Explain the introduction to ADC, ADC characteristics, Programming ADC using PIC18, Introduction to DAC and DAC interfacing with PIC18.

 Discuss the ADC of the PIC18  Explain the process of data acquisition using ADC  Program the PIC18’s ADC in assembly  Describe the basic operation of DAC  Interface a DAC chip to the PIC18

 Digital Computer: Binary (discrete) values  Physical World: Analog (continuous) values  Example: Temperature, Humidity, Pressure  Output: Voltage or Current  Microcontroller? -----> Digital  Therefore, ADC is needed to translate (convert) the analog signals to digital numbers

Microcontroller Connection to Sensor via ADC

n-bitNo. of stepsStep size (mV) 82 8 = 2565/256 = = 10245/1024 = = 40965/4096 = 1.2 Assuming V REF = 5V * Step Size (Resolution): is the smallest change that can be discerned by an ADC

 V ref : Input voltage used for the reference voltage  The voltage connected to this pin, with the resolution of the ADC chip, dictate the step size  Example: If we need the analog input to be 0 to 4 volts, V ref is connected to 4 volts  Digital data output: 8-bit (D0-D7), 10-bit (D0- D9)

V ref (V)V in (V)Step size (mV) to 55/1024 = to /1024 = to 33/1024 = to /1024 = to /1024 = 2 V ref Relation to Vin Range for an 10-bit ADC

D out = V in / Step Size Digital data output (in decimal): 8-bit (D0-D7)= bit (D0-D9) = 1024 Analog Input Voltage Example: V ref = 2.56, V in = 1.7V. Calculate the Do-D9 output? Solution: Step Size = 2.56/1024 = 2.5mV Dout = 1.7/2.5mV = 680 (Decimal) D0-D9 =

 It has 11 analog input channels (AN0 – AN10)  10-bit ADC  Converted values are stored in ADRESH:ADRESL registers

 A/D Control Register 0 (ADCON0)  Controls the operation of the A/D module  A/D Control Register 1 (ADCON1)  Configures the functions of the port pins  A/D Control Register 2 (ADCON2)  Configures the A/D clock source, programmed acquisition time and justification

Different from the Book! Example: ADCON0 =

* Different from the Book!

Example: ADCON1 = * Different from the Book!

Example: ADCON2 =

ADFM Bit and ADRESx Registers

For a PIC18-based system, we have V ref = V dd = 5V. Find a) The step size and b) The ADCON1 value if we need 3 channels. a)The step size = 5/1024 = 4,8mV b)ADCON1 =

 Define in term of Tad (Conversion time per bit)  To calculate: F OSC /2, F OSC /4, F OSC /8, F OSC /16, F OSC /32 or F OSC /64

 TURN ON the ADC module (BSF ADCON0, ADON)  Make the ADC channel pin as input pin  Select voltage reference and ADC channel  Select the conversion speed  Wait for the required acquisition time  Activate the start conversion bit of GO/DONE  Wait for the conversion to be completed by pooling the end-of-conversion GO/DONE bit  After the GO/DONE bit has gone LOW, read the ADRESL and ADRESH register

ORG0000H CLRFTRISC CLRF TRISD BSFTRISA, 0 MOVLW0x00 MOVWFADCON0 MOVLW0x0E MOVWFADCON1 MOVLW0xBE MOVWFADCON2 OV ERCALLDELAY BSFADCON0, GO BACKBTFSADCON0, GONE BRABACK MOVFFADRESL, PORTC MOVFFADRESH, PORTD CALLQSEC_DELAY BRAOVER END

InterruptFlag BitRegisterEnable BitRegister ADIF (ADC)ADIFPIR1ADIEPIE1 ADC Interrupt Flag Bits and Associated Registers * Please see Program 13-2 page 514

 Covert digital pulses to analog pulses  DAC0808 chip: Use R/2R method, 8-bit DAC Block Diagram

 The digital inputs are converted to current (I out )  Connecting a resistor to the I out pin, we convert the result to voltage I out = I ref (D7/2 + D6/4 + D5/8 + D4/16 + D3/32 + D2/64 + D1/128 + D0/256) I ref = Generally set to 2.0mA This will course inaccuracy because the Resistance will affect the reading

Example: Binary input: I out = 2mA (153/256) = 1.195mA and V out = 1.195mA x 5K = 5.975V

Gas Sensor Temperature Sensor Humidity Sensor Sonar Sensor

Characteristic: 1)Precision integrated-circuit 2)Output voltage is linearly proportional to the Celcius 3)Requires no external calibration (Internally calibration) 4)Output: 10mV for each degree

10mV = 1 degree (Minimum) 20mV = 2 degree 30mV = 3 degree. 1000mV = 100 degree (Maximum) Vr ef = ??? 5V Step Size = 4.8mV Step Size = 1mV Vin (max) = 5V Vin (max) = 1.024V Which one suitable? How to set V ref ??

To overcome any fluctuations in power supply. * Please see Program 13-4 page 524

“Things are only impossible until they're not”