Arduino Rocket Engine Static Test Stand

static_test_stand.ino

/*
Model Rocket Engine Dynamometer - Nick Cinquino 9/1/15 
V.5 Original 10Kg loadcell Modified from Nathan Seidle, SparkFun Electronics, November 19th, 2014
Output data in grams (g). There are 101.97 gram-force per Newton, for conversion. 
Your calibration factor may be very positive or very negative. 
It all depends on the setup of your individual loadcell, and the direction the sensors deflect from zero state. 
Need to experiment!
Hack the HX711 board to set pin 15 high, for 80 samples per second.
This example code uses bogde's excellent library: https://github.com/bogde/HX711 
bogde's library is released under a GNU GENERAL PUBLIC LICENSE
Arduino pin 2 - HX711 Clock
pin 3 - Serial Data In
5V - VCC
GND - GND
Yellow LED on pin 13, igniter transistor/relay on pin 11, momentary pushbutton on pin 12.
Most any pin on the Arduino Uno will be compatible with DOUT/CLK.
The HX711 board can be powered from 2.7V to 5V so the Arduino 5V power is fine.
*/
#include "HX711.h"
#include <LiquidCrystal.h> 
LiquidCrystal lcd(8,9,4,5,6,7);
const int buttonPin = 12; 
const int ledPin = 13; 
const int igniterPin = 11; 
int buttonState = 0; 
// start sequence button 
//LED indicator and/or buzzer 
//igniter transistor circuit
HX711 scale;
float calibration_factor = -560; //-560 works for my 10kg loadcell.
void setup() {
    pinMode(buttonPin, INPUT);
    pinMode(igniterPin, OUTPUT);
    pinMode(ledPin, OUTPUT);
    Serial.begin(9600);
    Serial.println("HX711 Rocket Motor Dynamometer, V.5");
    Serial.println("Affix motor nozzle up. Place igniter in nozzle. Move away from test stand.");
    Serial.println("Press start button to initialize ignition sequence."); 
    lcd.begin(16, 2);
    lcd.clear();
    lcd.setCursor(0,0);
    lcd.print(" MODEL ROCKET");
    lcd.setCursor(0,1);
    lcd.print(" DYNAMOMETER");
    delay(2000);
    scale.set_scale();
    scale.tare(); //Reset the scale to 0
    long zero_factor = scale.read_average(); //Get a baseline reading
    //This can be used to remove the need to tare the scale.
    //Useful in permanent scale projects. 
    Serial.print("Zero factor: ");
    Serial.println(zero_factor); 
    Serial.println(" ");
}

void loop() {
    lcd.clear();
    lcd.setCursor(0,0);
    lcd.print(" Rocket Dyno"); 
    lcd.setCursor(0,1);
    lcd.print(" STDBY " ); 
    scale.set_scale(calibration_factor); 
    lcd.print(scale.get_units(),1); 
    lcd.print(" g");
    delay(500);
    buttonState = digitalRead(buttonPin); 
    if (buttonState == HIGH) {
        lcd.clear();
        lcd.setCursor(0,0);
        lcd.print(" Rocket Dyno");
        lcd.setCursor(0,1);
        lcd.print(" STAND CLEAR!"); 
        Serial.println("IGNITION SEQUENCE ACTIVATED!");
        for (int i=0; i <= 50; i++){ 
            digitalWrite(ledPin, HIGH); 
            delay (100);
            digitalWrite (ledPin,LOW); 
            delay (100);
        }

        lcd.clear();
        lcd.setCursor(0,0);
        lcd.print(" Rocket Dyno"); 
        lcd.setCursor(1,1);
        lcd.print(" AQUIRING DATA"); 
        digitalWrite(igniterPin, HIGH); 
        Serial.print("Start time, ms: "); 
        Serial.print (millis()); 
        Serial.println(" "); 
        Serial.println();

        for (int i=0; i <= 800; i++){ 
        //800 samples at 80sa/sec = 10 seconds theoretical 
            scale.set_scale(calibration_factor); 
        //Adjust to the calibration factor 
            Serial.print(scale.get_units(), 1);
            Serial.println();
        }

        Serial.println(); 
        Serial.print("Stop Time, ms: "); 
        Serial.print(millis()); 
        digitalWrite (ledPin,LOW); 
        digitalWrite (igniterPin,LOW); 
        Serial.println();
    } 

}