INPUT DEVICES

Assignment

• Measure something: add a sensor to a microcontroller board that you have designed and read it.
• Measure the analog levels and digital signals in an input device.

What I Did

• Designed a board with a Phototransistor in Eagle
• Milled and soldered the components
• Programmed the board

Input devices available in fablab are PIR, ultrasonic, hall effect sensor, temperature sensor, light sensor and accelerometer. I decided to try light sensor which is a photo transistor for this week's assignment.

Introduction

A phototransistor is a light-sensitive transistor. A common type of phototransistor, called a photobipolar transistor, is in essence a bipolar transistor encased in a transparent case so that light can reach the base–collector junction.

I made a board in which an LED is activated by the phototransistor. The values are set in the programming for the LED to activate and deactivate. The design was made using Eagle. Below is the schematic of the circuit

The image was exported as image file in monochrome.

Final board

The components were soldered correctly

The FTDI cable had to be connected at the edge, but there was a connection that had a chance to get shortcircuited near the edge. So I put a masking tape over it before soldering the FTDI pins.

The Final Board

Programming the Board

ATtiny45

I used ATtiny45 for this board. The pinout diagram is as below

I used Arduino to program the board. The pins were set and the programming was was done as follows

            #include<SoftwareSerial.h>
            SoftwareSerial window(0,1);// rx tx 
            void setup(){
              window.begin(9600);
              pinMode (PB4,OUTPUT);
            
            }
             void loop()
             {
              int light= analogRead(A3);
            
              window.println(light);
            
              if(light <=400)
            
              {
                digitalWrite(PB4,LOW);
                
              }
            else
            {
              digitalWrite(PB4, HIGH);
            }
            }
            
            
            
            

Final Output

The programming was successful. The phototransistor was working perfectly. The output values were showing on the laptop screen. It was programmed to light up the LED for all values above 400 and the LED remains off for all values below 400.

Download files here