CMSC838 Week 15 | Lecture 27 | May 5, 2015 fileWeek 15 | Lecture 27 ... Scenario 2 Create the night rider example Scenario 3 Make a sensor-based bar graph where the LEDs represent

Human Computer Interaction Laboratory

@jonfroehlich Assistant Professor Computer Science

CMSC838 Tangible Interactive Computing

Week 15 | Lecture 27 | May 5, 2015 Using ICs to Expand Arduino Functionality

TODAY’S LEARNING GOALS

1. Learn about expanding Arduino’s capabilities using

ICs

2. Learn how use a common IC: 74HC595

3. Discuss Final Projects

Motivating Scenario

Imagine you need to light up five LEDs but only have one digital

I/O port remaining on the Arduino Uno. What do you do?

Motivating Scenario

Imagine you need to light up eight LEDs but only have three

digital I/O ports remaining on the Arduino Uno. What do you do?

Motivating Scenario

Imagine you need to light up eight LEDs but only have three

digital I/O ports remaining on the Arduino Uno. What do you do?

You could:

• Switch to an Arduino Mega

• Find a shield like a MUX Shield from Sparkfun that

expands your I/O ports

• Use a shift register IC!

USING THE UBIQUITOUS 74HC595 SHIFT REGISTER Night Rider Shift Register Example based on Chapter 7 of Jeremy Blum’s Exploring Arduino book

USING THE UBIQUITOUS 74HC595 SHIFT REGISTER Analog Read Shift Register Example based on Chapter 7 of Jeremy Blum’s Exploring Arduino book

THE 74HC595 8-BIT SHIFT REGISTER

The 74HC595 is an 8-bit serial-in, parallel-out shift register. This means that you load the data into the

shift register serially but can output it simultaneously (using the clock line, the data line, and the latch)

[sources: Chapter 7 of Jeremy Blum’s Exploring Arduino book; https://learn.sparkfun.com/tutorials/shift-registers; https://www.sparkfun.com/datasheets/IC/SN74HC595.pdf]

THE 74HC595 8-BIT SHIFT REGISTER Understanding the DATA, the CLOCK, and the LATCH lines


The 74HC595 is a synchronous device. It only acts on the

rising edge of a clock signal. Every time the clock signal

transitions from low to high, all the values currently stored in

the eight output registers (memory) are shift over one

position.

The last output is either discarded or output on the QH’ pin if

you are cascading registers.

Simultaneously, the value currently on the DATA input is

shifted into the first position.

By doing this eight times, the present values are shifted out

and the new values are shifted into the register.

The LATCH pin can then be set to high to simultaneously

make the outputs appear.

74HC595 8-BIT SHIFT REGISTER EXAMPLE Let’s say that we want to load the ‘1010 1010’ into the shift register. Recall that the DATA line is only read on the CLOCK’s

rising edge and that the output registers are only loaded with these values when the LATCH signal goes HIGH.


74HC595 DATA SHEET https://www.sparkfun.com/datasheets/IC/SN74HC595.pdf

Pins QA through QH represent the eight parallel outputs from

the shift register

VCC will connect to 5V

GND will connect to shared ground with Arduino

The SER pin is the DATA input

The SRCLK pin is the CLOCK pin

The RCLK pin is the LATCH pin (also known as the register

clock pin as it allows you to ‘commit’ your recently shifted

serial values to the parallel outputs all at once)


https://www.sparkfun.com/datasheets/IC/SN74HC595.pdf


74HC595 DATA SHEET https://www.sparkfun.com/datasheets/IC/SN74HC595.pdf

Pins QA through QH represent the eight parallel outputs from

the shift register

VCC will connect to 5V

GND will connect to shared ground with Arduino



The RCLK pin is the LATCH pin (also known as the register

clock pin as it allows you to ‘commit’ your recently shifted

serial values to the parallel outputs all at once)

You will not be using the SRCLR or OE pins but; however, for

comprehensiveness:

OE stands for output enable. The bar over the pin name

indicates that it is active low. When the pin is held low, the

output is enabled. In our example, we will tie this to ground.

SRCLR is the serial clear pin. When pulled low, it empties the

contents of the shift register. For our examples today, we will

tie it directly to 5V from preventing our values from being

cleared.




IN-CLASS EXERCISES

Scenario 1

Simply load a bit value into the shift register and represent it via an LED array

Scenario 2

Create the night rider example

Scenario 3

Make a sensor-based bar graph where the LEDs represent the sensor’s value.

Scenario 4 (if time)

Work with a partner to cascade your two shift register circuits together using

one Arduino and still just three wires (this doubles the number of outputs while

using the same number of pins on the Arduino)

BASIC WIRING DIAGRAM




The RCLK pin is the LATCH pin (also known as the register clock pin as it allows you to ‘commit’ your recently shifted serial values to the parallel outputs all at once)

SCENARIO 1


SCENARIO 2 Night Rider with Pre-Computed LED Values


SCENARIO 2 Night Rider with Bit Shifting


SCENARIO 3 Sensor bar graph


HELPFUL RESOURCES

http://www.arduino.cc/en/Tutorial/ShiftOut

https://learn.adafruit.com/adafruit-arduino-lesson-4-eight-leds/other-things-to-do

Chapter 7 “Shift Registers” in Jeremey Blum’s book Exploring Arduino






















http://www.cs.umd.edu/class/spring2015/cmsc838f-sp15/protected/Blum_ExploringArduino_Chapter7_ShiftRegisters_1stEdition_2013.pdf

Documents

CMSC838 Week 15 | Lecture 27 | May 5, 2015 fileWeek 15 | Lecture 27 ... Scenario 2 Create the night rider example Scenario 3 Make a sensor-based bar graph where the LEDs represent