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Arduino 1 2 1. 2. (Digital to Analog Conversion) 3. (Analog to Digital conversion) 3 Analog to Digital Converter (ADC) Digital to Analog Converter (DAC) (Digital-to-Analog Converter D/A D2A) 4
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Arduino
1 2
1.
2.
(Digital to Analog Conversion)
3.
(Analog to Digital conversion)
3
Analog to Digital Converter
(ADC)
Digital to Analog Converter
(DAC)
(Digital-to-Analog Converter D/A D2A)
4
DAC
Binary Weighted DAC
- Uses switches & precision resistors
- Difficult to achieve high density due to large resistance values
R/2R Ladder
- Most common method
- Keeps resistance values low
- Uses intricate interconnections
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Binary Weighted DAC
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Op-Amp Review
For Negative Feedback,
1. Inputs impedance = Ri
2. Vout = -ixRF = -(Vin/Ri) xRF
3. Voltage gain is : Av = Vout/Vin = -Rf / Ri
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Vin
i+ -
i+ -
Binary Weighted DAC
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D3- D0 0 Vout = 0
D3 D0 1 Vout = -1k x (i3+i2+i1+i0)
Binary Weighted DAC
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D3- D0
Vout = - Vref x Rf x(1/1k + 1/2k + 1/4k + 1/8k)
Vout = -Vref x 1 x(1/1 + 1/2 + 1/4 + 1/8)
Vout = -Vref x (1 + .5 + .25 + .125)
Vout = -1.875 x Vref
Vref = +5V Vout 1 -9.375
R2R Ladder DAC
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R2R Ladder DAC
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Summing
Amp
Inverting
AmpR2R Ladder Network Stage
Thevenin
Rth Thevenin
Rth
0 Rth = 1 k, 1 Rth = 1 k, 2 Rth = 1 k, 3 Rth = 1 k, 4 Rth = 1 k, 5 Rth = 1 k,
6 Rth = 1 k 7 Rth = 1 k
Summing
Amp
Inverting
Amp
Thevenin equivalent Rth
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Bit 7
1 k
Bit 6
1 k
Bit 5
1 k
Bit 4
1 k
Bit 3
1 k
Bit 2
1 k
Bit 1
1 k
Bit 0
1 k
Thevenin Voltage the R2R Ladder Network (Vth)
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VTH 7
VTH7 = 6V
Thevenin Voltage (Vth6)
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VTH
Thevenin Voltage (Vth6)
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VTH
Thevenin Voltage the R2R Ladder Network (Vth)
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Bit 7
6 V
Bit 6
3 V
Bit 5
1.5 V
Bit 4
0.75 V
Bit 3
0.375 V
Bit 2
0.1875 V
Bit 1
93.75 m V
Bit 0
46.875 m V
VTH
Thevenin
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Analog Outputs
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2
21)(
256 IN
F
TH
FREFLSBOUT
R
R
R
RVV
2
21)(
2 IN
F
TH
FREFMSBOUT
R
R
R
RVV
2
21
8)(2 IN
F
TH
F
n
REFAnyBitOUT
R
R
R
RVV
10
10)()(MSB
InputVV MSBOUTTotalOUT
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10
min 10
10
min 10
Re
Re
Re
Re
OUT
OUT
OUT
OUT
solution
solution
V XOUT
V V Xmin 10min 10OUT
solutionV XOUT
solutionV V Xmin 10min 10OUT
OUT
+
ref
min
max
10
= OutputVoltage
=VoltageReference+
=Minimumoutput voltage
= Maximumoutput voltage
= Input value base10
n =
V
V
V
V
X
DAC 800 Pinout and Application
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This is a current producing DAC, with the output determined by the digital code
and by the input voltage Vref. It is very fast (~100 ns), as with most DACs
DAC 800 Diagram
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The current output makes it faster (no op amp to limit). It still has the R-2R
ladder. To analyze this imagine this connection diagram. We will first focus on
the REF AMP, then look at the currents in the R-2R ladder.
V0
RREF
R
2R
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ATmega168 DAC0800
Simple 8 bit DAC for the Arduino ATmega168
int i=0;
void setup()
{
DDRD = 0xff;
}
void loop()
{
PORTD = i;
if(i==256) i=0;
i++;
}
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(Analog-to-Digital Converter A/D A2D)
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Analog-to-digital conversion
Analog comparator = 1-bit A-to-D
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ADC Techniques
Digital Ramp ADC Counter method)
Successive Approximation
- High Speed, Medium Resolution
- Very high-speed conversion
Dual Slope
- Slow Speed, High Resolution26
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Digital Ramp ADC Counter method)
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This simplest ADC uses a binary counter as the register
A Start pulse resets the counter & disables the And gate
With all 0 0 volts
Since VAX < VA, the op-amp EOC output will be High
When Start returns Low, the AND gate is enabled.
As the counter advances, the DAC output, VAX, increases one step at a time
This continues until VAX reaches a step that just exceeds
VA by about VT. EOC is then Low disabling the AND.
The A/D Conversion is now complete and the contents of the counter are the
digital representation of VA.
The digital data is lost at the next START pulse.
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Successive Approximation ADC (SAC)ADC ATMega168
AVCC
Atmega168
VCC AVCC.
AVCC PC0-PC5
analog AVCC
low
pass filter inductor
capacitor.
