Week 12: Input Devices
20th April - 26th April 2022
Task to be carried out this week
Group Assignment
  1. probe an input device's analog levels and digital signals
    2. Link to Group Assignment
Individual Assignment
  1. measure something: add a sensor to a microcontroller board that you have designed and read it
The softwares used during the week's assignment
  • Autodesk Eagle: Microcontroller Board Design
  • MIT Mods: To create toolpath for Roland SRM-20 Milling Machine
  • Arduino IDE: Porgramming the board
  • Visual Studio: For Documentation
Action Plan
Date Work Allocation
20th April Lecture on Input Devices by Prof. Neil
21st April Lecture on Input Device by Local Instructor and selection of Input device to use for the week
22nd April Board Design
23rd April Milling and Soldering the board
24th April Board Testing and Porgramming
25th April Board Testing and Programming
26th April Documentation
Input Devices and Introduction to LM35

What are Input Devices?

An input device is any hardware component that collects data from its surrounding and sends it to the microcontroller it is connected to.
Some examples of input devices are;

LM35-Temperature Sensor
The main task for this week's assignment was to add an input device to my microcontroller board and then use it to measure something. I choose the LM35 temperature sensor which is used for measuring the temperature of its surrounding. I choose it because for my final project as well, I need to connect a temperature sensor to get the data for my kiln temperature. Before using LM35 temperature sensor, I needed to understand what it was and how it functioned.

LM35 is a low cost temperature sensor that outputs an analog signal which is proportional to the instantaneous temperature. It gives the temperature readings in degree celsius and doesn't require any external caliberation. It has 3 pins out of which one is a data pin, one a power pin and one the ground pin.

Feature of LM35

  • Calibrated Directly in Celsius (Centigrade)
  • Linear + 10-mV/°C Scale Factor
  • 0.5°C Ensured Accuracy (at 25°C)
  • Rated for Full −55°C to 150°C Range
  • Operates from 4 V to 30 V
  • Less than 60-µA Current Drain
  • Low Self-Heating, 0.08°C in Still Air
  • Non-Linearity Only ±¼°C Typical
  • Low-Impedance Output, 0.1 Ω for 1-mA Load
More information on LM35 can be found here

Board Design and soldering

I had to design one more board for this week's assignment. Initially, during my output week, I designed a board that kept provision for adding an input device but the board didn't work. So for the finalboard of the output week, I forgot to keep provision for input device. hence, I had to design another board for this week. I used the ATTiny44 microcontroller for this week. Because I faced alot of issues when using the ATTiny44 Microcontroller during my output week, I cross checked on internet as well as got suggestion form the local instructor before my board design. After I confirmed that ATTiny44 was compatable to be used with LM35, I started my board design. I kept the design of the board simple. I added the following components to my board;

  • ATTiny 44: The microcontroller for the board
  • 3-pin female header: to connect my LM35
  • 6-pin header: To connect the FTDI connector (I needed this for serial reading)
  • 2*3-pin header: For AVRISPSMD connector
  • Two LEDs: One for power and one for test
  • 20Mhz Resonator
  • one reset switch
  • One Micro-ferret Capacitor
  • Three resistors: Two 499ohm resistor for the 2 LEDS and one 10 Kilo-ohm resistors for switch

I connected pin 11 of my ATTiny 44 to the data pin of the LM35. Once the design was completed, I milled my board and soldered all the components on it.

Testing and Programming the board

After the board was completed, I started with the programming. I used the USBTiny/FabISP as a programmer to program my board and also connected the board to FTDI connector.

Before compiling the program LM35, I tested my board by uploading a simple blink program. Once that worked, I tried a simple temperature display program. In the program, I had to define the LM35 datapin and the RX and TX pin numbers. I also had to add the SoftwareSerial.h library.

Output:

Next I tried another program, whereby the temperature read by the LM35 controlled the test LED on the board. To do that, I defined a constant temperature and programmed the board to turn off the LED if the temperature read was below the defined constant and to turn the LED on of the temperature read was greater than the defined constant. The program successfully compiled and the board functioned as programmed.

Result: INPUT DEVICES
Project Files