I've got the following code snippet in the setup() function:
...
unsigned int a0val;
unsigned int a0total = 0;
...
for (i = 0; i < 1000; i++) {
a0val = analogRead(A0);
Serial.println(a0val);
a0total += a0val;
}
Serial.println(a0total);
...
This is done to baseline the analog value at startup to account for different types of sensors being used. One type may read 0 and another may read some non-zero value. The point is to have a starting point reference by averaging 1000 readings at startup time. 1000 is obviously overkill, I'll cut back later.
Now, with 1000 readings somewhere between 128 and 130, I expect a0total to be around 129,000. However, the total consistently comes out less than half that number, like 63,722 in one example. It's not even half, it's less than that.
Another example: I add up the first 500 readings when they are all around 350-352, and the total came out to 43614. It looks like wrap-around, but I'm using unsigned int for both values so that can't be happening.
So to me it almost looks like "a0total += a0val" is not updating every loop, but that doesn't make sense either.
What am I missing?
Thanks,
Ron
You are missing size of unsigned int on this platform. It is 16bits and therefore the maximum value is 65535.
Related
Little backstory:
I'm currently doing this project that deals with using two cars, called block A and B, which block B has to maintain a distance of 10 cm from block A using PID, PD, PI, or P. I'm using a PID. Block B uses an Arduino whereas Block A is controlled by the user by hand. Block B uses a unipolar stepper motor as the actuator and an ultrasonic sensor to sense the distance. My professor wants the motor to move in both directions and have varying speeds (slow, medium, and fast). I'm using brett's PID since I have used it before in my previous labs.
Problem:
I have an issue with how to create varying speeds for block B like intuitively I know that I want the B should move for example, fast if the car is greater than 20 cm, medium if the car is between 20cm and 14cm, and slow if it's between 14cm and 10cm. But I just can't use the input value retrieved from the sensor directly to control the motor as it would make it an open system. So I used the error retrieved from Brett's PID code to control the stepper motor. So far, I have gotten the directions to work by setting the myPID.SetOutputLimits(-800,800);. But as it tried to use the error to control the speed it would be impossible because the error always fluctuates at a specific distance. For example at 12cm, I would get either 800 or around 300. I'm currently confused about how to implement control of the speed of my stepper motor through PID and any help regarding this issue will be appreciated.
Code:
Code was through Arduino IDE.
#include "SR04.h"
#include <Stepper.h>
#include <PID_v1.h>
#define TRIG_PIN 7
#define ECHO_PIN 6
//intialization of Ultrasonic sensor
SR04 sr04 = SR04(ECHO_PIN,TRIG_PIN);
long s;
//intializing motor variables
int stepsPerRevolution = 2048;
int motorSpeed = 6;
Stepper myStepper (stepsPerRevolution, 8, 10, 9, 11);
//Declared PID variables
double Setpoint = 10; //desired temp value
double Input; //thermsitor
double Output; //DC motor
double Error;
//defined variables for PID parameters
double Kp=100, Ki=10, Kd=1;
//PID equation
PID myPID(&Input, &Output, &Setpoint, Kp, Kd, Ki, REVERSE);
void setup(){
Serial.begin(9600);
//setting PID
myPID.SetMode(AUTOMATIC);
myPID.SetOutputLimits(-800,800);
//speed intialized
myStepper.setSpeed(motorSpeed);
}
void loop(){
s=sr04.Distance();
Input = s;
myPID.Compute();
Error = Input - Setpoint;
//Serial.print(Input);
//Serial.print(",");
//Serial.println(Setpoint);
Serial.println(Output);
//Serial.print(",");
//Serial.println(Error);
Error = Output;
//Away from Block B
if (0<Error<800){
myStepper.setSpeed(motorSpeed);
myStepper.step(-300);
} //slow speed
if (Error>=800){
myStepper.setSpeed(motorSpeed*2);
myStepper.step(-128);
} //fast speed
//Towards Block B
if (-800<Error<0) {
myStepper.setSpeed(motorSpeed);
myStepper.step(128);
} //slow speed
if (Error<=-800) {
myStepper.setSpeed(motorSpeed*2);
myStepper.step(128);
}//Fast speed
}
What you need to do is calcuulate how much you need to change your current speed to minimize the error in distance.
