I am trying to modify the aerodynamics around my car, and before I do anything I need data. I need to measure the air pressure at a couple of hundred points around the car.
I have been doing a LOT of research, and doing the data gathering with a manometer tube on the seat next to me while barreling down the highway seems a bit...... dangerous? Inefficient to say the least.
What I am thinking of doing is placing 4 pressure sensors in specific locations, reading the values into a spreadsheet and then repeating, for a couple of times.
I purchased a computer and a learning kit for me and my son to learn how to do stuff and I want to use this opportunity to develop our first project.
Has anyone done something like this? Pointers and advice is really needed.
I am on the mechanical side of the aircraft industry, so the building of stuff is a piece of cake. The moment electrical stuff is added, I lose the plot completely.
Any help will be greatly appreciated.
Regards
Alexander
This is what dataloggers are for.
That link will let you save data from an arduino to an SD card with a timestamp. You will also need an arduino (Adafruit Feather) and pressure sensors.
There are other arduino datalogger shields, but that's the only one I've actually used. Or you can purchase prebuilt dataloggers off the shelf. It's a pretty mature technology.
I plan on buying 5 HKD BAROMTRC SENSR-BMP280-3.3. They seem to sensitive enough to measure increments of inches of water. I was pointed to a website with an arduino program and wiring to read one sensor at a time. I will order the Hardware after payday and then get one sensor to work. Then will modify the program to read 5 at a time.
Where can I look for the programming to add the data logger?
First, get the hardware. Second get the one sensor working.
I will ask for advice again as soon as I have that sorted.
Then you understand the need for a controlled environment, not an open highway with a multitude of random wind and air movements. Do like the Wright brothers and make a wind tunnel and a model of your car with sensors.
Hi @alexvanwyk I suggest you to go for a raspberry Pi or something similar. Through raspberry Pi you can directly obtain your data in a csv file or Google Sheets {The best} which can be easily accessed. This will ensure the effort to setup your requirements will remain low and you can spend time on mechanical stuff. There are a lot of tutorials online on how you can achieve the same.
Forum members correct me if wrong.
I will look into the different computer options. My main point is that I already have the arduino computer. They are ridiculously expensive here, probably because the market is limited to a very small group, and the exchange rate is horrendous.
As for the wind tunnel.....
I have given it a large amount of thought. Its what keeps me up at night.
Most of the information on the internet is focused at high performance and high speed.
I drive a station wagon that I use off road a lot. In fact I bought it specifically for its reputation as a good offroader, and I have been to places where the average 4X4 driver is scared to go. I also haul the family on long distance trips very frequently.
So it boils down to....
1: The stupid plastic panel Under the engine has disintegrated with time.
2: I have time and a bucket load of fibreglass that is going to expire soon.
3: I plan on measuring the real world conditions around the car and then making one change, and then measuring the difference. My daily commute consists of a stretch of highway that is perfectly flat, straight, smooth and undisturbed by any buildings, or even trees for that matter. I can gather data twice everyday for a week, spend the weekend modifying and then repeating.
I dont expect to see any spectacular changes, but even a 5% improvement will make a massive difference over the distances I drive. And I have to replace the panel, so I can just as well do it properly and learn a new skillset.
I bought a XGZP6857D010KPGPN sensor
Its a -10kpa to +10kps module that will measure the range of pressure i need.( I hope)
There is a code for the Arduino computer on the website where i bought it specifically for that sensor but.....
They don't define what pins are the input pins.
I have ground, and 3.3V connected.
where do I plug the other 2 pins in.
SCL is the clock
SDA is the Data.
Code is copied below.
