Description
LAB 5: A/D converter, Temperature Sensor & Light Sensor
Build the circuit shown on the attached schematics. You will need to get the following datasheet for the device at the location marked ‘U2’:
http://www.ti.com/lit/ds/symlink/lmt84.pdf
Make sure that you pay attention on the datasheets page 4 with the package TO-92 about how to determine the pins of this device especially that the pictures shown on the document do indicate that the views are for TOP VIEW. Failure to properly connect the pins could result into damaging the parts especially the LMT84! The view on the schematics shows the same TOP view of the parts.
The goal of this lab is to write a program that will perform the following steps:
1) 2) 3) 4)
5)
6)
Read the voltage from the LMT84 using the PIC18F4620’s ADC Channel 0
Calculate the temperature in degree C.
Convert that voltage into the equivalent temperature (in degree F).
Display the temperature in degree F onto to two 7-segment displays. See the schematics to get the connections of each of the 7-segment display.
Output the same result to the TeraTerm terminal so that we can see the data on a computer screen. Display on the screen the voltage readout of the LMT84 and the temperatures in degree F.
In addition, the circuit does include two common cathode RGB LEDs called D1 and D2. Get the program to do the following:
a) D1 will show the range of the temperature as follows:
Temperature Range Below 10 F
10-19 F 20-29 F 30-39 F 40-49 F 50-59 F 60-69 F Above 70 F
D1’s color Off
Red Green Y ellow Blue Purple Cyan White
Write the ‘c’ code in the most efficient way for this exercise! Even though you can use ‘if statement’ or ‘case statement’ to check the conditions, find a more direct to control the LED.
b) The RGB LED D2 will show different colors based on the following conditions:
Temperature Range Below 45F
46F – 55F
56F – 65F 66F – 75F Above 76F
D2’s color Off
Red Green Blue White
7) Measure the voltage at the pin AN1 coming from the photo resistor PR1. Change the color of the Common-Cathode D3 based on the following voltage reading:
AN1 voltage
< 2.5V
>=2.5V && < 3.4V >= 3.4V
Guidance/Help:
1) ADCON0 and ADCON1
D3’s color RED GREEN YELLOW
To convert the voltage into digital readings, you will need to learn how to use the Analog/Digital Converter:
First, you need to initialize the A/D Converter. Chapter 19 of the PIC18F4620 Datasheets (http://ww1.microchip.com/downloads/en/devicedoc/39626e.pdf) talks about this piece of hardware. You need to pay attention to the two registers ADCON0 and ADCON1.
The first register (ADCON0) is to select which pin to use in the A/D conversion (See pdf page 225 of the datasheets). The output from the temperature sensor LMT84 is connected to AN0 or RA0. You need to set the proper value for ADCON0 in order to use AN0. In addition, you need to force bit 0 to ‘1’ and bit 1 to ‘0’.
The second register ADCON1 (see pdf page 226) is to specify what pins to be used as analog (for A/D purpose) versus digital. Read the definitions of the ADCON1. The lower 4 bits specify which pins are to be used as analog or digital. In our application here, AN0 through AN3 are to be analog. Choose the minimum configuration to force those pins to be analog while the remaining pins must be set as digital.
Next, bits 4 and 5 specify the source of the two reference voltage pins. Use the settings that pick VREF+ instead of VDD for bit 4 and VSS for bit 5.
Follow the descriptions on the comment lines below to determine what value you should use for each register
void Init_ADC(void) {
}
}
ADCON0=0x??; ADCON1=0x??;
ADCON2=0xA9;
// select channel AN0, and turn on the ADC subsystem
// select pins AN0 through AN3 as analog signal, VDD-VSS as // reference voltage
// right justify the result. Set the bit conversion time (TAD) and // acquisition time
2) Measuring the Analog Voltage
You will need to use the following routine to get the result (this routine was in your tutorial):
unsigned int get_full_ADC(void) {
int result
ADCON0bits.GO=1; while(ADCON0bits.DONE==1);
result = (ADRESH * 0x100) + ADRESL; return result;
// Start Conversion
// wait for conversion to be completed // combine result of upper byte and
// lower byte into result
// return the result.
3) Temperature Conversion
Read the spec of the LMT84 to determine how to convert the voltage reading into equivalent temperature.
4) Display Temperature into 7-segment displays
The provided dual-digit 7-segment has the following datasheet:
https://www.datasheet.live/index.php?title=Special:PdfViewer&url=https%3A%2F%2Fpdf.datas heet.live%2F31e73430%2Fledtech.com%2FLA5622-11.pdf
Once you get the digital readings of the temperature in degree C, you will need to convert it into degrees F.
