Review on HiLetgo PCF8574 PCF8574T IO Expansion Board I/O Expander I2C Evaluation Development Module (2pcs) by Eric Rose

GPIO pins are generally in short supply on most microcontrollers. These boards are a great way to add some 8-bit I/O ports to your device. I had a base address of 0x20, apparently some have a base address of 0x38. If in doubt, the code for the I2C scanner is easy to find. You can also just try 0x20 and if that doesn't work try 0x38. These devices can be easily cascaded, one device can be connected to a second (or third or fourth) up to eight. Of course you need to install address jumpers so that each board has a unique address; If your board's base address is 0x20, you can use jumpers to set it to 0x21, 0x22, .0x27. One thing I found is that it would make sense to add your own pull-up resistors to SDA and SCL. The 4.7 kΩ resistor works well. Excellent value for money and quality.