// ver 1.8 24 March 2019
// Mega2560 version
//Note the word 'pause' used as 'delay' is a function & could cause confusion
//Note TriggerPin must be debounced, else it plays havoc. - look at link below...
//https://hackaday.com/2015/12/09/embed-with-elliot-debounce-your-noisy-buttons-part-i/
#define DEBUG false //set to true for debug output, false for no debug ouput
#define Serial if(DEBUG)Serial
#include <TimerOne.h> // https://github.com/PaulStoffregen/TimerOne
#include <Wire.h> // built in libray
#include <LiquidCrystal_I2C.h> // built in library
LiquidCrystal_I2C LCD(0x27, 20, 4); // set the LCD address to 0x27
// how to wre LCD https://www.youtube.com/watch?v=ZtwFpFIS1_0
// trigger timer Variables seup here.
volatile long pauseTime = 850000; // time between triggering and flash firing uS
volatile int timeoutFlag = 0; // set to 1 if trigger pushed and timeout not expired
const int led = LED_BUILTIN; // the pin with on-pcb LED Uno pin 13, Nano pin 16
const int triggerPin = 18; // user input to start pause (interrupt 5)
const int flashLed = 23; // output to flashLed, lights when flash fires
const int pauseLed = 22; // output to pauseLed, lights between triggering and firing
const int coarsePausePot = A8; // user input coarse pause pot
const int finePausePot = A9; // user input fine pause pot
const int timeoutPot = A10; // user input time between triggering and re-triggering
long int pause = 620; // user input pot to set pauseTime
long int oldPause = 620; // last reading from user input pot
long int coarsePause = 500; // var to store user input
long int finePause = 120; // var to store user input
int val; // misc variable
int ledState = LOW; // LED status (on or off)
int timeout = 100; // timeout before sytem can trigger again mS
int timeoutOld = 10;
// splash vars
const int solPin = 7; // assign pin 7 to solenoid
const int camPIN = 6; // assign pin 6 to camera
const int dropOnePot = A1; // assign pin A1 to potentiometer 1
const int dropTwoPot = A2; // assign pin A2 to potentiometer 2
const int dropThreePot = A3; // assign pin A3 to potentiometer 3
const int dropDelayOnePot = A4; // assign pin A4 to potentiometer 4
const int dropDelayTwoPot = A5; // assign pin A5 to potentiometer 5
const int startBUTTON = 11; // assign pin 11 to startBUTTON
const int intTriggerSel = 10; // assign pin 10 to trigger select
int solDelayOne; // declare solDelayOne variable
int solDelayTwo; // declare solDelayOne variable
int camDEL; // declare camDEL variable
int dropOne; // declare dropOne variable
int dropTwo; // declare dropTwo variable
int dropThree; // declare dropTwo variable
int dropOneOld; // declare dropOne variable
int dropTwoOld; // declare dropTwo variable
int dropThreeOld; // declare dropTwo variable
int solDelayOneOld; // declare solDelayOne variable
int solDelayTwoOld;
int buttonSTATE = HIGH; // set buttonSTATE variable to HIGH
boolean internalTrigger = true; // select if drop button also starts trigger timer
void setup() { // put your setup code here, to run once: *************************
//trigger timer
pinMode(led, OUTPUT); // set on-pcb LED pin as output
pinMode(triggerPin, INPUT_PULLUP); // user input pin to start pause
pinMode(coarsePausePot, INPUT); // user input pot to set coarse pauseTime
pinMode(finePausePot, INPUT); // user input pot to set fine pauseTime
pinMode(timeoutPot, INPUT); // user input pot min time before next trigger allowed
pinMode(intTriggerSel, INPUT_PULLUP); // user input select how flash is fired when using drop
pinMode(flashLed, OUTPUT); // setup flashLed - lights when flash fires
pinMode(pauseLed, OUTPUT); // setup pauseLed - lights between triggering and flash firing
Timer1.initialize(500000); // setup timer 500000uS
Timer1.stop(); // stop timer as not needed yet
Timer1.attachInterrupt(timer1Expired); // setup interrupt timer1Expired to run for pauseTime uS
attachInterrupt(digitalPinToInterrupt(triggerPin), trigger, FALLING); // setup interrupt
// splash
pinMode(solPin, OUTPUT); // set solPin to output
pinMode(camPIN, OUTPUT); // set camPIN to output
pinMode(dropOnePot, INPUT); // set potentiometer 1 as input
pinMode(dropTwoPot, INPUT); // set potentiometer 2 as input
pinMode(dropThreePot, INPUT); // set potentiometer 3 as input
pinMode(dropDelayOnePot, INPUT); // set potentiometer 4 as input
pinMode(startBUTTON, INPUT_PULLUP); // set startBUTTON as input
Serial.begin(9600); // debug setup output to screen
LCD.init();
LCD.backlight();
LCD.clear(); // clear LCD screen
LCD.setCursor(0, 0); // position cursor on LCD
LCD.print(" TriggerTimer "); // print to LCD
LCD.setCursor(0, 1); // reset the cursor position
LCD.print("FLPa"); // Flash Pause
LCD.setCursor(10, 1); // reset the cursor position
LCD.print("TO"); // TimeOut
LCD.setCursor(0, 2); // reset the cursor position
LCD.print("Drp"); // print the line "Drp" drop
LCD.setCursor(0, 3); // reset the cursor position
LCD.print("Pau"); // print the line "Pau" pause
}
// ISRs go here *************************
// ISR when triggered, sets Timer1 pauseTime
void trigger (void) {
if (timeoutFlag == 0) { // check timeout time has expired before allowing new trigger
Timer1.setPeriod(pauseTime); // activate timer pause counter
digitalWrite(pauseLed, HIGH);
timeoutFlag = 1; // set timeout flag to stop second activation
}
}
// ISR is called at end of Timer1 period.
