{"id":288,"date":"2018-09-28T16:23:46","date_gmt":"2018-09-28T16:23:46","guid":{"rendered":"http:\/\/blogs.plymouth.ac.uk\/embedded-systems\/?page_id=288"},"modified":"2019-09-12T13:53:22","modified_gmt":"2019-09-12T13:53:22","slug":"topic-3-digital-inputs-and-multiple-outputs","status":"publish","type":"page","link":"https:\/\/blogs.plymouth.ac.uk\/embedded-systems\/microcontrollers\/mbed-os-2\/courses\/embedded-systems-in-context-level-4\/topic-3-digital-inputs-and-multiple-outputs\/","title":{"rendered":"Topic 3 – Digital Inputs and Multiple Outputs"},"content":{"rendered":"

Back to ToC<\/a><\/p>\n

In this section, we will look at digital inputs, and how we might use them to control digital outputs.\u00a0We will be using a simple \u201cpush-to-make switch<\/b><\/a>\u201d to generate a single digital bit of data.<\/p>\n

Intended Learning Outcomes<\/b><\/h1>\n
    \n
  1. Configure an digital input with a push to make switch<\/li>\n
  2. Use a pull up\/down resistor to avoid floating inputs<\/li>\n
  3. Write software to read a switch state<\/li>\n
  4. Use programming methods to avoid switch bounce<\/li>\n
  5. Control multiple digital outputs with binary numbers<\/li>\n
  6. Use binary operators to manipulate binary numbers<\/li>\n<\/ol>\n
    \n

    Activity 3.1 – Simple Switch Input<\/h1>\n
    \"\"
    Push to Make Switch<\/figcaption><\/figure>\n
    \"\"
    Schematic Symbol for a Push-to-Make Switch<\/figcaption><\/figure>\n

    Remember that a single digital signal is either ON or OFF. Numerically, we represent this as 1 or 0 (a single binary digit).\u00a0The simplest way to generate a single bit input signal is with a push switch.\u00a0<\/span><\/p>\n

     <\/p>\n

     <\/p>\n

     <\/p>\n

    The schematic to generate a digital input is as follows.<\/p>\n

    \"\"
    Schematic for a single push switch input<\/figcaption><\/figure>\n

    In addition to the switch, wire up 3 LED\u2019s as shown here.<\/p>\n

    \"\"
    Schematic for the LED outputs<\/figcaption><\/figure>\n

    These will be used for outputs.A suggested prototype board layout is shown below:<\/span><\/p>\n

    \"\"
    Prototype board layout for the three LEDs and Push Switch<\/figcaption><\/figure>\n

    Task 3.1.1<\/h2>\n

    In the first task, we are simply going to observe the digital input with a DVM when the =button is pressed and released.<\/p>\n\n\n\n\n
    Using the digital volt meter, measure the voltage across R4 when the button is pressed, and when it is released\u00a0<\/span><\/td>\n<\/tr>\n
    Tip – this can be tricky, so get someone to press and release the button for you while you hold the DVM leads.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
    \"Setting
    Setting your Digital Volt Meter (DVM) to DC Voltage mode, measure the potential difference between these two points<\/figcaption><\/figure>\n
    \n

    Activity 3.2 – Reading Digital Inputs<\/h1>\n

    For this task, we are going to read the digital input using software. The objective is as follows:<\/p>\n