Multiple LEDs using fewer Pins- how to expand Arduino GPIO pins?

If you’re running low on GPIO pins, there are a few efficient methods you can use:

Shift Registers (e.g., 74HC595) – A shift register allows you to expand the number of outputs while only using a few GPIOs. With just three pins (Data, Clock, and Latch), you can control eight LEDs per shift register, and you can daisy-chain multiple registers to control even more LEDs. This is a great solution if you need simple on/off control for your LEDs.

Multiplexing – If you don’t need all LEDs to be on simultaneously, you can use a multiplexing approach. This involves arranging LEDs in a matrix where rows and columns are controlled separately, significantly reducing the number of GPIOs needed. However, since LEDs are turned on one at a time in rapid succession, brightness might be affected unless you use high-speed switching.

LED Driver ICs (e.g., MAX7219, TLC5940) – These chips are specifically designed for controlling multiple LEDs and even allow for dimming (PWM control). The MAX7219, for example, can control up to 64 LEDs using just three GPIOs (SPI interface). If you need PWM control for each LED, the TLC5940 is a great option.

I2C Expanders (e.g., PCF8574, MCP23017) – These chips expand the number of available I/O pins using I2C, meaning you only need two GPIOs (SDA and SCL) to control multiple outputs. They work well for LED control if you don't need high-speed switching.

Which method is best depends on your needs. If you just need simple LED control, a shift register is a solid and affordable choice. If you want PWM dimming or advanced control, an LED driver IC might be better. And if you need more general-purpose I/O expansion, I2C expanders could be the way to go.