Your calculation for error is not in the right place.
void loop()
{
long s=sr04.Distance();
Input = s; // using global variables to pass values to your PID
// is not a good idea. Use function parameters instead.
// You are storing a 32 bit value in a 16 bit variable!!!
// That's only the start of your problems.
myPID.Compute();
Error = Input - Setpoint; //
Since we're starting with a major design flaw, I'll have to assume you'll fix that and change your PID code to accept and compute long integers both as input value as a function parameter, and as the type of its return value..
What you want to do is compute the PID from the error in distance from your set point, and then modulate the current speed accordingly. PIDs work best when used directly, using 7 speeds (1 stopped, 3 forward/3 backwards) is possible, but I don't think it'll give better results, I'll leave the exercise to you.
I haven't tried this, I don't have any cars on hand. This is a skeletoon of how I'd go about it. Tuning the PID should be what takes you the longest.
//...
// speeds are in RPMs.
long curSpeed = 0;
const long MAX_SPEED = XXX; // whatever you max speed is for your car.
const long MIN_NEG_SPEED = -XXX; // whatever you max speed is for your car going reverse.
const long MIN_SPEED = XXX; // below this absolute speed, we're stopped.
const int SLICE_TIME = 10; // time between readings and adjustments, in ms.
// you'll need to adjust this according to you minimum speed, and steps per turn.
const long STEPS_PER_TURN = 200; // change to whatever you steps/turn value is.
// you'll need to limit the output of your PID to match the acceleration your
// motors can handle for your particular car.
// returns the number of steps to run for our slice time.
long Steps(int speed)
{
if (-MIN_SPEED <= speed && speed <= MIN_SPEED)
return 0;
// compute number of steps for our slice time.
// choose slice time and minimum speed wisely!!
long steps = (SLICE_TIME * (speed * STEPS_PER_TURN)) / (60000L);
// for very low speeds. I've added this, because I'm unsure of the
// time domain behaviour of stepper library with less than 2 steps
if (-1 <= steps && steps <= 1)
{
if (speed < 0)
return -2;
else
return 2;
}
return int(steps);
}
void loop()
{
// You may want to filter the sr04 readings with a median of 5
// filter to limit input noise.
// You want to keep the car at a distance of 'set_point'
// from the leading car. distance_error is the error you want to
// minimize to zero by using the PID, and that's what should be
// the PID input.
//
// The way this works. We are rolling at speed curSpeed, we
// measure the error in distance from our set_point, feed that
// to the PID, then accelerate or decelerate by subtracting
// the output of the PID from the current speed.
//
// Note: you can add or subtract the PID to/from the current speed,
// the sign of the PID depends on you coefficients and sensor.
// I've used subtraction here because that's how you express
// negative feedback mathematically. In real life, we'll use what
// best fits our needs. Usually it's the operation that makes P
// positive.
long distance_error = sr04.Distance() - setPoint;
long pid_out = myPID.Compute(distance_error);
// increment or decrement the current speed to try and reduce the error.
long speed = curSpeed - pid_out; // As usual, PID coefficients do matter
// for this to work well.
if (speed > MAX_SPEED)
speed = MAX_SPEED;
if (speed < MIN_NEG_SPEED)
speed = MIN_NEG_SPEED;
curSpeed = speed;
if (speed < 0)
speed = -speed;
myStepper.setSpeed(speed); // modulate speed
int steps = Steps(curSpeed);
if (steps)
myStepper.step(steps); // keep rolling.
}
I haven't tried to compile it either, so this may not compile as is. But most of the tricks and traps are covered, and this should give you a head start, if you want to go the PID route. But I think your professor will really wonder where that one came from :) Still, you should try and make it run, for fun.
