Akila's week 11 at Fab academy

1. Group assignment: measure the analog levels and digital signals in an input device

1. The HC-SR04 ultrasonic sensor module which can emit ultrasound at 40000Hz. The wave travels through the air and on hitting an object, it bounces back to the module. The travel time and speed of the echo wave will help to calculate the distance of the object from the module.

2. 5V DC supply was connected to the VCC pin on the sensor.

3. The function generator was used to generate a signal of frequency 40000Hz and its ouput was connected to the Trig pin on the ultrasonic sensor.

4. The oscilloscope was connected to the Echo pin of the sensor to measure the returning pulse.

5. When the object is closer to the sensor, the pulse width is smaller, corresponding to the travel time taken by the echo signal.

6. The pulse width is larger when the object is further away from the sensor.

7. A sheet of thermocol is held above the sensor and its distance is varied to check the pulse width of the echo signal.

8. When the sheet is held closer to the sensor, the pulse width is smaller.

2. PCB production

I made a temperature sensing board. Neil had explained two types of temperature sensors - NTC (Negative Temperature Coefficient) and RTD (Resistance Temperature Detector). This page summarizes the differences between the two types of temperature sensors.

I tried making the NTC thermistor board, which, according to Neil, is preferred for lower temperature applications. I referred to Neil's board to design my board using Eagle.

Download the design files for the PCB here:
Schematic
Board
Traces for milling
Outline for cutting

The circuit is a 'Wheatstone brige' with 3 fixed value resistors and 1 variable resistor, which is the thermistor. When the 4 resistors are balanced, there is no current flow. A temperature change will change the resistance of the thermistor and initiate current flow.

The schematic of the circuit in Eagle.

The design of the board in Eagle.

Milling and cutting the board in Modela MDX-20 milling machine.

The components to be soldered on the board.

The board after soldering.

Holding the multimeter pins across the Vcc and GND pins of the chip displays a value of around 5V.

3. PCB programming

Setting up Python3 and installing the required modules in the right place in my Mac was a bit of a job. But felt good when it was done.
Download the programme files here:
Makefile
C file
hex file to be flashed into the ATtiny45
Python3 file to visualize the sensor output on PC (GUI)
Python3 file to visualize the sensor output on PC (IF-ELSE)

1. Using the ISP programmer I made in week 5 (electronics production) to flash the .C programme into the Attiny45.

2. For AVR microcontrollers, the avr-gcc to compile the C code and the avrdude to send the program to the chip are contained in the Makefile.

3. I had to rename the makefile to 'Makefile' without the .make extension. Even after renaming, the .make extension kept showing up in the title bar of Xcode along with the file name and the make command would not work. This was resolved by renaming the file from the Terminal using 'mv Makefile.make Makefile'.

4. With the 'make' command the first four lines of the Makefile are executed which are : name of the file to compile, extension of the file to compile, microcontroller to program and the frequency of the board to program.

5. make program-usbtiny failed in the first attempt due to wrong orientation of the multi-pin connecting the ISP programmer and board.

6. With the right connections, make program-usbtiny command executes the avrdude command to send the .hex program to the chip.

7. Use the FTDI 5V serial cable to connect the board to the PC through USB.

8. Error because pyserial module is not installed.

9. Installing pyserial module using pip command.

10. I had to add parantheses to the statement after print command to adapt the code from Python2 to Python3.

11. I had to install Tkinter, which is a GUI package.

12. Installing tcl and tk packages, followed by testing tkinter import.

13. I had to install Numpy, which is a Python library support for large, multi-dimensional arrays and matrices, along with mathematical functions to operate on these arrays.

14. python3 -m serial.tools.list_ports listed the available two ports.

15.Error when the port ID is not passed in as an argument to the code.

16. Passing in the port ID as argument into the code with the python3 command, followed by filename.

17. The list of thermistors and the B value. I used NHQ103B375T10 and its B value is 3750, which is used in the code to calculate the temperature based on the resistance value.

18.The equation relating B (beta) value with temperature and resistance. Rt1 and Rt2 are resistance values at temperatures T1 and T2 respectively.

19. Exploring the code and editing the size of the box.

20. The tkinter GUI displaying the temperature value. The video at the top shows the sensor in action.

21. Changing the colours in the GUI.

22. The edited GUI.

23. Editing the code with an 'IF-ELSE' statement to display different messages above or below 24 degree C.

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Week 11 - Input devices

1. Group assignment: measure the analog levels and digital signals in an input device

2. PCB production

3. PCB programming

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