Hi all,

I'm trying to design and build a Rev. Counter for a Windmill to monitor the speed of the sails.
I'm using a Microchip Pic16F84 and a 1602 LCD display.
The unit needs to count from 0 to 12 RPM.
However when a send the Ascii value 8 and 9 the display goes blank, all other numbers (0 to 7) are OK.
I have replaced 8 and 9 with A and B and the display displays them.
I assumed the display was faulty and purchased another one from a different supplier but that does the same thing.

Any of you clever people got any ideas?

Regards,
Phil

 

post your code

 

Hi phil,
Welcome to AAC.
Please post your PIC code and a circuit diagram.
E

 

post your code

Attached is the code I wrote to test the display count to 9.

Regards

Phil

 

Sorry I don't have a Circuit Diagram as my Schematic Editor does not have a model for the 1602 but it is connected as follows:-

Vo 10K pot to Vcc
Rs Port A bit 0
Rw Ground
E Port A bit 1
D0 to D7 to port B D0 to D7
Led+ Vcc via a 22 ohm
Led- Ground
Gnd Ground
Vcc Vcc

The Code is attached to the post above this one.

Regards

Phil

 

Sorry, I don't do PIC ASM.
However, I notice some inefficiencies in your code and I can make suggestions to help fix the problem.

Firstly, whenever you have to repeat the same code sequence, look for ways to create a single subroutine to simplify the coding.

For testing, create code to send one and only one character. Test it with the problematic characters.

Once that problem is resolved, create a subroutine to send a character string. In other words, you only need one call to a subroutine to display any text of any number of characters.

 

There is a prog in assembly on the Nigel Goodwin tutoriol site for digital diaplay
http://www.winpicprog.co.uk/pic_tutorial.htm
Also https://www.datsi.fi.upm.es/docencia/DMC/servo1/HowtouseLCD1.pdf

 

Check the wiring and voltages of the data bus between PIC and LCD. Maybe D3 is open or stucked at GND.

 

I am not sure how your "ASCII codes" look like
but 01H to 09H are non-printable characters. If some of them give an apparently valid result on the LCD, but those last two no, I would start revising what you are actually sending to the display controller.

 

It's likely you swapped D7 and D3 for the codes. Among characters 0-9,A,B, only 8 and 9 have D3=1, for a typical 1602 LCD character map.

 

There are all possible errors to be made. A systematic check of all steps will reveal the error.
Are you using 4-bit mode or 8-bit mode?

Here is my code snippet for 4-bit mode written in C.

void LCD_init(void)
{
  LCD_ir(0x28);         // dual line, 4 bits
  LCD_ir(0x06);         // increment mode
  LCD_ir(0x0C);         // cursor turned off
  LCD_ir(0x10);         // cursor right
  LCD_ir(0x01);         // clear display
}

void LCD_ready(void)
{
  char busy;
  LCD_DDR = 0xF0;
  LCD_RW = 1;
  LCD_RS = 0;
  do
  {
    LCD_E  = 1;
    // high 4 bits read first
    // busy flag is D7 of LCD = bit 3 of P2IN
    busy = (LCD_IN & 0x08);
    LCD_E  = 0;
    LCD_E  = 1;
    LCD_E  = 0;
  } while (busy);
  LCD_OUT = 0;
  LCD_DDR = 0xFF;
}

void LCD_ir(char ch)
{
  LCD_ready();
  //LCD_RS = 0;      // not needed      // select instruction register
  //LCD_RW = 0;     // not needed
  LCD_OUT |= ((ch >> 4) & 0x0F);
  LCD_E = 1;
  LCD_E = 0;
  LCD_OUT = 0;
  LCD_OUT |= (ch & 0x0F);
  LCD_E = 1;
  LCD_E = 0;
}

void LCD_dr(char ch)
{
  LCD_ready();
  LCD_RS = 1;        // select data register
  //LCD_RW = 0;      // not needed
  LCD_OUT |= ((ch >> 4) & 0x0F);
  LCD_E = 1;
  LCD_E = 0;
  LCD_OUT = 0;
  LCD_RS = 1;
  LCD_OUT |= (ch & 0x0F);
  LCD_E = 1;
  LCD_E = 0;
}

void LCD_txt(char *s)
{
  while(*s) LCD_dr(*s++);
}

 

hi C,
He is using 8bit LCD.
When I run it in Oshonsoft I don't see what he is describing.
I get 'a T 1 3 5 7' in that sequence.