The other way, without a PID, and using set speeds is much more straightforward. It may also be closer to what the is required by the exercise. The distance between cars will vary a bit more, of course. And it does not use a PID at all.
const int MAX_SPEED = 3;
int speed = 0; // value range is [-MAX_SPEED, +MAX_SPEED]
long RPMS[MAX_SPEED + 1] = { 0, 200, 400, 800 }; // in RPMs, assuming average speed will be around 400, in this case.
// For 3 speeds, the difference between speeds cannot be higher than max acceleration.
// You can add as many speeds as desired. More speeds = more precision.
const long STEPS_PER_TURN = 200; // change to whatever you steps/turn value is. MUST be 200 or more.
const int STEPS = STEPS_PER_TURN / 100; // 3.6° between speed adjustment.
// it is very small right now, so
// you will want to play with this value.
// this threshold gives some control over aceleration.
// and 'hardness' of distance tracking.
const long THRESHOLD = 0;
void loop()
{
// get the error in distance.
long distance_error = sr04.Distance() - setPoint;
// modulate speed.
if (distance_error > THRESHOLD)
++speed;
if (distance_error < -THRESHOLD)
--speed;
if (speed > MAX_SPEED)
speed = MAX_SPEED;
if (speed < -MAX_SPEED)
speed = -MAX_SPEED;
long rpm = RPMS[(speed < 0) : -speed : speed];
if (rpm)
{
myStepper.setSpeed(rpm);
myStepper.setSpeed((speed < 0) ? -STEPS : STEPS)
}
}
For this code, you must choose speeds and STEPS value that will give you an acceleration without misssed steps.
I'm sending data through USART on an Arduino Due. I'm currently filling a buffer so the data gets sent just when a buffer is full.
The data I'm putting into the buffer is a lookup table of different wave shapes with 12 bits of depth (values from 0 to 4095). So I'm putting into the buffer values that are 2 bytes of depth, and the most significant byte is always 0.
My problem is that everyonce in a while a whole wave period gets shifted a byte (every value gets multiplicated by 256). The error is unpredictable: it might happen on the 2nd or 3rd period to be sent, but it happens soon. I tried slower baudrates, or adding two stopbits, but nothing fixes it. The relevant chunk of the code:
const int buflen = 2048;
int i = 0;
int j = 0;
int k = 1;
int wave = 0;
short buff[buflen];
volatile PROGMEM short sintab[3][512] = ...//there's no need to paste here the lookup tables
void setup(void){
Serial3.begin(115200, SERIAL_8N2);
}
void loop(void) {
buff[j]= sintab[wave][i];
i+= k;
j++;
if (i>511){
i-=512;
}
if (j>=buflen){
byte* bytePointer =(byte*)buff;
for (int l=0; l<=buflen; l++){
Serial3.write(bytePointer[l]);
Serial3.flush();
}
int j = =0;
}
I'm checking the received data on both a serial monitor and a python program that stores the received values and print them. I think its weird that the error never happens in the middle of a wave: a one or two waves are copied good on the buffer and then a whole value gets shifted. How could I fix this?
It looks like the issue is not in this block of code where you're writing the data out to your USART port, rather in storing the data to that array. When you have this byte offset occur, can you validate that the data in your array is as you expect it to be?
Edit:
Change
for (int l=0; l<=buflen; l++)
to
for (int l=0; l< buflen; l++)
so you enumerate over the set 0 to 511, which is 512 elements. Now you are enumerating an additional element, which is reading data from an unexpected memory location and returning whatever is there (likely the next byte of your static structure).
From what I understand, the range of QModbusDataUnit::InputRegisters is range 0-65535 which is unsigned short.
The method to read 1 unit of inputregisters is as follows:
QModbusDataUnit readUnit(QModbusDataUnit::InputRegisters, 40006, 1);
The value of that will be in the reply, i.e : int value = result.value(0);
My question is that what if I have to read a value of unsigned int which is much larger of the range of 0 to 4,294,967,295.
How can I retrieve that value?
