CMSC838. Tangible Interactive Assistant Professor Computer Science

Transcription

1 CMSC838 Tangible Interactive Computing Week 15 Lecture 27 May 5, 2015 Using ICs to Expand Arduino Functionality Human Computer Interaction Assistant Professor Computer Science

2 TODAY S LEARNING GOALS 1. Learn about expanding Arduino s capabilities using ICs 2. Learn how use a common IC: 74HC Discuss Final Projects

3 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?

4 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?

5 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!

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

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

8 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)

9 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.

10 74HC595 8-BIT SHIFT REGISTER EXAMPLE Let s say that we want to load the 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.

11 74HC595 DATA SHEET Pins Q A through Q H represent the eight parallel outputs from the shift register V CC 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)

12 74HC595 DATA SHEET Pins Q A through Q H represent the eight parallel outputs from the shift register V CC 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) 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.

13 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)

14 BASIC WIRING DIAGRAM 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)

15 SCENARIO 1

16 SCENARIO 2 Night Rider with Pre-Computed LED Values

17 SCENARIO 2 Night Rider with Bit Shifting

18 SCENARIO 3 Sensor bar graph

19 HELPFUL RESOURCES Chapter 7 Shift Registers in Jeremey Blum s book Exploring Arduino