Using a SN74HC595 Shift Register with Node JS

This project is the first step towards using the SPI with Onion Omega 2. It does not yet use SPI, only controls the shift register by simple GPIO commands.

Prerequisites on Omega 2

• Node JS (min. version: 4.0)

• Install Onoff Node

opkg update
opkg install onoff-node

Running the project

1. Upload the index.js file to your Omega 2.

2. Run the Node application

node index.js

Wiring

According to this wiring diagram.

Read more

• SN74HC595 data sheet
• Power dock spec
• Article on Bildr.org about the 74HC595
• Using the GPIOs on the Omega 2
• MediaTek MT7688 Datasheet

Using a SN74HC595 Shift Register with SPI & Python

This is the next level using the shift register. This time we are controlling it with the Omega's SPI module.

Prerequisites on Omega 2

• Python

• SPI Python Module

opkg update
opkg install python-light pyOnionSpi

• GPIO multiplexing setup properly

omega2-ctrl gpiomux set spi_cs1 spi_cs1
omega2-ctrl gpiomux set spi_s spi_s
# verifiy with the command below
omega2-ctrl gpiomux get

Note: You will not be able to use GPIO 6-9 as standard GPIOs until you set this back to GPIO mode. Read more here.

Running the project

1. Upload the index.py file to your Omega 2.

2. Run the Python application

python index.py

You will see the binary counter working (see the LEDs) and reading the last input back from the shift register (on the console).

Wiring

According to this wiring diagram.

Read more

• SN74HC595 data sheet
• Power dock spec
• Multiplexed GPIOs
• SPI Python Module
• MediaTek MT7688 Datasheet

Cheat sheet

# Read the direction for pin 7
fast-gpio get-direction 7

# Read the value of pin 7
gpioctl get 7
# or
cat /sys/class/gpio/gpio7/value

# Set the value for pin 7 and the direction to `output`
fast-gpio set 7 0

# Read the multiplexing setup
omega2-ctrl gpiomux get