As you stated, Modbus input registers are 16 bit unsigned integers. So without some type of conversion they are limited to the range: 0 - 65535. For 32-bit unsigned values it is typical (in Modbus) to combine two registers.
For example, the high 16-bits could be stored at 40006 and the low 16-bits at 40007.
So, if you were reading the value 2271560481 (0x87654321 hex), you would read 34661 (0x8765) from address 40006 and 17185 (0x4321 hex) from location 40007. You would then combine them to give you the actual value.
I don't know the Qt Modbus code, but expanding on your example code you can probably read both values at the same time by doing something like this:
readUnit(QModbusDataUnit::InputRegisters, 40006, 2);
and combine them
quint32 value = result.value(0);
value = (value << 16) | result.value(1);
I was wondering if you could help me use NEON intrinsics to optimize this mask function. I already tried to use auto-vectorization using the O3 gcc compiler flag but the performance of the function was smaller than running it with O2, which turns off the auto-vectorization. For some reason the assembly code produced with O3 is 1,5 longer than the one with O2.
void mask(unsigned int x, unsigned int y, uint32_t *s, uint32_t *m)
{
unsigned int ixy;
ixy = xsize * ysize;
while (ixy--)
*(s++) &= *(m++);
}
Probably I have to use the following commands:
vld1q_u32 // to load 4 integers from s and m
vandq_u32 // to execute logical and between the 4 integers from s and m
vst1q_u32 // to store them back into s
However i don't know how to do it in the most optimal way. For instance should I increase s,m by 4 after loading , anding and storing? I am quite new to NEON so I would really need some help.
I am using gcc 4.8.1 and I am compiling with the following cmd:
arm-linux-gnueabihf-gcc -mthumb -march=armv7-a -mtune=cortex-a9 -mcpu=cortex-a9 -mfloat-abi=hard -mfpu=neon -O3 -fprefetch-loop-arrays name.c -o name
Thanks in advance
I would probably do it like this. I've included 4x loop unrolling. Preloading the cache is always a good idea and can speed things up another 25%. Since there's not much processing going on (it's mostly spending time loading and storing), it's best to load lots of registers, then process them as it gives time for the data to actually load. It assumes the data is an even multiple of 16 elements.
void fmask(unsigned int x, unsigned int y, uint32_t *s, uint32_t *m)
{
unsigned int ixy;
uint32x4_t srcA,srcB,srcC,srcD;
uint32x4_t maskA,maskB,maskC,maskD;
ixy = xsize * ysize;
ixy /= 16; // process 16 at a time
while (ixy--)
{
__builtin_prefetch(&s[64]); // preload the cache
__builtin_prefetch(&m[64]);
srcA = vld1q_u32(&s[0]);
maskA = vld1q_u32(&m[0]);
srcB = vld1q_u32(&s[4]);
maskB = vld1q_u32(&m[4]);
srcC = vld1q_u32(&s[8]);
maskC = vld1q_u32(&m[8]);
srcD = vld1q_u32(&s[12]);
maskD = vld1q_u32(&m[12]);
srcA = vandq_u32(srcA, maskA);
srcB = vandq_u32(srcB, maskB);
srcC = vandq_u32(srcC, maskC);
srcD = vandq_u32(srcD, maskD);
vst1q_u32(&s[0], srcA);
vst1q_u32(&s[4], srcB);
vst1q_u32(&s[8], srcC);
vst1q_u32(&s[12], srcD);
s += 16;
m += 16;
}
}
I would start with the simplest one and take it as a reference for compare with future routines.
A good rule of thumb is to calculate needed things as soon as possible, not exactly when needed.
This means that instructions can take X cycles to execute, but the results are not always immediately ready, so scheduling is important
As an example, a simple scheduling schema for your case would be (pseudocode)
nn=n/4 // Assuming n is a multiple of 4
LOADI_S(0) // Load and immediately after increment pointer
LOADI_M(0) // Load and immediately after increment pointer
for( k=1; k<nn;k++){
AND_SM(k-1) // Inner op
LOADI_S(k) // Load and increment after
LOADI_M(k) // Load and increment after
STORE_S(k-1) // Store and increment after
}
AND_SM(nn-1)
STORE_S(nn-1) // Store. Not needed to increment
Leaving out these instructions from the inner loop we achieve that the ops inside don't depend on the result of the previous op.
