ELCT706 MicroLab Session #3 7-segment LEDs and Analog to Digital Conversion. Eng. Salma Hesham

Transcription

1 ELCT706 MicroLab Session #3 7-segment LEDs and Analog to Digital Conversion

2 7-Segment LED Display g f com a b e d com c P

3 7-Segment LED Display Common Cathode - Com Pin = Gnd - Active high inputs - Example inputs to write 3: pins = a b c d e f g P 3 = Common Anode - Com Pin = VCC - Active low inputs - Example inputs to write 3: pins = a b c d e f g P 3 =

4 Common Cathode 7-Segment input values

5 7-Segment LED Display Task 1 Write the MikroC code to control a one digit 7- segment display connected to PORTB of the PIC16F877A such that it counts from 0 to 9 with 1 second delay.

6 Analog to Digital Converter Analog voltage values binary numbers (digital values) - Larger number of bits= higher resolution/ more accuracy Example: Input voltage range from 0 to 5V Available bits = 5 bits 2 3 =8 different values Resolution = full range/#values = 5/32 = 0.625V Analog input voltage Digital values V V V V V V V V 111 Digital value = Analog value #values/full range Analog value = Digital value full range/#values

7 ADC in PIC16F877A - PIC16F877A: 10-bit ADC 2 10 =1024: from 0 to PIC16F877A has 4 Specific Function 8-bit Registers for ADC module: 1. ADRESH 2. ADRESL 3. ADCON0 4. ADCON1 Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADRESH A2D Result Register - High Byte ADRESL A2D Result Register - Low Byte ADCON0 ADCS1 ADCS0 CHS2 CHS1 CHS0 GO/DONE - ADON ADCON1 ADFM PCFG3 PCFG2 PCFG1 PCFG0

8 ADC in PIC16F877A 1. ADRESH & 2. ADRESL Registers - PIC: an 8-bit microcontroller - ADC result = 10 bits ADC result needs 2 registers ADRESH & ADRESL. Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADRESH A2D Result Register - High Byte ADRESL A2D Result Register - Low Byte ADCON0 ADCS1 ADCS0 CHS2 CHS1 CHS0 GO/DONE - ADON ADCON1 ADFM PCFG3 PCFG2 PCFG1 PCFG0

9 ADC in PIC16F877A 3. ADCON0 & 4. ADCON1 Registers: Used to configure the ADC module ADCON1: Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADCON1 ADFM PCFG3 PCFG2 PCFG1 PCFG0 Bit 7: ADFM: Analog to Digital Format of the 10-bit result in ADRESH and ADRESL Bit 7=0 Left justified result ADRESH ADRESL Bit 7=1 Right justified result ADRESH ADRESL 10-bit result 10-bit result

10 ADCON1: ADC in PIC16F877A Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADCON1 ADFM PCFG3 PCFG2 PCFG1 PCFG0 Bits 6,5,4: Not used so typically = 000 Bits 3,2,1,0: PCFG3-0: PORT Configuration of ADC module

11 Analog to Digital Converter

12 ADC in PIC16F877A 3. ADCON0: Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADCON0 ADCS1 ADCS0 CHS2 CHS1 CHS0 GO/DONE - ADON Bit 7&6: ADCS1, ADCS0: clock frequency selects ADCS1 ADCS0 Clock frequency Max freq 00 Fosc/ MHz 01 Fosc/8 5 MHz 10 Fosc/32 20 MHz 11 FRC internal Typ. 4us

13 ADC in PIC16F877A 3. ADCON0: Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADCON0 ADCS1 ADCS0 CHS2 CHS1 CHS0 GO/DONE - ADON Bit 5,4,3: CHS2, CHS1, CHS0: analog input channel selects CHS2 CHS1 CHS0 Analog Input channel 000 Channel 0 AN0/RA0 001 Channel 1 AN1/RA1 010 Channel 2 AN2/RA2 011 Channel 3 AN3/RA3 100 Channel 4 AN4/RA5 101 Channel 5 AN5/RE0 110 Channel 6 AN6/RE1 111 Channel 7 AN7/RE2

14 ADC in PIC16F877A 3. ADCON0: Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 ADCON0 ADCS1 ADCS0 CHS2 CHS1 CHS0 GO/DONE - ADON Bit 2: GO/DONE : Conversion status bit 2 = 1 Conversion in progress bit 2 = 0 Conversion done Bit 1: not used typically 0 Bit 0: ADON: Activate ADC module bit 0 = 1 ADC activated bit 0 = 0 ADC OFF

15 Steps for A to D Conversion in PIC16F877A 1. Configure analog & digital pins and Vref (ADCON1) 2. Select ADC clock frequency (ADCON0) 3. Turn ON ADC module (ADCON0) 4. Select ADC input channel (ADCON0) 5. Wait for Acquisition time ( 20µs) 6. Start conversion (set Go/Done bit = 1 in ADCON0) 7. Wait for conversion to complete(check on Go/Done) 8. Read ADC result from ADRESH and ADRESL Next conversion go back to step 4.

16 Show temperature on 7-segment display using LM35 and ADC in PIC16F877A Task 2 Write the MikroC code to display the room temperature on 2 digit 7- segment displays connected to PORTB and PORTD of the PIC16F877A. - The temperature is read by the sensor LM35 which inputs the analog voltage V in to the analog channel AN0/RA0 - The output of the sensor is linearly dependent on the temperature such that each 1 degree Celsius = 10mV.

17 Steps for A to D Conversion in PIC16F877A Example of inputs and outputs to the circuit If Temperature sensed by LM35 = 25 C, it will output 25 10mV = 250mV to Pin AN0 of PIC16F877A ADC module converts the 250mV to digital value = 250mV (1024/5V)= 51 Read output from ADRESH and ADRESL = 51 LM35 sensor Calculate the equivalent voltage from the DAC output : Veq = 51 (5V/1024)= 249mV calculate the temperature from the ADC output: 249mV/10mV=24.9 Send each digit of temperature to one 7 segment display Dr. Mohamed Abdel Gha