Embedded Systems and Software. Rotary Pulse Generators

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1 Embedded Systems and Software Rotary Pulse Generators Slide 1

2 What Is An RPG? RPG = Rocket Propelled Grenade RPG = Rotary Pulse Generator Slide 2

3 Rotary Encoders Switch Switch Output Quadrature output Slide 3

4 Rotary Encoder Applications Consumer Electronics User Interfaces Slide 4

5 Rotary Encoder Applications Multi-axis Robot Arms From Analog-Digital Conversion Handbook, Analog Devices, 3 rd Edition. Prentice Hall, Slide 5

6 Rotary Encoders Optical Encoders From Analog-Digital Conversion Handbook, Analog Devices, 3 rd Edition. Prentice Hall, Slide 6

7 Rotary Encoders Optical Encoders From Analog-Digital Conversion Handbook, Analog Devices, 3 rd Edition. Prentice Hall, Slide 7

8 Simple Rotary Encoder Internals c Slide 8

9 Simple Rotary Encoder Internals Both switches closed Both switched open, normally at detent Slide 9

10 Electrical Connections Test circuit, from the data sheet Pullup resistors Low-pass filter Low-pass filter Remember contact bounce? Slide 10

11 Terminology 90 Phase shift quadrature output 1-cycle, corresponds to a turn from one click/detent to another Number of pulses per revolution depends on particular device. Common numbers are 4, 6, and12, but some has as many as 6,000 ($$$) Slide 11

Panasonic EVE-GA1F2012B Encoder Cost: ~ $0.

12 Panasonic EVE-GA1F2012B Encoder Cost: ~ $ detents, positions What is a detent? Data sheet does not explicitly specifies maximum rpm, but implies that it is 60 A C B Quadrature output Slide 12

13 Opening Up An Encoder Inside the top of the rotary encoder case is a metal disc spring (also called a spring washer) with small raised areas. The disc of the encoder shaft is impressed with ridges that rub against the bumps in the spring to make clicking sounds as the shaft is turned. Credits: Slide 13

14 Opening Up An Encoder Credits: Slide 14

15 Signals with pull up resistors, and single detent-detent CW turn Slide 15

16 EVE-GA1F2012B Timing Diagram From the datasheet = 1 revolution/sec Note Slide 16

17 EVE-GA1F2012B Timing Diagram Note at detent steady point, both switches are open (and output pulled high), and the pulse width depends on how fast the RPG is turned. User is turning RPG slow User is turning RPG faster Slide 17

18 EVE-GA1F2012B Timing Diagram Note at detent steady point, both switches are open (and output pulled high), and the pulse width depends on how fast the RPG is turned. Detend Positions Slide 18

19 EVE-GA1F2012B Timing Diagram Note that between detents, both switches are open or off, and the pulse width depends on how fast the RPG is turned. Detend Positions Slide 19

20 EVE-GA1F2012B Specifications Contacts may bounce during transitions. This can cause erroneous readings Slide 20

21 Electrical Connections Test circuit, from the data sheet Pullup resistors Low-pass filter Low-pass filter Remember contact bounce? Slide 21

22 Review: Gray-Code The reflected binary code, also known as Gray code after Frank Gray, is a binary numeral system where two successive values differ in only one bit. Dec Binary Gray Slide 22

23 Gray-Code Output AB 01 Slide 23

24 Gray-Code Output AB 00 Slide 24

25 Gray-Code Output AB 10 Slide 25

26 Gray-Code Output AB 11 Slide 26

27 Gray-Code Output AB 01 Cycle starts again Slide 27

28 Gray-Code Output AB Gray-code sequence, repeats 12 times per revolution for the EVE-GA1F2012B encoder used in Lab 3 Slide 28

29 Reading Encoder Output A B How fast should we read the encoder outputs so that we don t miss a transition? Answer: 5 ms if we sample at A and wait longer than B, we will miss a transition Slide 29

30 Possible RPG Connection to ATtiny45... cbi DDRB,0 cbi DDRB,1... SBIS PINB,0... This instruction tests a single bit in an I/O register and skips the next instruction if the bit is set. For input use PINB, not PORTB Rotary encoder Slide 30

Detecting the Direction of Rotation Clockwise (positive) rotation pattern 00

31 Detecting the Direction of Rotation Clockwise (positive) rotation pattern Counter-clockwise (negative) rotation pattern Slide 31

32 Detecting the Direction of Rotation Clockwise (positive) rotation pattern = = = = Counter-clockwise (negative) rotation pattern = = = = Slide 32

33 Slide 33

Embedded Systems and Software

Embedded Systems and Software Notes on Lab 2 Embedded Systems in Vehicles Lecture 2-4, Slide 1 Lab 02 In this lab students implement an interval timer using a pushbutton switch, ATtiny45, an LED driver,