Adafruit PCF8574 I2C GPIO Expander Breakout
Pimoroni
£4.25
Expand your project possibilities, with the Adafruit PCF8574 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 mill
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