void timer1Expired(void) {
digitalWrite(pauseLed, LOW); // update state of pasuselength LED
digitalWrite(flashLed, HIGH); // fire flashgun
Timer1.stop(); // stop timer as no longer needed
}
// end of ISRs ***************************************************
void loop() { // put your main code here, to run repeatedly:**********************
// read and format triggertimer user input
coarsePause = analogRead(coarsePausePot); // readuser input from coarse pause pot
finePause = analogRead(finePausePot); // readuser input from coarse pause pot
coarsePause = map(coarsePause, 0 , 1023, 1, 800); // map input to mS
finePause = map(finePause, 0 , 1023, 0, 50); // map input to mS
pause = (coarsePause + finePause); // add coarse & fine delays to give total pause
// triggertimer - Update Pausetime & LCD if user has changed input
if (pause != oldPause) { // if user changed pause, update
noInterrupts(); // turn off interrupts as variable is used in ISR
pauseTime = pause * 1000; // convert to uS and update var used in interrupt
interrupts(); // turn on interrupts
oldPause = pause; // update to check next time round
LCD.setCursor(5, 1); // position LCD cursor
LCD.print(" "); // blank out old reading
LCD.setCursor(5, 1); // position LCD cursor
LCD.print(pause); // print updated pauseTime to LCD
} // end if
// triggertimer - Update timeout & LCD if user has changed input
timeout = analogRead(timeoutPot); // read user input from timeOut pot
timeout = map(timeout, 0 , 1023, 0, 500); // map result
timeout = (timeout * 10); // convert to mS
if (timeout != timeoutOld) { // if user changed timeut, update
timeoutOld = timeout; // update to check next time round
LCD.setCursor(13, 1); // position LCD cursor
LCD.print(" "); // blank out old reading
LCD.setCursor(13, 1); // position LCD cursor
LCD.print(timeout); // print updated pauseTime to LCD
}
// splash Update drop & delay times & LCD if user has changed input
dropOne = analogRead(dropOnePot); // read analogue value from potentiometer 1
dropOne = map(dropOne, 0, 1023, 10, 100); // use map to increase accuracy of pot
if (dropOne != dropOneOld) { // only update LCD if value has changed
dropOneOld = dropOne; // copy var to check for change in if-loop
LCD.setCursor(5, 2); // set cursor position as bottom left
LCD.print(" "); // print 3 spaces to keep LCD clean
LCD.setCursor(5, 2); // reset cursor position
LCD.print(dropOne); // print the calculated time value dropOneval
} // end if
dropTwo = analogRead(dropTwoPot); // read analogue value from potentiometer 2
dropTwo = map(dropTwo, 0, 1023, 9, 100); // use map to increase accuracy of pot
if (dropTwo == 9) dropTwo = 0; // if below 10, set to 0, no second drop
if (dropTwo != dropTwoOld) { // only update LCD if value has changed
dropTwoOld = dropTwo; // copy var to check for change in if-loop
LCD.setCursor(9, 2); // reset cursor position
LCD.print(" "); // print 3 spaces to keep LCD clean
LCD.setCursor(9, 2); // reset cursor position
LCD.print(dropTwo); // print the calculated time value dropTwoval
} // end if
dropThree = analogRead(dropThreePot); // read analogue value from potentiometer 2
dropThree = map(dropThree, 0, 1023, 9, 100); // use map to increase accuracy of pot
if (dropThree == 9) dropThree = 0;
if (dropThree != dropThreeOld) { // only update LCD if value has changed
dropThreeOld = dropThree; // copy var to check for change in if-loop
if (dropThree == 9) dropThree = 0; // if below 10, set to 0, no second drop
LCD.setCursor(13, 2); // reset cursor position
LCD.print(" "); // print 3 spaces to keep LCD clean
LCD.setCursor(13, 2); // reset cursor position
LCD.print(dropThree); // print the calculated time value dropTwoval
} // end if
