Welcome to Lab! Feel free to get started until we start talking! The lab document is located on the course website:

Transcription

1 Welcome to Lab! Feel free to get started until we start talking! The lab document is located on the course website: You do not need to keep the same partner from last lab We will come around checking your pre-labs after we introduce the lab Let us know if you have any questions!

2 Lab 3: Time and Temperature Display The Introduction

3 Basic Components You will make your MSP430 board use timers and the ADC do the following: Display the date & time (from some start value) Display the current temperature (C and F) Use the scroll wheel setting to control the buzzer Data acquisition is fun! (And important!)

4 Breaking it down Acquire Data (ADC, time count, etc.) Convert to useful format (Degrees, Hr/Min/Sec, ) You know how to do all of these now you can put them together! Format data as string to display Draw on LCD!

5 How to start (Try these first!) Start with the basic components: 1. Functions to setup the ADC and read data from the temp sensor & scroll wheel 2. A function to convert the time 3. A function to convert a number into an string for drawing Acquire Data (ADC, time count, etc.) Convert to useful format (Degrees, Hr/Min/Sec, ) Format data as string to display Draw on LCD!

6 Configuring the ADC You need to take data from two sources: the temp sensor and the scroll wheel It s up to you how to use the ADC to do this Do you want to use single or multiple channels? Do you want to use interrupts? The choice is yours! There is a complete example for the temp sensor (adc12_tempsensor.c) in the lecture notes!

7 Converting the time You will keep time by storing ONE count of elapsed seconds (UTC time) Increment it every second in your ISR You are responsible for converting it to days, months, hours, etc Try this on paper first, then implement it See the note in the lab document about integer truncation it will save you lots of headaches!

8 Formatting the data: Strings Once you have converted your data, you need to put it in a string to display on the LCD This involves finding the ASCII value for each digit and arranging them in a character array (ie, a string ) You may NOT use sprintf() for this, you must do it yourself. If you use sprintf(), we will not sign you off. Why?

9 Why can t I use sprintf()? sprintf() uses a lot of memory. If you try to use it for anything complex, it WILL overflow the stack: If this happens, it will overwrite variables in your code without warning, tainting your world with madness But I used it in my last lab! You were probably printing one value and got lucky. Don t try it again. You've been warned.

10 Help with strings Today, think about how you would write a function to take in a number (eg, 1234) and turn it into a character array, { 1, 2, 3, 4 } An example of how you d use such a function: char str[10]; // Make an array that can hold 10 chars, // which makestring will fill in makestring(1234, str); void makestring(int input, char *s) { // Your code goes here! // You can access the string str as an array like so: s[0] = A ; // Put character A in 1 st index of str } Think about this and feel free to ask us for help!

11 Help with strings (contd.) In general, remember that strings are arrays of characters They contain ASCII values They have a null terminator at the end (Google it!) You must treat strings as arrays, so You must allocate space for them: char *s; // Pointer (likely NOT what you want) char s[5]; // 5 chars that could hold a string If you want to copy a string, you need to do this one byte at a time use memcpy() or write a function Never return one from a function (Why?) If you have conceptual questions on how

12 Buzzer mode Use the ADC to read a value from the scroll wheel (a potentiometer) Don t forget to figure out the potentiometer circuit first (see HW#4, class notes and board schematic) Once you have an ADC value, your job is to map that value to a buzzer pitch Reuse your tuned buzzer function from Lab 2

13 Debugging This nice, linear flow means that you can easily debug where a problem can occur. You can set breakpoints at each part to see if the data is correct at that point Are you getting an ADC value? Is the conversion correct? Does the string look right? Acquire Data (ADC, time count, etc.) Convert to useful format (Degrees, Hr/Min/Sec, ) Format data as string to display Draw on LCD!

14 Debugging is useful! Thinking about a problem like this can save you time! Pay attention to the following techniques for debugging your lab; keep them in mind as you work This will save you lots of frustration later! This kitty didn t care about debugging and was frustrated... Don t be like this kitty.

15 Debugging: ADC This ADC read a value is it correct? Put a breakpoint after you read from the ADC Either examine your variables, or you can look at the ADC registers directly! Does the value make sense?

16 Debugging: Time conversion This value is wrong! Truncation == BAD! Step through your time conversion and examine your variables for hours, minutes, days, etc. The conversion results should match what you got on paper Watch for truncation issues! (See note in lab assignment!) If you want to test, you can type arbitrary math into the expressions window and see how it gets evaluated

17 Debugging: Strings Null terminator (view it in hex!) Look at your string in the debugger before you draw it, or step through as you build it You can see the value for each character! If something shows up as a., it s probably a non-ascii character. Right click and set the number format to Hex to see its value

18 Good luck and have fun! If you have issues, try using these techniques for debugging, they will save you time! Feel free to ask us if you have questions we re here to help! Take a look at the FAQs Thank you for listening!

19 Frequently Asked Questions My display prints What do I do? Put a breakpoint BEFORE you draw the string and make sure it looks correct Does your string have a null terminator? What s a null terminator? Google is your friend... What does AUTO_STRING_LENGTH in graphicis drawing functions mean? If you replace this value with a number, GrStringDraw will only draw that many characters. AUTO_STRING_LENGTH tells it to draw until it finds a null terminator