Next, you will have to break that temperature into two numbers, one for the upper digit and the other one for the lower digit. For example, a value of 81F will have the upper value of 8 and the lower value of 1.
After the two BCD digits are obtained, you need to convert each digit from a decimal value into a value that decodes that BCD digit into 7-segment display. Create a bitmap for each digit as follows: (Remember that the 7-segment is a common anode and therefore logic 0 with turn on the segment while a logic 1 will turn it off).
UPPER BCD Digit
0 1 2 3 4 5 6 7 8 9
PORT
7 6 5 4 3 2 1 0 HEX number
gfe dcb a
x1000000 0x40 x1111001 0x79
Refer to the following link to see all the combinations of the BCD digits (scroll down to ‘Displaying letters’):
https://en.wikipedia.org/wiki/Seven-segment_display
Once all the values are obtained, gather them and place them into an array to be used to output to the corresponding port supporting the 7-segment display.
Use the digit of the number to be displayed as the offset to the array in order to obtain the bit pattern for that digit. Once that value is obtained output it to the Port associated with the 7- segment display. Since the 7 segments of the upper digit are in PORTC, then you can output the value of the array directly to that port. The lower digit on the other hand only has 6 segments on PORTC while the segment ‘g’ sits on bit 0 of PORTE. You should use a mask operation to output the lower 6 bits to PORTC and test bit 6 to decide to output a ‘0’ or a ‘1’ on bit 0 of PORTE..
5) Display on the TeraTerm
To debug and troubleshoot your software, you will have to use the serial port and the TeraTerm software to print message on the screen. In order to get the serial port to work, you will need to have the following sections added into your code.
First, you have to make sure that the following lines appear at the beginning of the program:
#include <p18f4620.h> #include <stdio.h> #include <math.h> #include <usart.h>
#pragma config OSC = INTIO67
#pragma config WDT=OFF #pragma config LVP=OFF #pragma config BOREN =OFF
Second, you do need to add this routine at the start of the program (preferably before the main() routine):
void init_UART() {
OpenUSART (USART_TX_INT_OFF & USART_RX_INT_OFF & USART_ASYNCH_MODE & USART_EIGHT_BIT & USART_CONT_RX & USART_BRGH_HIGH, 25);
OSCCON = 0x60;
}
Next, at the start of the main() routine, you have to add to call the init_UART() routine above.
To print something out on the serial port, you have to use the ‘printf’ statement. You can ‘google’ for the proper use of this printf statement. For example, to print the content of a variable ‘x’ with a heading in from of the data, you can have something like:
printf (“ x = %d \r\n”,x);
Notice the use of %d and the control function ‘\r’ and \n’. You need to revisit those control functions in the ‘printf’ statement to know how to use them.
Here are the lines that you should have all together:
#include <p18f4620.h>
#include <stdio.h>
#include <math.h>
#include <usart.h>
#pragma config OSC = INTIO67 #pragma config WDT=OFF #pragma config LVP=OFF #pragma config BOREN =OFF
void putch (char c) {
while (!TRMT);
TXREG = c; }
void init_UART() {
OpenUSART (USART_TX_INT_OFF & USART_RX_INT_OFF & USART_ASYNCH_MODE & USART_EIGHT_BIT & USART_CONT_RX & USART_BRGH_HIGH, 25);
OSCCON = 0x60;
}
void main() {
init_IO(); init_UART();
// Place the rest of your code here }
Note: Remember to set the ‘Link in Peripheral Library’ as you have done in LAB1 Part 2. Here are the steps from that lab:
- Select the project and right click on it. Scroll all the way down to Properties and click on it.
- A new screen will appear. Select ‘XC8 linker’ and then go the right side and scroll until you see the selection. Check on that option. Hit OK afterwards.
6) Set different colors for the RGB LED
One convenient way to set an individual output is to use the ‘#define’ statement. For example, we can have the following:
#define D1_RED #define D1_GREEN #define D1_BLUE
PORTBbits.RB0 PORTBbits.RB1 PORTBbits.RB2
Once you have defined those variables, you can force a color upon the RGB LED by applying the proper logic to each variable to get the desired color. For example, to set the RED color for a common-cathode RGB LED, you can write this routine:
void SET_D1_RED() {
}
D1_RED = 1; D1_GREEN = 0; D1_BLUE = 0;
The same for setting the yellow color:
void SET_D1_YELLOW() {
D1_RED = 1; D1_GREEN = 1; D1_BLUE = 0;
}
Do the same for the other colors. Also, repeat the same procedure for the second RGB LED D2.
