PV198 - Analog to Digital
Conversion
One-chip Controllers
Dávid Danaj, Marek Vrbka
Faculty of Informatics, Masaryk University
Content
Content
Overview
Demo
Theory
Successive Approximation
Joystick
Application
Homework
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 2 / 23
Overview
Intro
Switch the branch!
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 3 / 23
Overview
What is ADC
ADC - Analog to Digital Converrter
Convert analog signal into digital values
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 4 / 23
Overview
What is it used for
Everything that needs to transfer analog values into digital
values
Audio
Sensors
Video
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 5 / 23
Demo
Demo - Heartbeat sensor
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 6 / 23
Demo
Demo - Heartbeat sensor
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 7 / 23
Theory
How does it work
https://www.allaboutcircuits.com/technical-articles/
understanding-the-dynamic-range-specification-of-an-ADC/
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 8 / 23
Theory
Sampling resolution
Smallest incremental voltage that can be recognized and thus
causes a change in the digital output
Expressed as the number of bits output by the ADC
https://www.electricaltechnology.org/2019/02/analog-to-digital-converter-adc.html
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 9 / 23
Theory
Quantization Error
Difference between analog value and rounded digital value
(rounding error)
Change in analog value smaller than the step of the digital value
is ignored
The quantization error is 0.5 least significant bit for the ADC
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 10 / 23
Theory
Sampling Rate
Nyquist-Shannon theorem
ADC sampling frequency must be at least twice the analog signal
frequency
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 11 / 23
Theory
Dynamic Range
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 12 / 23
Successive Approximation
Linear Successive Approximation Algorithm
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 13 / 23
Successive Approximation
Linear Successive Approximation Algorithm
Vin = 2.1V
Vref = 3.3V
3-bit resolution
Step Digital code DAC output
Output
Comparator
Digital
output
1 100 1.65V 1 1|00
2 110 2.475V 0 10|0
3 101 2.0625V 1 101
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 14 / 23
Successive Approximation
Linear Successive Approximation Algorithm
Vin = 1.16V
Vref = 3.3V
5-bit resolution
Step Digital code DAC output
Output
Comparator
Digital
output
1
2
3
4
5
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 15 / 23
Successive Approximation
FRDM-K66F ADC
Linear successive approximation algorithm with up to 16-bit
resolution
Single or continuous conversion
Can work in low-power modes
HW trigger to start conversion
HW average function
Conversion complete interrupt
DMA support
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 16 / 23
Joystick
Joystick
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 17 / 23
Joystick
Joystick
DO NOT USE 5V
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 18 / 23
Joystick
Joystick - Connection (Easy)
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 19 / 23
Joystick
Joystick - Connection (Difficult)
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 20 / 23
Application
Application
Tasks
Create an application that reads position of the joystick (both
axes) using ADC0 and ADC1
Print position to terminal
Write periodic check into while loop if measurement is finished
Use PIT to initialize read only once a second
Either
Write ADC read only using interrupts
React to joystick button press
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 21 / 23
Application
Steps
Initialize (MCUXpresso Configuration Tools might help here)
Pins
Clocks
Peripherals (configure ADC0 and ADC1)
Write application code
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 22 / 23
Homework
Homework - Use joystick to control LEDs
Only use ADC1 peripheral with multiple channels
Warning: ADC has special handling of interrupt flags
Use the same connection as shown in the difficult slide
PTB7 controls green LED, PTB6 controls red LED
D. Danaj, M. Vrbka ·PV198 - Analog to Digital Conversion · 23 / 23