5545-ADA, Adafruit PCF8574 I2C GPIO Expander Breakout - STEMMA QT / Qwiic

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US$7.23
5545-ADA
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The ADAFRUIT 5545 is a GPIO Expander Breakout - an affordable 8-channel I2C expander.

GPIO expanders work like this: you have a board with some number of GPIO but not enough for your project - maybe you need more buttons or LEDs. You could upgrade to a board with massive number of GPIO like the Grand Central, or you could pop on one of these boards. Connect it over I2C and then you can send/receive I2C commands to control the GPIO pins to write and read them. It's going to be slower than direct GPIO access, but maybe that doesn't matter if it takes a millisecond instead of a microsecond. You only need the two I2C pins, and you can even share the I2C port with other sensors and devices. Heck, you can even add more expanders for massive I/O control!

  • It has 8 I/O pins
  • Three I2C address select jumpers mean up to 8 expanders to one bus for 64 total GPIO added
  • Each pin can be an input with light pull-up or an output sink
  • IRQ output will automatically alert you when input pins change value
  • This chip does not have a pin direction register. You cannot set the pins to be input or output - instead each pin has two possible states. Basically you can think of it as an open-drain output with a 100K resistor pull-up built in.
  • Option one: Lightly pulled up 'input' - by default it will read as a high logic level, but connecting the GPIO to ground will cause it to read as a low logic level.
  • Option two: Strong 20mA low-driving transistor sink output. This means the output is 'forced' to be low and will always read as a low logic level.
The only thing to watch for is you cannot drive an LED that is expecting the expander GPIO to go high to turn on the LED, or connect a button input to a positive voltage without adding an additional pull-down resistor. If this is a bit confusing, worry not - all this stuff is taken care of for you in the Arduino PCF8574 library or CircuitPython/Python PCF8574 library.

Technical Details

  • Product Dimensions: 25.5mm x 17.7mm x 4.6mm / 1.0" x 0.7" x 0.2"
  • Product Weight: 1.7g / 0.1oz
 
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