Software - Initial Test

INTRO

Our first program verifies the basic functions of the voltmeter using a manual setting of voltage range. This limited test helps us focus on the ADC reading and display only. The Pushbutton for Range Select will be implemented in the next test.

NOTE: Even though we have NO analog prototype built yet, we can still write code and run a basic PRE-TEST with the Arduino UNO Board by itself.

Check out the Software Design overview.

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ARDUINO BASICS

Here's the fast track version of running a C program (sketch) on your Arduino Board.

• Open the Arduino IDE Software
    https://www.arduino.cc/en/software
• Connect UNO Board to your computer
    https://docs.arduino.cc/hardware/uno-rev3/
• Select Board Name
    Select UNO from drop down menu.
• Open or write a program (sketch)
    DVM1_initial_test1.ino
• Click Compile Button
    Generates executable code, checks for errors.
• Click the Upload Button
    Upoads compiled code into UNO and begins running.
• Click the Serial Monitor
     Window displays output from PrintSerial statement.

 

ARDUINO + ANALOG SCHEMATIC

The schematic shows the physical world that the code can control to implement our meter.

 

FLOW CHART

Here's a shortened Flow Chart that skips the Pushbutton reading so we can focus on the ADC Read and Display.

 

CODE STRATEGY / THEORY

A quick refresh of the ADC equation shows Vinput given the digital code ADCword.
  

You just need to set Kdiv depending on the present Voltage Range 

• If Vrange = 0 (4V),   then Kdiv = 1
• If Vrange = 1 (20V), then Kdiv = R2/(R1+R2)

Similarly, set the divider switches according to the Voltage Range

• If Vrange = 0 (4V),   then SW1=ON,  SW2=OFF (direct connect)
• If Vrange = 1 (20V), then SW1=OFF, SW2=ON  (connect to divider tap)

Arduino Pin usage.

• A0 Analog Input - Voltage Reading
• D12 Digital Output - SW1 R Divider
• D13 Digital Output - SW2 R Divider
• D8 Digital Input - Pushbutton for Vrange

 

THE CODE

Caution Ahead - hardware person writing code! Granted, the program is so straighforward it's easy to create some reasonable code. However, I'm open to any suggestions from those with more Software experience.

Declarations

The variable declararions occur before the setup() function.

 

Setup()

This code excecutes once in the Arduino Sketch. Note how the Vrange is set and then the digital bits D12,13 are set for resistor divider switches SW1,2. See comments in gray for code description.

 

Loop()

This code runs continuously. The main voltmeter tasks happen here. To write this function, simply follow the flow chart and write the C code for each block. See comments in gray for program description.

 

PRE-TEST

What can we test even though the analog circuitry has NOT been prototyped? Good news! We can jumper the Arduino's 3.3V supply directly into the A0 analog input.

• Insert jumper wire from 3.3V Socket to the A0 Socket.
• Open program (sketch)
    DVM1_initial_test1.ino
• Edit statement in setup():
    Vrange=0 (4V range)
• Click the Upload Button
    Also Compiles before uploading.
• Click the Serial Monitor
• Does the reading show about 3.3V?
    if Yes, then celebrate the success!
    if NO, then check code and jumper.
   
• Edit statement in setup():
    Vrange=1 (20V range)
• Click the Upload Button
• Click the Serial Monitor
• Does the reading show about 3.3V x 5 = 16.5V?
    if Yes, then celebrate the success!
    if NO, then check code and jumper.

 

NEXT UP

Having built and tested our initial working code, let's take the next step in creating software for a Basic Voltmeter by adding a pushbutton for Vrange change.

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