Hello! So, I need some help with displaying what my Serial Monitor says onto my LCD screen. Every time I do it, it does display on my LCD screen, it's just that instead of displaying the proper letters, it shows random letters (not symbols, just letters), and also the incorrect numbers. I'm completely new to Arduino, and I'm doing this for a school project that's due tomorrow (very terrible time to do this, I know). I'm practically done with my school project, this is the last thing I need to do.
I'm using example code from the MH-Z CO2 Sensors library, and modifying it a little bit. The code displays perfectly fine when untouched (on the Serial Monitor). I've been reading up on other forums, but nothing's helped me as much. Please let me know if I need to display the code!
By the way, I'm using an Arduino Uno R3 (in case you needed to know).
Yes that would definitely help. To do that, start a reply, press a Return key to start a new paragraph, click the CODE icon in the toolbar that appears above your reply text (picture below) then paste the code.
Until then all we can do is guess, but I happen to know lcd.print("Hello"); won’t do anything useful unless lcd.init(); is called first.
I am pretty new to the Arduino too, but I have been doing lots of things with that popular two line LCD display, so it’s fresh in my mind and I’d love to help you.
#include <SoftwareSerial.h>
#include <MHZ.h>
#include <LiquidCrystal.h>
const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
// pin for pwm reading
#define CO2_IN 10
// pin for uart reading
#define MH_Z19_RX 4 // D7
#define MH_Z19_TX 0 // D6
MHZ co2(MH_Z19_RX, MH_Z19_TX, CO2_IN, MHZ19B);
void setup() {
Serial.begin(9600);
pinMode(CO2_IN, INPUT);
delay(100);
Serial.println("MHZ 19B");
// enable debug to get addition information
// co2.setDebug(true);
if (co2.isPreHeating()) {
Serial.print("Preheating");
while (co2.isPreHeating()) {
Serial.print(".");
delay(5000);
}
Serial.println();
}
}
void loop() {
Serial.print("\n----- Time from start: ");
lcd.print(millis() / 1000);
Serial.println(" s");
int ppm_pwm = co2.readCO2PWM();
lcd.print("PPMpwm:");
lcd.print(ppm_pwm);
Serial.println("\n------------------------------");
delay(5000);
}
In the original code, there was UART and some temperature thing, but the PPM is the only one that really works so I'm focusing on that (I deleted the other two).
… then you have to add the line lcd.begin() before it will do anything.
From the above, it “Initializes the interface to the LCD screen, and specifies the dimensions (width and height) of the display. begin() needs to be called before any other LCD library commands.”
(I added the boldface)
Try this. I only added the few lines with ***** characters in the comments.
#include <SoftwareSerial.h>
#include <MHZ.h>
#include <LiquidCrystal.h>
const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
// pin for pwm reading
#define CO2_IN 10
// pin for uart reading
#define MH_Z19_RX 4 // D7
#define MH_Z19_TX 0 // D6
MHZ co2(MH_Z19_RX, MH_Z19_TX, CO2_IN, MHZ19B);
void setup() {
Serial.begin(9600);
pinMode(CO2_IN, INPUT);
delay(100);
Serial.println("MHZ 19B");
lcd.begin(16,1); // ***** 16 columns, 1 row
lcd.clear(); // ***** clear the display, cursor upper left
lcd.print("hello, world!"); // ***** print something so we know it's working
delay(5000); // ***** allow time to read it before proceeding
// ***** get rid of the delay() when everything is working *****
// enable debug to get addition information
// co2.setDebug(true);
if (co2.isPreHeating()) {
Serial.print("Preheating");
while (co2.isPreHeating()) {
Serial.print(".");
delay(5000);
}
Serial.println();
}
}
void loop() {
Serial.print("\n----- Time from start: ");
lcd.home(); // ***** position the cursor at upper left
lcd.print(millis() / 1000);
Serial.println(" s");
int ppm_pwm = co2.readCO2PWM();
lcd.print("PPMpwm:"); // ***** these will go right after the " s"
lcd.print(ppm_pwm);
Serial.println("\n------------------------------");
delay(5000);
}
So, not long after I tested the code, it started getting all weird (the text was starting to become gibberish), and now the text won't display on the screen at all. It used to work well, not sure what happened..
I replaced a few wires (and stopped doubling-up wires) and the text still doesn't show up on my LCD screen. The serial monitor shows that the code is working, but I guess the screen isn't taking the input? I can send some more pictures if you need me to.
I rewired everything (apparently my wiring was wrong), and now the screen works. Also, super duper sorry about the image quality.. My phone camera is baaad. Testing out the code again, it.. err..
This is my first attempt trying out the code, it randomly did this:
Now, it looks like this. I want to see if I can remove the random numbers at the start, but that would be a bit of a hassle and I don't want to wreck it again, now that it's the due day for my project..
A little tip: always use I2C LCD displays. You'll save a few pins (only two are used!) and a few connections. Simply buy LCDs with a pre-soldered I2C backpack, so you won't have to solder the pins (current LCDs have very poor quality soldering...).
PS: and since you have a breadboard to make multiple connections, no more doubling up on wires!
