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ELCT706 MicroLabSession #3
7-segment LEDs and Analog to Digital Conversion
ELCT 708 Session #3 Dr. Mohamed Abdel GhanyEng. Salma Hesham
7-Segment LED Display
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
g f com a b
e d com c P
7-Segment LED Display
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
Common Cathode - Com Pin = Gnd- Active high inputs- Example inputs to write 3:
pins = a b c d e f g P3 = 1 1 1 1 0 0 1 0
Common Anode - Com Pin = VCC- Active low inputs- Example inputs to write 3:
pins = a b c d e f g P3 = 0 0 0 0 1 1 0 1
Common Cathode 7-Segment input values
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
7-Segment LED Display
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
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.
Analog to Digital Converter
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
Analog voltage values binary numbers (digital values)- Larger number of bits= higher resolution/ more accuracy
Example: Input voltage range from 0 to 5VAvailable bits = 5 bits 23=8 different valuesResolution = full range/#values = 5/32 = 0.625V
Analog input voltage Digital values
0 – 0.625 V 000
0.625 – 1.25 V 001
1.25 – 1.875 V 010
1.875 – 2.5 V 011
2.5 – 3.125 V 100
3.125 – 3.75 V 101
3.75 – 4.375 V 110
4.375 – 5 V 111
Digital value = Analog value × #values/full range
Analog value = Digital value × full range/#values
ADC in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
- PIC16F877A: 10-bit ADC 210 =1024: from 0 to 1023
- PIC16F877A has 4 Specific Function 8-bit Registers for ADC module: 1. ADRESH 2. ADRESL 3. ADCON04. 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
ADC in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
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
ADC in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
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 Bit 7=1 Right justified result
ADRESH ADRESL
10-bit result
ADRESH ADRESL
10-bit result
ADC in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
ADCON1:
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
Analog to Digital Converter
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
ADC in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
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/2 1.25 MHz
01 Fosc/8 5 MHz
10 Fosc/32 20 MHz
11 FRC internal Typ. 4us
ADC in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
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
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
Bit 5,4,3: CHS2, CHS1, CHS0: analog input channel selects
ADC in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
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 statusbit 2 = 1 Conversion in progressbit 2 = 0 Conversion done
Bit 1: not used typically ‘0’
Bit 0: ADON: Activate ADC modulebit 0 = 1 ADC activatedbit 0 = 0 ADC OFF
Steps for A to D Conversion in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
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.
Show temperature on 7-segment display using LM35 and ADC in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
Task 2Write 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 Vin to the analog channel AN0/RA0
- The output of the sensor is linearly dependent on the temperature such that each 1 degree Celsius = 10mV.
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
Calculate the equivalent voltage from the DAC output : Veq = 51 × (5V/1024)= 249mV
calculate the temperature from the ADC output: 249mV/10mV=24.9Send each digit of temperature to one 7 segment display
Steps for A to D Conversion in PIC16F877A
ELCT 708 Session #3Dr. Mohamed Abdel GhanyEng. Salma Hesham
LM35 sensor
