Intro to Electronics in Python

Intro to Electronics in Python

Anna Gerber Intro to Electronics in Python

Electricity

•  Electricity is a form of energy •  We can connect components that convert

electrical energy into other forms of energy: light, sound, movement, heat etc, into a circuit

•  In a Direct Current (DC) circuit,electrical energy flows from the positive side of a power source to thenegative side, i.e. from + (power) to – (ground)


Electrical concepts

•  Current (Amps): measures the flow of electrical energy through a circuit

•  Voltage (Volts): measures difference in potential energy between the positive and negative sides of a circuit

•  Resistance (Ohms): measures a material's opposition to the flow of energy

•  Power (Watts): the rate at which energy is converted from one form to another


Ohm's Law

Current = Voltage / Resistance

•  Increase the voltage, and the current will increase (i.e. speed up)

•  Increase the resistance and the current will decrease


Sensors

•  Environmental condi/ons (e.g. temperature, humidity, smoke)

•  Magne/c (e.g. hall effect sensor)

•  Light (e.g. photo resistor) •  Sound (e.g. microphone)

•  Mo/on (e.g. accelerometer, /lt, pressure)

•  User / Physical Input (e.g. buDon)


Actuators

•  Light & Displays (e.g. LED, LCD) •  Sound (e.g. Piezo buzzer) •  Mo/on (e.g. Servo, DC Motor, Solenoid)

•  Power (e.g. Relay)


Digital vs Analog

•  Digital –  discrete values (0 or 1)(LOW or HIGH) –  Examples: tilt sensor, push button, relay, servo

•  Analog –  continuous values –  Examples: photo resistor, DC motor

•  Some sensors support both digital and analog outputs


Using a Breadboard


•  Use to prototype circuits without soldering by plugging in components and jumper wires

•  Letters and numbers for reference •  Numbered rows are connected •  Some have power bus along the sides

Resistors

•  Introduces resistance, so restricts the amount of current that can flow through a circuit

•  Coloured bands indicate resistance •  Can be connected in either direction


LEDs

•  Light Emitting Diode •  Polarized: diodes act like one way valves so

must be connected in a certain direction •  Emits light when a current passes through


Anode (+) longer lead connects to power

Cathode (-‐) connects to ground

Control

•  Arduino-compatible Microcontroller co-ordinates robot inputs (sensors) and outputs (actuators)

•  See http://arduino.cc/


PyFirmata

•  https://github.com/tino/pyFirmata

•  Communicates with the Arduino using the Firmata protocol

Install using pip: pip install pyfirmata


Loading Firmata onto the Arduino

•  Once-off setup to prepare our Arduino for use with PyFirmata: –  Connect the microcontroller board via USB –  Launch Arduino IDE and open the Firmata sketch

via the menu: File > Examples > Firmata > StandardFirmata

–  Select your board type (e.g. Arduino Nano w/ ATmega328) via Tools > Board

–  Select the port for your board via Tools > Serial Port > (the port of your Arduino) e.g. /dev/tty.usbserial-A9GF3L9D

–  Upload the program by clicking on Upload –  Close the IDE


BLINKING AN LED


Connecting an LED to the Arduino

•  Unplug the Arduino! •  Attach long lead of

LED to pin 13 of Arduino

•  Connect resistor to cathode of resistor and ground rail of breadboard

•  Connect GND pin of Arduino to ground rail of breadboard using a jumper wire


Creating the program

1.  Create a Python program file (e.g. blink.py) 2.  Edit it using a text editor e.g. SublimeText 3.  At the start of your program import the library

import pyfirmata


Creating the board

We create a Board object which corresponds to our Arduino-compatible microcontroller board and store it in a variable. We need to provide the port as a parameter:

board = pyfirmata.Arduino("/dev/tty.usbserial-‐A9QPTF37")


Controlling the LED

•  Then we can control the LED via the pin it is connected to (in this case, pin 13)

•  Use a variable for the pin number to make it easier to change later –  PIN = 13

•  Turn on LED on pin 13 –  board.digital[PIN].write(1)

•  Turn off LED on pin 13 –  board.digital[PIN].write(0)


Delayed behaviour

•  Use the pass_time function to delay functions by a certain number of seconds e.g. blink LED on then off after one second:

board.digital[PIN].write(0) board.pass_time(1) board.digital[PIN].write(1)


Repeating behaviour (loops)

Use a while loop to blink indefinitely:

while True : board.digital[PIN].write(0) board.pass_time(1) board.digital[PIN].write(1) board.pass_time(1)


The entire blink program

import pyfirmata

PORT = "/dev/tty.usbserial-‐A9QPTF37" PIN = 13 board = pyfirmata.Arduino(PORT)

while True: board.digital[PIN].write(0) board.pass_time(1) board.digital[PIN].write(1) board.pass_time(1)


Running the program from Terminal

•  Open the Terminal app •  Change directory to the location where you have

saved your code e.g.

> cd ~/Desktop/code/

•  Run your program using Python e.g.

> python blink.py

•  Hit control-C to stop the program


Connecting to iPython Notebook

•  We will use iPython Notebook running on Raspberry Pi

•  Plug into Raspberry Pi via ethernet (connect to DHCP server on Pi)

•  Open 192.168.1.1:8888 in your browser


How to setup the software at home

•  Install Arduino IDE –  Optional, only required if you want to load

Firmata again or experiment with programming the Arduino using C++

•  Install Python •  Install PyFirmata •  Install a code editor e.g. Atom (Mac only),

SublimeText if you don't already have one or install iPython Notebook


Where to find out more

•  Electricity –  https://www.khanacademy.org/science/physics/

electricity-and-magnetism/v/circuits--part-1 •  Arduino Playground –  http://playground.arduino.cc/interfacing/python

•  Sample code for Freetronics kit –  https://gist.github.com/AnnaGerber/

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Intro to Electronics in Python

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