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AREF
AREF 100% (
analog 1024)
Analogue Input
Atmega168 analog 6 PC0 to PC5.
digital I/O analogue input
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Registers
Atmega168
Register Description
ADMUX ADC Multiplexer Selection Register
ADCSRA ADC Control and Status Register A
ADCSRB ADC Control and Status Register B
DIDR0 Digital Input Disable Register 0
ADCL ADC Data Register Low
ADCH ADC Data Register High
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ADMUX
The ADMUX register allows you to control:
The Reference Voltage
Left adjustment of results (used for 8 bit results)
Selection of input channel
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ADMUX ADC Multiplexer Selection Register ADMUX
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ADMUX : ADLAR MUX3:0
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ADLAR: ADC Left Adjust Result
= left adjust
= right adjusted
ADCL and ADCH The ADC Data Register
: MUX : : Analog Channel Selection Bits
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Atmega
V V
ADCSRA ADC Control and Status Register A
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ADEN: ADC Enable
= enables the ADC
= ADC is turned off turnoff
ADCSRA ADC Control and Status Register A
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Bit ADSC: ADC Start Conversion
Single Conversion mode
=
Free Running mode
= start the first conversion. The first conversion
ADC enabled
ADCSRA ADC Control and Status Register A
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ADATE: ADC auto trigger enable
= Autotrig ADC
ADTS ADCSRB
= Auto trig
ADCSRA ADC Control and Status Register A
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ADIF: ADC Interrupt Flag
ADCL/ADCH
I SREG
clear
ADCSRA ADC Control and Status Register A
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ADIE: ADC Interrupt Enable
= Enable
0 = Disable
When this bit is written to one and the I-bit in SREG is set, the ADC
Conversion Complete Interrupt
is activated.
ADCSRA ADC Control and Status Register A
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: ADPS : : ADC Prescaler Select Bits
ADCL and ADCH The ADC Data Register
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ADEN = 1 ADC
ADATE = 0 Auto trig
ADPS2- = 001 XTAL/8
ADCSRA = 0b10000001;
ADCSRA = (1<<ADEN)|(0<<ADATE);
ADCSRA |= (0<<ADPS2)|(0<<ADPS1)|(1<<ADPS0);
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C
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/----- Includes ------/#include <avr io h> AVR device-specific IO definitions#include <avr interrupt h> Interrupt Service routine
#define F_CPU 8000000UL 8 MHz#include <util delay h> header file implement simple delay loops
#include lib_UART c Use Module USART
#define Vadc 1024 1024 10-bit Resolution
----- delay_ms ------void delay_ms uint16_t i{
for ;i > 0; i--_delay_ms 1 ;
} 46
int main(void){
ADCSRA = (1<<ADEN)|(0<<ADATE); // ADC Enable & Auto Trigger DisableADCSRA |= (0<<ADPS2)|(0<<ADPS1)|(1<<ADPS0); // XTAL/8ADCSRA = while(1){ // Infinite loop; define here the
//Aref,left adjust, select ADC0 (bit 2=0 bit 1 = 0 bit 0 = 0)ADMUX = 0b0000000; ADCSRA |= (1<<ADSC); // ADC Start Conversionwhile (!(ADCSRA &(1<<ADIF))); // Wait Coversion completes adc0 = ADCW; // Read ADC_delay_ms(10);
}}
Arduino
analogReference(type)
analogRead()
analogWrite() - PWM
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analogReference(type)
Configures the reference voltage used for analog input (i.e. the value used as the top of the input range). The options are:
DEFAULT: the default analog reference of 5 volts (on 5V Arduino boards) or 3.3 volts (on 3.3V Arduino boards)
INTERNAL: an built-in reference, equal to 1.1 volts on the ATmega168 or ATmega328 and 2.56 volts on theATmega8 (not available on the Arduino Mega)
INTERNAL1V1: a built-in 1.1V reference (Arduino Mega only)
INTERNAL2V56: a built-in 2.56V reference (Arduino Mega only)
EXTERNAL: the voltage applied to the AREF pin (0 to 5V only) is used as the reference.
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analogRead()
Description
Reads the value from the specified analog pin. The Arduino board contains a 6 channel (8 channels on the Mini and Nano, 16 on the Mega), 10-bit analog to digital converter. This means that it will map input voltages between 0 and 5 volts into integer values between 0 and 1023. This yields a resolution between readings of: 5 volts / 1024 units or, .0049 volts (4.9 mV) per unit. The input range and resolution can be changed using analogReference().
It takes about 100 microseconds (0.0001 s) to read an analog input, so the maximum reading rate is about 10,000 times a second.
Syntax
analogRead(pin)
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Arduino
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int analogPin = 3; // potentiometer wiper (middle terminal) connected
to analog pin 3 // outside leads to ground and +5V
int val = 0; // variable to store the value read
void setup()
{
Serial.begin(9600); // setup serial
}
void loop()
{
val = analogRead(analogPin); // read the input pin
Serial.println(val); // debug value
}
analogWrite() - PWM
analogWrite(pin, value)
Parameters
pin: the pin to write to.
atmega168 D D D D D D11
value: the duty cycle: between 0 (always off) and 255 (always on).
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PWM analogWrite
#define pwm_1 3
#define pwm_2 5
#define pwm_3 6
#define pwm_4 9
#define pwm_5 10
#define pwm_6 11
void setup()
{
analogWrite(pwm_1, 10);
analogWrite(pwm_2, 50);
analogWrite(pwm_3, 100);
analogWrite(pwm_4, 150);
analogWrite(pwm_5, 200);
analogWrite(pwm_6, 250);
}
void loop()
{
}
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