LCD or trimpot toast? --HD44780 & Sanguino

HW: Sanguino 1.0, LCD- 16x2 HD44780 compat.
SW: Tried default LiquidCrystal sketches and LCD4Bit
Problem: LCD just shows that it is powered, but doesn’t perform anything.

My setup:
P1 10k trimpot > GND
P2 10k trimpot > 5V
P3 10k trimpot
P4 RS > Sanguino P12
P6 E > Sanguino P11
P11-P14 Sanguino P5~2
P15 120Ohm Res > 5V

// include the library code:
#include <LiquidCrystal.h>

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

void setup() {
  // set up the LCD's number of rows and columns: 
  lcd.begin(16, 2);
  // Print a message to the LCD.
  lcd.print("hello, world!");

void loop() {
  // set the cursor to column 0, line 1
  // (note: line 1 is the second row, since counting begins with 0):
  lcd.setCursor(0, 1);
  // print the number of seconds since reset:

Any thoughts before I get a new 10k trimpot and LCD? :slight_smile:


What happens when you turn the pot?

Take another picture with the wires separated so we can see which one goes where.


Don, It goes blank and then shows what you see in the picture (fully lit). What is weird, I swear when I first got the trimpot that it stopped in each direction after so many turns, now it doesn't. I could be incorrect, but I really thought that. It can go as many turns in each direction. After so many degrees it is fully lit, the blank, then fully lit, etc. forever.

Thank you, -d

how is the trimpot wired, I dont understand

Right now it seems like you have it wired as a rheostat, but that does not compute

Here is how the trimpot is wired:

It goes blank and then shows what you see in the picture (fully lit).

This is correct. Back it off from “what you see in the picture” until that top row of boxes is just visible. The pot may not be quite “as good as new” but it is functioning satisfactorily since you won’t have to adjust it again.

LCD pin 5 (R/W) must be grounded. The examples mention that it ‘isn’t used’ but they are referring to the fact that the program doesn’t use R/W.

If that’s ok then it is time for a new photo as I mentioned before.


Here are the detailed pictures and yes, RW is grounded (P5 of LCD).

Those pictures are nice and clear, but in a little too tight. We have to be able to see both ends of each the six wires that interconnect the LCD with the Sanguino and we have to be able to distinguish between the wires as they make their way between the two devices.

I also suggest that you trim the wires so that the bare portion is only 1/4" long.

Another thought - recheck the four LCD data pins (LCD pins 11, 12, 13, and 14). You have specified them backwards from the example program. There's nothing wrong with this as long as you connect them as you have specified.

You have specified: LiquidCrystal lcd(12, 11, 2, 3, 4, 5); The generic form is: LiquidCrystal lcd(RS, E, D4, D5, D6, D7);

This means that your D4 must go to Digital Pin 2, D5 to Digital 3, etc.


Shortened wires and re-trimmed (1 wire I forgot to fully insert in one pic). Tried 11-14 on the LCD (2-5 on Sanguino) both ways -- 5-2 and 2-5. Same results. This is driving me insane, working on a much bigger project yesterday and everything was fine! Thank you for your help.

Updated pics:

Wait, why the heck is my red LED on my board blown. I literally just saw it in my pic, then looked at my board. Short? Could that be messing this up?

REPLACED LED - no difference.

I guess it is time to remove all the wires and reconnect them, one at a time, in a nice neat orderly way so that we can check your wiring. It really helps to have someone else check your connections but this can't be done when all of the wires are the same color and are also twisted together.

Also, we need a [u]single picture[/u] that shows both ends of each wire, so you can't get the camera (or Blackberry) in too close.

According to the schematic the red (debug) LED on the Sanquino is connected to PB0, which in Arduinoese is Digital pin 8. It won't light up unless you tell it to with a digitalWrite() instruction.


Agreed, I had already done that once (you can see my other post in the Syntax/Programs section). I was exhibiting this, tore my whole thing apart and put in just the LCD to isolate the issue. The issue is still occurring. Think I may try to get another LCD to verify it isn’t the LCD. After de-soldering and re-soldering the pins, it may have crossed something that I cannot see easily.

Think I may try to get another LCD....

While you are at it order some male header pins. Solder them to your LCD (instead of soldering wires to the LCD) and you will be able to plug it into your breadboard. You might also consider getting some more wire (not red).


Funny you mention that -- I had headers and removed them because of this issue - thinking something was touching. I do need more wire, yes, r-shack was out when I went by yesterday. Update later today I hope--this is just crazy.

Soldered male header pins back on. Now my LCD shows no signs of power. What pins (at minimum) are needed for it to at least get power?

Take a look at pins 18 and 19 of your Sanguino. Then examine everything else, including your newly soldered header, and make sure it doesn't look like that.


When the LCD was functioning, it produced red characters and the light on the right-side was also powered red. Now when powered it shows a backlit top row that is a blue-ish color and a bottom row that is a white-ish blend. Still does not work.

Detailed pictures:

I toasted the LCD, a new one worked like a charm! Thanks everyone for your help. :)