//Libraries
#include <Arduino.h>
#include <Wire.h>
//constants & variables
bool error=0; //reading error variable (not used in this sketch)
float pressureKPA=0.0; //declare pressure KPa variable
float pressureCMH2O=0.0; //declare pressure cmH2O variable
float temperatureC=0.0; //declare temperature Celsius variable
float temperatureF=0.0; //declare temperature Fahrenheit
long startMillis=0; //start sampling milliseconds time
const long period=2000; //time between samples in milliseconds
//hardware settings
//functions
bool readCFSensor(float &temp, float &press,byte sensorAddress);
void setup() {
Serial.begin(115200); //begin serial port
Wire.begin(); //begin i2c bus
delay(200); //wait for electronics
}
void loop() {
Serial.println(""); //
Serial.println(F("-------------------------------------------------------------------------")); //samples division
Serial.println(""); //
startMillis=millis(); //save the starting time
error = readCFSensor(temperatureC,pressureKPA,0x6D); //start conversion and read on pressure sensor ad 0x6D address
Serial.println("Temperature *C: " + String(temperatureC,1)); //print *C temperature
temperatureF= temperatureC * 1.8 + 32; //*C to *F conversion
Serial.println("Temperature *F: " + String(temperatureF,1)); //print *F temperature
Serial.println("Pressure KPa: " + String(pressureKPA,3)); //print KPa pressure
pressureCMH2O = pressureKPA * 10.1972; //KPa to cmH2O conversion
Serial.println("Pressure cmH2O: " + String(pressureCMH2O,2)); //print cmH2O pressure
while((millis()-startMillis) < period); //waits until period done
}
bool readCFSensor(float &temp, float &press,byte sensorAddress) {
byte reg0xA5=0;
Wire.beginTransmission(sensorAddress); //send Start and sensor address
Wire.write(0xA5); //send 0xA5 register address
Wire.endTransmission(); //send Stop
Wire.requestFrom(sensorAddress,byte(1)); //send Start and read 1 byte command from sensor address
if(Wire.available()){ //check if data is available on i2c buffer
reg0xA5 = Wire.read(); //read 0xA5 register value
}
Wire.endTransmission(); //send Stop
Serial.println("Register 0xA5 read: " + String(reg0xA5,HEX)); //for debugging purposes
reg0xA5 = reg0xA5 & 0xFD; //mask 0xA5 register AND 0xFD to set ADC output calibrated data
Wire.beginTransmission(sensorAddress); //send Start and sensor address
Wire.write(0xA5); //send 0xA5 register address
Wire.write(reg0xA5); //send 0xA5 regiter new value
Wire.endTransmission(); //send Stop
Serial.println("Write 0xA5 register: " + String(reg0xA5,HEX)); //for debugging purposes
Wire.beginTransmission(sensorAddress); //send Start and sensor address
Wire.write(0x30); //send 0x30 register address
Wire.write(0x0A); //set and start combined conversion
Wire.endTransmission(); //send Stop
Serial.println("Write 0x0A on 0x30 register and start conversion"); //for debugging purposes
byte reg0x30 = 0x08; //declare byte variable for 0x30 register copy (0x08 initializing for while enter)
while((reg0x30 & 0x08) > 0) { //loop while bit 3 of 0x30 register copy is 1
delay(1); //1mS delay
Wire.beginTransmission(sensorAddress); //send Start and sensor address
Wire.write(0x30); //send 0x30 register address
Wire.endTransmission(); //send Stop
Wire.requestFrom(sensorAddress,byte(1));//send Start and read 1 byte command from sensor address
if(Wire.available()){ //check if data is available on i2c buffer
reg0x30 = Wire.read(); //read 0x30 register value
}
Wire.endTransmission(); //send Stop
Serial.println("Register 0x30 read: " + String(reg0x30,HEX)); //for debugging purposes
}
unsigned long pressure24bit; //declare 32bit variable for pressure ADC 24bit value
byte pressHigh=0; //declare byte temporal pressure high byte variable
byte pressMid=0; //declare byte temporal pressure middle byte variable
byte pressLow=0; //declare byte temporal pressure low byte variable
Wire.beginTransmission(sensorAddress); //send Start and sensor address
Wire.write(0x06); //send pressure high byte register address
Wire.endTransmission(); //send Stop
Wire.requestFrom(sensorAddress,byte(3)); //send Start and read 1 byte command from sensor address
while(Wire.available() < 3); //wait for 3 byte on buffer
pressHigh = Wire.read(); //read pressure high byte
pressMid = Wire.read(); //read pressure middle byte