solDelayOne = analogRead(dropDelayOnePot); // read analogue value from potentiometer 3
solDelayOne = map(solDelayOne, 0, 1023, 20, 200); // use map to increase accuracy of pot
if (solDelayOne != solDelayOneOld) { // only update LCD if value has changed
solDelayOneOld = solDelayOne; // copy var to check for change in if-loop
LCD.setCursor(5, 3); // set cursor position as bottom line, 9 characters from left
LCD.print(" "); // print 3 spaces to keep LCD clean
LCD.setCursor(5, 3); // reset cursor position
LCD.print(solDelayOne); // print the calculated time value dropThreeval
} // end if
solDelayTwo = analogRead(dropDelayTwoPot); // read analogue value from potentiometer 3
solDelayTwo = map(solDelayTwo, 0, 1023, 20, 200); // use map to increase accuracy of pot
if (solDelayTwo != solDelayTwoOld) { // only update LCD if value has changed
solDelayTwoOld = solDelayTwo; // copy var to check for change in if-loop
LCD.setCursor(9, 3); // reset cursor position
LCD.print(" "); // print 3 spaces to keep LCD clean
LCD.setCursor(9, 3); // reset cursor position
LCD.print(solDelayTwo); // print the calculated time value dropThreeval
} // end if
// Test for user input. If drop button pressed, start drop sequence
buttonSTATE = digitalRead(startBUTTON); // test state of start button
if ((buttonSTATE == LOW) && timeoutFlag == 0) { // if pressed, start drop sequence
Timer1.setPeriod(pauseTime); // activate timer pause counter for flash delay
digitalWrite(pauseLed, HIGH);
LCD.setCursor(17, 1);
LCD.blink();
timeoutFlag = 1;
digitalWrite(solPin, HIGH); // set solPin to HIGH - open the solenoid for first drop
delay(dropOne); // delay for time value dropOne - first drop size
digitalWrite(solPin, LOW); // set solPin to LOW - close the solenoid
if (dropTwo != 0) { //test if second drop reqired
delay(solDelayOne); //delay for time value solDelayOneval
digitalWrite(solPin, HIGH); //set solPin to HIGH - open solenoid for second drop
delay(dropTwo); //delay for time value dropTwo - second drop size
digitalWrite(solPin, LOW); //set solPin to LOW - close the solenoid
}
if (dropThree != 0) { //test if third drop reqired
delay(solDelayTwo); //delay for time value solDelayOneval
digitalWrite(solPin, HIGH); //set solPin to HIGH - open solenoid for third drop
delay(dropThree); //delay for time value dropThree - third drop size
digitalWrite(solPin, LOW); //set solPin to LOW - close the solenoid
}
}
val = digitalRead(flashLed); // read flashpause
if (val == HIGH) { // if flash has fired...
Serial.println("Flash has Fired"); // debug
delay(100); // delay before releasing flash contacts
digitalWrite(flashLed, LOW); //.........and open contacts
delay(timeout); //.....timeout delay....
timeoutFlag = 0; //reset timeoutFlag
LCD.setCursor(17, 1);
LCD.noBlink();
}
else { // debug
Serial.println("not fired"); // debug
} // debug
// debug print out variables to screen
if (DEBUG) {
Serial.print("finePause: ");
Serial.println(finePause);
Serial.print("coarsePause: ");
Serial.println(coarsePause);
Serial.print("pause: ");
Serial.println(pause);
Serial.print("pauseTime: "); // debug output to screen
Serial.println(pauseTime); // debug output to screen
Serial.print("timeout: "); // debug output to screen
Serial.println(timeout); // debug output to screen
Serial.println(" ");
delay(500);
}
}
// end of void loop **********************
)
for the most useful guide I have found 
to Talk Photography!
Let's horrify those experts 
There’s obviously noise or or something corrupting the signal, maybe due to my lousy soldering, I’m not sure. The temptation is to throw it on the bonfire and start again. But as I know from being a coder for a fair few years now, the frustration only makes the eventual success all that much sweeter!