This schema can be further extended in order to take profit of the time that otherwise would be lost waiting for the result of the previous op.
Also, as intrinsics still depend on the optimizer, see what does the compiler do under different optimization options. I prefer to use inline assembly, which is not difficult for small routines, and give you more control.
I'm trying to create a program, using Qt (c++), which can record audio from my microphone using QAudioinput and QIODevice. I made a research and I came up with an example located on the this page. This example does what I need.
Now, I am trying to create an audio waveform of the recorded sound. I want to extract audio amplitudes and save them on a QList. To do that I use the following code:
//Check the number of samples in input buffer
qint64 len = m_audioInput->bytesReady();
//Limit sample size
if(len > 4096)
len = 4096;
//Read sound samples from input device to buffer
qint64 l = m_input->read(m_buffer.data(), len);
if(l > 0)
{
//Assign sound samples to short array
short* resultingData = (short*)m_buffer.data();
for ( i=0; i < len; i++ )
{
btlist.append( resultingData[ i ]);
}
}
m_audioInput is QAudioinput | m_buffer is QBytearray | m_input is QIODevice | btlist is QList
I use the following QAudioFormat:
m_format.setFrequency(44100); //set frequency to 44100
m_format.setSampleRate(44100); //set sample rate to 44100
m_format.setChannels(1); //set channels to mono
m_format.setSampleSize(16); //set sample sze to 16 bit
m_format.setSampleType(QAudioFormat::SignedInt ); //signed integer sample
m_format.setByteOrder(QAudioFormat::LittleEndian); //Byte order
m_format.setCodec("audio/pcm"); //set codec as simple audio/pcm
When I print my QList, using qWarning() << btlist.at(int), I get some positive and negative numbers which represents my audio amplitudes. I used Microsoft Excel to plot the data and compare it with the actual sound waveform.
(EDIT BASED ON THE OP COMMENT)
I am drawing the waveform using QPainter in Qt like this
for(int i = 1; i < btlist.size(); i++){
double x1 = (i-(i/1.25))-0.2;
double y1 = btlist.at(i-1);
double x2 = i-(i/1.25);
double y2 = btlist.at(i);
painter.drawLine(x1,y1,x2, y2);
}
The problem is that I also get lots of zeros (0) in my QList between the amplitude data like this, which if I draw as a waveform they are a straight line, which is not normal because it causes corruption to my waveform.
My question is why is that happening? What these zeros (0) represent? Am I doing something wrong? Also, is there a better way to extract audio amplitudes from QBytearray?
Thank you.
The drawline method you are using take integer values. Which means most of the time both of your x indexes will be the same. By simplifiyng your formula the x value at a given i is (i/5.0). By itself it is not an issue because the lines will be superposed, and it is a perfect way of drawing (just to make sure that's what you want to do).
The zero you see can be perfectly valid. They represent silence.
The real issue is that the range of your 16 bits PCM values is [-32767 , 32768]. I doubt that the paint device you are using cover this range. You need to normalize your y-axis. Moreover, it seems taht the qt coordinated system doesn't have negative values (edit: Nevermind the negatives, its says logical coordinates are converted).
For instance, convert your pcm values using :
((btlist.at(i) / MAX_AMPLITUDE + 1.0) / 2) * paintDevice.height();
Edit:
Btw, you are not using l, which is the real amount of data you read. If it is inferior to len, you will read invalid values at the end of your buffer, possibly read garbage\ read zeros\crash.
And your buffer is a byte buffer. And you iterate using a short pointer. So whether you use l or len the maximum size need to be divided by two. This is probably the cause of the ling line of zero in your picture.
for ( i=0; i < l/2; i++ )
{
btlist.append( resultingData[ i ]);
}