This document provides information about a workshop on mruby and embedded systems being held from September 11-15, 2023. The workshop will cover topics including mruby programming for small devices, controlling circuits with a microcontroller board, and using sensors like a brightness sensor. Attendees will learn to program an LED to blink and change brightness using mruby code, and will interface a CdS brightness sensor with a microcontroller to control an LED based on light levels. The workshop aims to give experience in embedded software development and interacting with electronic components like LEDs through programming.

1. Workshop
Kyushu Institute of Technology
Kazuaki Tanaka
2023/9/11-2023/9/15

2. About Me
• Kazuaki TANAKA（たなか かずあき）
• Kyushu Institute of Technology, JAPAN
Associate Professor
• Ph. D in Information Science
• Research topics: embedded systems, IoT,
mruby, wireless communication

3. Research topic:
mruby and mruby/c
• Ruby language for small devices
• OO Programming Language
• Target: one-chip microcontroller
PIC, ESP32, STM32, etc.
• Small memory footprint
minimum 20KB
• Open-Source Software
https://github.com/mruby/mruby
https://github.com/mrubyc/mrubyc

4. What is Ruby language?
• Object Oriented Programming Language
– Scripting language
– Web application, Ruby on Rails
• Matsumoto has said that Ruby is designed
for programmer productivity and fun.
led1 = GPIO.new(0)
while true do
led1.write 1
sleep 0.5
led1.write 0
sleep 0.5
end
Ruby code example:

5. Research topic:
wireless communication
• LPWA(Low Power Wide Area) communication
network

6. LPWA
• Long range wireless communication
– ~10km by small wireless module
– Using 920MHz band
24mm
17mm
Low power
Tx: 43mA
Rx: 20mA
Sleep: 1.7μA
Speed:
1kbps

7. Introduction

8. This workshop
• Experience in embedded software
development.
• mruby programming
• Controlling electronic circuits
• Brightness sensor

9. Simple Circuit

10. Electrical circuit
• Micro controller board
• Electrical parts and circuit
– LED, sensors
– Breadboard
(prototyping board)

11. Run the first program
• Coding
• Compile and Download
Download= transfer compiled program into
microcontroller board
• Execute

12. Programming environment
• Open following URL
or
https://mrubyc-ide.ddns.net/editor/rboard
https://bit.ly/45InC1H

13. Blinking LED
• program1
• First, run this program
led1 = GPIO.new(0)
while true do
led1.write 1
sleep 0.5
led1.write 0
sleep 0.5
end

14. Microcontroller board
• RBoard
• Features
– Execute program
– Store data
– I/O of Pins
– Input= Measure voltage
– Output= Set voltage
HIGH(1) or LOW(0)
Pin

15. Onboard LEDs
• 4 LEDs, each LED is connected to Pin
– LED 1: Pin 0
– LED 2: Pin 1
– LED 3: Pin 5
– LED 4: Pin 6
• Set pin voltage to HIGH, then turn on LED
Set to LOW, then turn off LED

16. Program
• GPIO： General Purpose Input and Output
led1 = GPIO.new(0)
while true do
led1.write 1
sleep 0.5
led1.write 0
sleep 0.5
end
Pin0 is assigned to variable led1
Iteration
write: set voltage
sleep: stop execution

17. Exercises
• Blink two LEDs alternately
• Blink four LEDs
LED 1: Pin 0
LED 2: Pin 1
LED 3: Pin 5
LED 4: Pin 6

18. LED
• Light Emitting Diode
Current flows from Anode to Cathode
Longer: Anode
Anode Cathode

19. LED Circuit
• Make LED on
– Current flowing through the LED
• Rboard feature
– Set voltage of Pin
– Set HIGH or LOW

20. Wrong circuit
Board
Pin (HIGH)
Pin (LOW)
LED
The resistance of LED is almost 0.
Many current flows,
cause damages to LED

21. LED circuit
Board
Pin (HIGH)
Pin (LOW)
LED
Resistor
1K ohm
Resistor limits current flowing.

22. LED circuit
Board
Pin (HIGH/LOW)
GND
LED
Resistor
1K ohm
GND is always LOW
LED on if Pin is HIGH
LED off if Pin is LOW

23. Breadboard
(Prototyping board)
• Red holes are connected

24. Using breadboard
• Connecting a LED and a resistor
LED
Resistor
Longer leg Shorter leg

26. Connecting
• Use jumper wires
Pin 15
GND
LED
Resistor
Pin １５
GND

27. Implement your code
led1 = GPIO.new(15)
led1.setmode(0)
while true do
led1.write 1
sleep 0.5
led1.write 0
sleep 0.5
end
Set pin mode
0: Output voltage
1: Input voltage
Pin 15

28. Exercises
• Blink several LEDs on breadboard
You can use Pin15, Pin16, Pin17, Pin18, Pin19, Pin20

29. PWM

30. PWM
Analog output
• Output of microcontrollers: Digital
– HIGH or LOW voltage
– In LED, ON or OFF
• We want: Analog
– Change voltage
– In LED, ON…bright…dark…OFF

31. Pseudo analog output
• PWM, pulse width modulation
• Control HIGH and LOW rapidly
– 1000 times a second
0.1 msec.
50% HIGH 50% LOW

32. Change brightness
• Change brightness => Change duty ratio
Time
1 msec.
Duty=1
Duty=2
Duty=1023
Duty=1022
Duty=1
Duty=0
Duty=0

33. PWM example
led1 = PWM.new(15)
led1.frequency 10000
while true do
for i in 0..1023 do
led1.duty i
sleep 0.001
end
for i in 0..1023 do
led1.duty 1023-i
sleep 0.001
end
end
duty: 0 to 1023
0: 0% HIGH
1023: 100% HIGH

34. Brightness Sensor

35. CdS
• CdS: Resistance changes with varying light
levels.
• Microcontroller can detect VOLTAGE

36. CdS circuit
CdS
3.3V
Pin20
GND
Resistor
1K ohm
R ohm
Bright: small R
Dark: large R
𝑃𝑖𝑛20 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 = 3.3 ×
1𝐾
1𝐾 + 𝑅

37. 3.3V
Use this Pin

38. ADC
• ADC: Analog Digital Converter
– Read voltage at Pin20
– Voltage v
0 < v < 1.5
adc = ADC.new(20)
v = adc.read

39. CdS example
led1 = GPIO.new(0)
adc = ADC.new(20)
while true do
v = adc.read
if v<0.5 then
led1.write 1
else
led1.write 0
end
sleep 0.1
end
Read voltage
from Pin20
Voltage: 0 < v < 1.5
Pin20 for ADC

40. Exercises
• Brightness sensor
• LED changes by brightness
– Green: bright
– Yellow: a little dark
– Red: dark
• adc.read returns around 0.2 in dark, and
returns around 0.9 in bright

41. Conclusion

42. Embedded systems
• Software and Hardware integration
• Software controls hardware
– Requires both software and hardware knowledge