Help Required - RPM Counter With Analog input

Forum 2005-2010 (read only) Software Troubleshooting
1

Hello to all,
Can any anyone help me?
I am trying to make a RPM counter using a hall sensor (UNG3503UA, connected to analog pin 0), by detecting when the voltage drops just below 1/2 of the operational output voltage.
Would anyone mind looking over my very amateur code, to see where I have gone wrong,

The intro screen is loading up ok, then it displays the rpm text and 0,
but when i apply a pulsing voltage (5v) to the input, nothing happends

Any help is very much appreciated,
Nick

#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2); // Initialize the library with the numbers of the interface pins

int analogPin = A0; // Pin that the Hall sensor is attached to
int threshold = 400; // A defined threshold level that's in the range of the analog input
int hallState = 0; // Value used to store state of Sensor
int oldHallstate = 0; // This Stores he last Hallstate value
int rpm = 0; // Value used to store state of Sensor
long startTime; // Start time for timing
long elapsedTime; // Elapsed time for stop watch
int test;

void setup()
{
lcd.begin(16, 4); // Set up the LCD's number of columns and rows:
lcd.setCursor(0, 0); // Sets the posiion of the cursor
lcd.print("x"); // Print a message to the LCD.
lcd.setCursor(0, 1); // Sets the posiion of the cursor
lcd.print("x"); // Print a message to the LCD.
lcd.setCursor(0, 2); // Sets the posiion of the cursor
lcd.print("x"); // Print a message to the LCD.
lcd.setCursor(0, 3); // Sets the posiion of the cursor
lcd.print("x"); // Print a message to the LCD.
delay(4000); // Delay for opening message
lcd.begin(16, 4); // Clear Screen
lcd.setCursor(5, 1); // Sets the posiion of the cursor
lcd.print("RPM"); // Print a rpm lable to the LCD.
}

void loop()
{
{
test = analogRead(0); // read the analog value of the hall sensor
if (test >= threshold) // if the analog value is high enough, turn state to high
{
hallState = 1;
}

else {
hallState = 0;
}

}

{

if (hallState == 0 && oldHallstate == 1)
{
startTime = millis();
delay(5);
oldHallstate = hallState;
}

else if (hallState == 0 && oldHallstate == 1)
{
elapsedTime = millis() - startTime;
oldHallstate = hallState;
}
}

rpm =((int)(elapsedTime / 1000));
lcd.setCursor(10, 1); // Sets the posiion of the cursor
lcd.print(rpm); // Print rpm value

}

2 
int [glow]analogPin[/glow] = analogRead([glow]analogPin[/glow]);
   if   ([glow]analogPin[/glow] >= threshold)           // if the analog value is high enough, turn state to high

In the if statement, which analogPin are you referring to? The global one or the local one?

3

I'm afraid that I have confused myself totally,
To be honest I'm not sure

4

Defining local variables and global variables with the same name is almost never a good idea, or necessary.

Variable names should reflect the meaning of the contents. analogPin is not a very good name for either purpose. The value in the variable and the context in which it is used indicates that the global variable IS an analog pin. But, a name like hallSensorPin says a lot more about the use of that variable. In the same way, hallSensorValue tells you a lot about the contents of the variable, and can lead to spotting incorrect usage when it happens.

int hallSensorPin = analogRead(hallSensorValue);

would be spotted as an error right away, while

int hallSensorValue = analogRead(hallSensorPin);

would look perfectly reasonable. Now, there could still be errors, like hallSensorPin having a value of 3 while the sensor is connected to pin 5, but that is a lot less likely an event.

I am trying to make a RPM counter using a hall sensor (UNG3503UA, connected to analog pin 0), by detecting when the voltage drops just below 1/2 of the operational output voltage.

Do you have a link to this sensor? Typically, the output of a hall effect sensor is not linear. The applications for which a hall effect sensor are used, such as detecting and counting rotational motion, do not require linear output. Therefore, it seems strange to be using a hall effect sensor this way.

In general, the hall effect sensor is connected to a digital pin. The presence of a pulse will be detected when the voltage rises above 60% of the reference voltage. The exact value is not all that critical, since the sensor is so non-linear, the difference in time between 50% and 60% will hardly be detectable.

And, if time IS a factor, the slow response time of the ADC that is measuring the input will nullify that effect, anyway.

5 
    if       (hallState == 0 && oldHallstate == 1)
             {
                startTime = millis();
                delay(5);
                oldHallstate = hallState;   
             }
    
    else if  (hallState == 0 && oldHallstate == 1)
             { 
                elapsedTime = millis() - startTime;
                oldHallstate = hallState;  
             }

Have I been smoking something or is this basically:

if X

else if X

How is it supposed to reach elapsedTime = ?