Week 4

 Making a buzzer sound

• Discuss max current draws on the Raspberry Pi.
• V = IR
  For GPIO pins this means 
  3.3 = 0.016 R
  R= 3.3/0.016
  R= 206.25 Ohms
  Therefore the lowest resistance we can have in a output circuit is 206.25 Ohms
• How to use the debugger to examine buzzer code.
• Using the "time" calls and turning the output pin on and off make the buzzer sound
• The buzzer sound is too low just using the GPIO pin so we need one of two things
• A transistor to amplify the signal from the GPIO pin without increasing the current draw on the GPIO pin
• A passive buzzer board that has a power and signal input.
• Extension activity making the buzzer sound using PWM
• What are the limits of changing the frequency.  Possible reasons why.

Programming today

• Finish of variables from last week.
• Looping For, While
• Add up numbers 1-100 Using for loop
• Functions (intro) 
• Scope of blocks (counter inside function) use of the global keyword.

Homework

• Using a while loop add Fibonacci numbers and output their values until the Fibonacci number is greater that 100,000
• Extension homework.  Find the largest prime number you can in 1 hr. 
  RSA prime numbers used are between 1024 bits long and 2048 bits long which means they are between.... 2^1024 -1  and 2^2048 -1 
  which for a 1024 bit number the largest number would be (approx)
  179 800,000,(300 zeros) or 1.798 E 308
•  Hints 
• use the % (called the modulo) operator it gives you the remainder after division.
• there is only a need to check numbers up to half plus 1 not all the numbers up to the number.
• To test if one number equals another you have to use the equals operator which is two equals signs in a row.
  eg
   if (4 == 4):
      print(True)
•    
• if you get frustrated google has the answer.  Try to get frustrated first. 

• How to run something for an hour|
  from datetime import date, datetime, timedelta
  from time import sleep
  start_time = datetime.now()
  end_time = start_time + timedelta(hours=1)
  while datetime.now() < end_time:
      print(datetime.now())
      sleep(1)