Random characters generated by LCD during serial.read()

Question

I am using the following codes to print characters on LCD display....

#include <LiquidCrystal.h>
const int rs = 8, en = 9, d0 = 4, d1 = 5, d2 = 6, d3 = 7;
LiquidCrystal lcd(rs, en, d0, d1, d2, d3);
void setup() {
 lcd.begin(16, 2);
 Serial.begin(9600);
}
void loop() {
 if (Serial.available()) {
 delay(100);
 lcd.clear();
 while (Serial.available() > 0) {
 lcd.write(Serial.read());
 }
 }
}

but in the end it is generating an unwanted character also.. enter image description here

kindly help me with the problem

• Juraj: I guess, it is the newline character. What line end is Serial Monitor set to send?
• aaa: Does 'lcd.write("Hello");' work? You should check if the problem is on the serial or on the LCD.
• Gyan_mishra: yes it works perfectly
• aaa: @Gyan_mishra in that case, it doesn't appear to be a problem on the display's side. Is the same character generated when you do: "lcd.write("\r\n");"? Or choose "No line ending" in the Arduino serial monitor.
• Gyan_mishra: thanks for help @Paul .... the problem was exactly the same...

Answer 1

The character to the right of the 'A' on your LCD display does not correspond to any of the built-in character bitmap definitions (either on a EU or Chinese display). This random pattern is likely one of the 8 programmable character bitmaps supported by the LCD that has not been defined yet (ASCII codes 0 to 7).

So, you're likely sending the LCD a character with a value between 0 and 7. It's probably a good idea to filter out invalid characters before attempting to display them on your LCD.

Filtering Example:

char c = Serial.read();
if ((c >= 32) && (c <= 128))
 lcd.write(c);

• Gyan_mishra: could you tell me, how to filter out invalid characters before attempting to display
• Jeff Wahaus: I've updated the answer to illustrate a simple filtering example. Take a look at an ASCII table to understand why the numbers I chose are significant.
• Gyan_mishra: thank you @jeff, for providing me such an excellent example of filtering.. it worked