0 to SD7/SC7. These are the multiplexed pins. Each one is a completely seperate I2C bus set. So you have have 8 I2C devices with identical addresses, as long as they are on one I2C bus each.
These pins do not have any pullups installed, so if you are using a chip or breakout without i2c pullups be sure to add them! Nicely, you can have Vin be 3.3V and have these pins pulled up to 5V (that is, they are 5V compliant)