E

BCF PORTA,0 ;SEND COMMANDS
MOVLW B'00110000' ;8 BIT MODE 1 LINE 5x7 DOTS
CALL SEND2LCD
MOVLW B'00000001' ;CLEAR DISPLAY
CALL SEND2LCD
MOVLW B'00000010' ;RETURN HOME
CALL SEND2LCD
MOVLW B'00001100' ;DISPLAY ON NO CURSORR
CALL SEND2LCD

 

Thanks for all your help but I have now given up.
I modified the program to just display the number 8 (see attached) and checked all the data pins at the LCD with the 'scope. The ASCII code was correct for 8 (00111000) and good levels.
I then tried to do it using characters but several numbers were not displayed, one being TWO. The T and the W are displayed at the initial message (PLEASE WAIT) and the O displayed for ONE but when TWO - blank screen.
I now believe the LCD display technology is flawed and will have to resort to 7 Segment displays which is a shame because I hoped to run the unit from a 9 volt battery but as the 7 Segment displays take heavy current this will not be practical.

Regards
Phil.

 

Don’t give up so easily. I am certain that this can be fixed.

 

Thanks for all your help but I have now given up.
I modified the program to just display the number 8 (see attached) and checked all the data pins at the LCD with the 'scope. The ASCII code was correct for 8 (00111000) and good levels.
I then tried to do it using characters but several numbers were not displayed, one being TWO. The T and the W are displayed at the initial message (PLEASE WAIT) and the O displayed for ONE but when TWO - blank screen.
I now believe the LCD display technology is flawed and will have to resort to 7 Segment displays which is a shame because I hoped to run the unit from a 9 volt battery but as the 7 Segment displays take heavy current this will not be practical.

Regards
Phil.

I am sure that testing with sequences of different binary values every time could help you find what is wrong.

Sure it's your call to change the type of display, BUT, in doing so, you won't have learnt anything or increased your ability to troubleshoot a failure or advance on a new design. Just dodging...

Not to speak about the waste of time / efforts from YOU (and AAC members).

 

You learn more from your mistakes than from first time successful builds.

 

Hi all,

I'm trying to design and build a Rev. Counter for a Windmill to monitor the speed of the sails.
I'm using a Microchip Pic16F84 and a 1602 LCD display.
The unit needs to count from 0 to 12 RPM.
However when a send the Ascii value 8 and 9 the display goes blank, all other numbers (0 to 7) are OK.
I have replaced 8 and 9 with A and B and the display displays them.
I assumed the display was faulty and purchased another one from a different supplier but that does the same thing.

Any of you clever people got any ideas?

Regards,
Phil

You can find these links useful.
https://www.engineersgarage.com/displaying-ascii-characters-on-lcd-with-pic-microcontroller/
https://en.wikipedia.org/wiki/Hitachi_HD44780_LCD_controller
https://cdn.sparkfun.com/assets/9/5/f/7/b/HD44780.pdf
https://www.pcbway.com/project/shareproject/Universal_HD44780_LCD_interface_e3f2df0c.html

 

Don’t give up so easily. I am certain that this can be fixed.

MrChips, I didn't give up easily but have run out of ideas, I don't know what to do next!!!

 

MrChips, I didn't give up easily but have run out of ideas, I don't know what to do next!!!

No problem. We will work you through this tomorrow.

 

There are four common issues with trying to get 1602 displays to work.

1) Adjusting and setting the contrast voltage properly.
2) Initializing the LCD.
3) Proper time delays when sending control signals.
4) Proper power supply decoupling.

Start by attempting to display a single character such as ’A’ or ‘0’.
The next step would be display a sequence of characters using an iterative loop.

For example, ’0’ to ‘9’.
‘0’ is 48 or 0x30.
Iterate ten times, incrementing the output register at each iteration.

If that works, try 16 characters from ‘A’ to ’P’.