Assignment :

Group assignment:
• probe an input device's analog levels and digital signals
Individual assignment:
• measure something: add a sensor to a microcontroller board that you have designed and read it

Week 11 learning journey :

Main goal for this week is to design and fabricate a microcontroller board with an input device/sensor, capturing the data with the input device and reading it. In addition, using an oscilloscope to perform some measure of the signal.

A sensor is simply defined as a device that is able to interact or senses changes in the external physical environment (temperature, motion sensor, etc) and capture reading from it.
Learning for this week :

• understanding of functioning of input devices (datasheet, etc)
• Programming the board to capture data and sending data to the computer
• Python programming to read from serial port
• Probing the input device's analog levels and digital signals

Reading datasheet of HC-SR04 Ultrasonic Sonar Distance Sensor

I choose the HC-SR04 Ultrasonic Sonar Distance Sensor as my input sensor module out of the many sensors that was in the Arduino development kit. This is the first time I am using an input sensor.

The HC-SR04 ultrasonic sonar distance sensor is able to measure distance from about 2cm to 400cm away (max range up to 3m, 10cm to 250cm for best result).




The first step is to look at the datasheet of the Ultrasonic Sonar Distance Sensor.

After some searching for the datasheets online, the datasheets available online are quite brief or lack much details about its internal working. However there are many online user guides written by other people on the use of this sensor.

From the datasheet :
1) A short pulse of at least 10μs (HIGH level signal) is supplied to the trigger input to start the ranging.
2) The sensor convert electrical signal to ultrasound. It emits an ultrasound at 40kHz (eight cycles of sonic bursts at 40 kHz) through the air via its two 'eye-like' shaped transmitter/receiver.
3) If the ultrasound hit an object along it path, the ultrasound will bounch back to the sensor, through HIGH level. The ECHO pin will goes HIGH for a period of time from the sending ultrasonic (uS) wave to returning. Another way of explanation, is ECHO Output pulse to microcontroller, width is the time from last of 8 40KHz bursts to detected reflected signal (microcontroller Timer gate signal)
4) The distance of an object can be calculated through the time interval between sending trigger signal and receiving echo signal. Therefore formal is as follow : is as follow :
     Test distance = (high level time × velocity of sound (340M/S) / 2, or
     uS / 58 = centimeters or
     uS / 148 = inch
Note: us equal μs (microsecond), a ASCII character u is used to indicate micro in place of μ




References :
- HC-SR04 Datasheet
- https://www.mpja.com website : HC-SR04 User Guide

Testing of sensor using Arduino UNO board

The next step is to test my sensor to see if it is working properly. I tested on a 'working reference board' (which is my Arduino UNO board) to understand how the sensor work, what the input require and output generated, as well as the accuracy of the output. I followed a sample Arduino code online to test it out.

References :
- Complete Guide for Ultrasonic Sensor HC-SR04 with Arduino

Electronic Design :

I made reference to Neil's board design. and attempted to replace the ATTiny45 chip with ATTiny44A, as it offered more PINs. So I drew a new board design. I hoping this board with more pins can also be used for next week Output Devices assignment and my Final Project.


At first, it was hard to 'wiring up' the components in EAGLE board design editor. I tried a few times, going to-and-fro between the schematic and board design to make changes. Later on, I resorted to making reference to my 'hello world' design and finally was able to design my 'Hello HC-SR04' board.

Neils' 'Hello HC-SR04' board : The pin connections on ATTiny45

My 'Hello HC-SR04' board : The pin connections on my ATTiny44A

3) My Schematic design
Placing a small 1uf Capacitor after VCC and before resistor and the microcontroller to act as a filter. A 10 Ohm pull-up resistor. A 0 Ohm resistor just for running a trace underneath.

Electronic Production : Milling and Stuffing my Ultrasonic Sensor Board

Programming my ultrasonic sensor board

I referred to this online guide for Ultrasonic Sensor HC-SR04. The original code is meant for Arduino Uno board, however I modified to apply the code to my self-designed 'Hello HC-SR04' board. I modified the Pins, changed the formulas for calculating the 'cm' and 'inches' by following the datasheet formula, and have my board sending the output data to the computer over the FTDI Pins.

References :
- Complete Guide for Ultrasonic Sensor HC-SR04 with Arduino


I mapped ATTiny44 'Echo' and 'Trigger' pins with Arduino PIN number by referring to the 'Arduino and ATTiny Pin Layout Diagam' posted on www.electrodragon.com website..



My code :

Note :

Uploading my code to my 'Hello HC-SR04' Board

I compiled and uploaded my code using Arduino IDE using a commercial USBAsp ver 2.0.

Installing Python and 'pySerial' package

I am new to Python and here are the steps to install Python and pySerial.
1) Download Python 3.7.3 64-bit from Python website. During install, tick the box "Add Python 3.7 to PATH"
2) Open Windows command prompt in Administrator Mode and run the command "pip install pyserial". The pySerial package is an add-on and allow Python to import the 'serial' library.
3) Open Python IDLE
4) Add in "import serial" into your code to import the 'serial' library.

My first Python code

I am new to Python programming and after hearing Python mentioned a couple of time during lesson, therefore I would like to explore on it. In the future, I hope to be like Neil to create UI (User interface) using python.

My FTDI connector is detected as 'COM4' port.
  


My simple Python code to read in the data from the ultrasonic input device :

#
#  Title: Ultrasonic_sensor.py
#  Author: Lucas Lim
#  Date Created: 2/4/2019
#  Last Modified: 4/4/2019
#  Purpose: To read data from Ultrasonic Sensor board
#


#import serial library
import serial

#open serial port
ser = serial.Serial('COM4', 9600)

# displayed serial port info
print (ser)

# displayed data read from from COM port
while True:
     print ((ser.readline()).decode('utf-8'))
  

void loop() {
  // The sensor is triggered by a HIGH pulse of 10 or more microseconds.
  // Give a short LOW pulse beforehand to ensure a clean HIGH pulse:
  digitalWrite(trigPin, LOW);
  delay(500);
  //delayMicroseconds(5);
  digitalWrite(trigPin, HIGH);
  delay(500);
  //delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
...
  //delay(250);
}