im, running out of pins

Using Arduino General Electronics
11

Tyre are various options once you start using up all pins.

  1. Move to another uC with more pins, such as 644P, 1284P or 2560.

  2. Put other devices on shared buses, such as I2C and SPI, to free up other pins. This can require use of port expanders such as the PCF8574 which gives 8 input/outputs for 2 shared pins on the uC.

  3. Use a voltage divided to read multiple buttons on an Analog pin. It needs tolerances building in and debouncing.

  4. Matrix buttons and make use of the Keypad library to give you up to 9 buttons on 6 pins, 16 on 4 pins, 25 on 5 pins etc. Upto 4 x 4 (8 pins) can also be used together with a PCF8574 and Keypad_I2C to get 16 buttons on 2 pins. This can be repeated on the same two I2C pins to have 32, 64, 128 buttons or more.

  5. Use cheap shift registers, such as the 8 bit 74HC595, and cascade to expand input/outputs using just 3 uC pins. limited only by the processing overhead to drive the number of shift registers you incorporate.