pressLow = Wire.read(); //read pressure low byte
Wire.endTransmission(); //send Stop
Serial.print(String(pressHigh)); //for debugging purposes
Serial.print("," + String(pressMid)); //for debugging purposes
Serial.print("," + String(pressLow)); //for debugging purposes
pressure24bit = pressure24bit | pressHigh;
pressure24bit = pressure24bit & 0x000000FF;
pressure24bit = pressure24bit << 8;
pressure24bit = pressure24bit | pressMid;
pressure24bit = pressure24bit & 0x0000FFFF;
pressure24bit = pressure24bit << 8;
pressure24bit = pressure24bit | pressLow;
pressure24bit = pressure24bit & 0x00FFFFFF;
Serial.print(":" + String(pressure24bit)); //for debugging purposes
int temp16bit=0; //declare 16bit variable for temperature ADC value
byte tempHigh=0; //declare temperature high byte variable
byte tempLow=0; //declare temperature low byte variable
Wire.beginTransmission(sensorAddress); //send Start and sensor address
Wire.write(0x09); //send temperature high byte register address
Wire.endTransmission(); //send Stop
Wire.requestFrom(sensorAddress,byte(2)); //send Start and read 1 byte command from sensor address
while(Wire.available() < 2); //wait for 2 byte on buffer
tempHigh = Wire.read(); //read temperature high byte
tempLow = Wire.read(); //read temperature low byte
Wire.endTransmission(); //send Stop
Serial.print(" - " + String(tempHigh)); //for debugging purposes
Serial.print("," + String(tempLow)); //for debugging purposes
temp16bit = tempHigh * 256 + tempLow; //merge of 16bit temperature ADC value
Serial.println(":" + String(temp16bit)); //for debugging purposes
temp = float(temp16bit)/256; //real Celsius temperature calculation
if(pressure24bit > 8388608) { //check sign bit for two's complement
press = (float(pressure24bit) - float(16777216)) * 0.0000078125; //KPa negative pressure calculation
}
else { //no sign
press = float(pressure24bit) * 0.0000078125; //KPa positive pressure calculation
}
return 0;
}
I assume that you have discovered that for a Uno SDA is pin A4 and SCL is pin A5 but be aware that there is a trap for the unwary on some Uno boards. They have pins explicitly labelled SDA and SCL as well as separate pins labelled A4 and A5. However, both pairs are connected to the same pair of pins on the processor so you cannot use say SDA and A4 pins for two different purposes in the same sketch
I got all the hardware and fitted, and I got some readings that I can use.
I have edited the program to give me data in a format that I can make work and 1 out of 5 data runs I can make conclusions on what to modify on the car.
This brings me to 3 questions where I ask for help and pointers in the right direction.
1: Is there a tutorial / class on how to write the programs?
I did computer programming as a subject at school, 25 years ago. ( good grief I am getting old) There are a lot of lines of code that I dont understand the reasoning for and even the basic format is not very clear. I would like to understand that better
2: I am reading 1 digital input at a time. Can I read more that one sensor at a time? do I need other hardware to combine the readings to the computer?
3: I am doing a data run with the computer plugged into the Arduino board, then displaying the readings on the serial screen. At the end of the run I copy the screen and paste in word, then convert to .TXT and import to excell and then have to convert to meaningfull readings before analysing.
Its working, but not optimal. The computer is on the back seat of the car while barreling down the highway. So start the program, check that it is reading, jump in the front, hit the gas, do the run, stop, hop out and then stop the computer.
Suggestions please?
Thinking a data logger? ( adding complications to the program and cost to the hardware, but not too a big concern. It will just add time to the project as I buy when I have spare cash )
Is there a way to read the data into a file on the computer so I dont need to copy and paste?
Its clunky, Its complicated, Its fiddly. Part of the challenge is to learn a skill, and to play with the car.
There are a lot of lines of code that I dont understand the reasoning for and even the basic format is not very clear. I would like to understand that better