Ok, I'm trying to make my Arduino display voltages for 12v, 5v and 3v lines. I've got a 16x2 LCD.
First, is it possible to get all 3 displayed at once? As in the top line being "3.3V 5V 12V" spaced evenly, then the bottom line being the 3 readings. I know they won't update all at the same time, but that's no big deal.
Second, if it's not possible, how do I need to set it up so when the unit is turned on it displays a welcome message, then with each button press it switches between 3v, 5v and 12v?
here's my code so far for the second setup (with only 3v and 5v for now, still have to figure out how to read 12v without frying something):
/*Arduino Controlled Voltage Monitor
Code by Will Lyon 12/5/2010
Code for project Power House on TBCS
http://www.thebestcasescenario.com*/
#include <LiquidCrystal.h>
#include <math.h>
int counter = 0; //Add counter
int buttonPin = 2; //Attach button to pin 2
// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
void setup() {
pinMode(buttonPin, INPUT); //Set button pin to input
lcd.begin(16, 2); //Set up the LCD's number of columns and rows
lcd.print(" POWER HOUSE");
lcd.setCursor(0, 1);
lcd.print("Desktop Pwr Unit");
}
void loop()
{
digitalRead(buttonPin); //Read the button pin
if (buttonPin = HIGH) //If the button is pressed
{
counter + 1; //Advance to next mode
if(counter == 2) //Reset count if over max mode number
{
counter = 1;
}
}
if(counter == 1)
{
lcd.print("3.3 Volt Line");
lcd.setCursor(0, 1);
lcd.print(analogRead(2));
}
else if(counter == 2)
{
lcd.print("5 Volt Line");
lcd.setCursor(0, 1);
lcd.print(analogRead(0));
}
}
It displays the opening message, but when the button is pressed nothing happens.
First, is it possible to get all 3 displayed at once?
Yes
how do I need to set it up so when the unit is turned on it displays a welcome message,
In the setup() part do a LCD.print("Welcome SXR"); followed by a delay(2000); or so
As you only have 16 positions I would use the 1st line for the measured voltages and the second line as a message/status line:
0123456789012345 = position
-----------------------------
3.1V 4.8V 12.3V = line 0
All systems OK = line 1
(code not compiled or tested)
void loop()
{
bool OK = true;
lcd.setCursor(0, 0);
float f = analogRead(2) * 3.3 / 1024; // 3.3 => 9.9
lcd.print(f, 1); // print float with one decimal
if (f > 3.3) OK = false
lcd.setCursor(0, 6);
f = analogRead(0) * 5.0 / 1024; // 5.0 => 9.9
lcd.print(f, 1);
if (f > 5.0) OK = false;
lcd.setCursor(0, 11);
f = analogRead(0) * 12.0 / 1024; // 12.0 => 25.0
lcd.print(f, 1);
if (f > 12.0) OK = false;
lcd.setCursor(1,0);
if (OK) lcd.print("All systems OK");
else lcd.print("Warning !!!");
delay(100);
}
Note: the code above assumes the max voltage is 3.3 cq 5.0 volt . Think it might be better to have both max 9.9 volt (100 different values, with 0.1 accuracy) then you still have enough positions to display but a larger range.
Option, leave out the V for voltage and use this to have an additional digit of accuracy. => lcd.print(f, 2);
0123456789012345 = position
-----------------------------
3.11 4.85 12.32 = line 0
All systems OK = line 1
both instances it says "expected '(' before '=' token"
also, it doesnt need to be any kind of a warning. when I'm building circuits and testing parts I just want to be able to tell if the 5v line is actually only running at 4.7v, etc
now the hard(er) part. How do I hook an analog pin to a 12v line without frying the arduino?
This is actually quite simple. Use a voltage divider (google hint). Make sure both resisters are of the correct wattage to match the current drop across them.
Works great! except for the fact that my 5v is showing 3.44 lol
float f = analogRead(0) * 3.3 / 1024; Change 3.3 in 5.0
You probably want to know when the voltage is to high too, that means that you should prepare your software to display high ranges (and your hardware to read them.
To read 12 Volt you could build a Voltage divider:
+12V ------| R1 | ----+----- | R2 | --- GND
COnnect Arduino analog at +
R1 : R2 = 7 : 5
However as you might expect higher voltages e.g. 15 or even 25 Volt you need to change the values of R1 : R2 = 20 : 5 so the AnalogIn (and the whole Arduino) will not be fried.
Best way to do this is to take two resitors with the approx the right ratio e.g. 20K and 5K together 25K. Put a known voltage 12Volt to it (check with calibrated voltmeter) and adapt the N in the formula f = analogread(0) * N /1024 so the Arduino displays the right value. Another way is to have one fixed resistor and one variable (potmeter) and one could calibrate the voltage displayed.
Note if the 12Volt comes from a car battery better check out postings of GrumpyMike as he has warned several people lately
I used a 51K resistor from the 12v to the input to arduino, and a 68K from there to ground for the divider circuit.
That brings too much voltage to the Arduino Analog IN pin you should swap them. So the +12 V drops 7 Volts to the arduino pin which drops 5Volts to GND
Zzzzzzz
