Matrix Orbital Corp

I am using GLK24064-25 (PCB rev. 1.3) and are experiencing problems where the display will completely lockup, with the contrast being off (usually the display is extremely dark), and a power cycle is required to restore the device to a usable state.

I am commanding the LCD using serial communications (RS232) at a baud rate of 19200 with no hardware flow control configured on the serial port (obviously). I also am not using the software flow control provided by the LCD.

I basically just use the LCD in text mode, setting a position and then writing a string to the serial device. Usually these strings are short, formatted numbers. Occaisionally they are labels or a line of text.

What could cause the behavior that I am seeing? It is not consistant, as far as I can tell. The lockup will sometimes occur in 30 minutes, and sometimes not for over 30 days. To reproduce it in the lab is incredibly difficult. I have only seen it occur in the field.

Any insight would be appreciated.

Thanks,

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Ryan J. Allen

Hi rallen,

Thank you for posting at the forum.

What I can usually tell from random behaviour is noise can be an issue. How are you enclosing the display? Are you also grounding the unit commonly with your system?

Tom, thanks for your reply.

Currently we have the ground floating. We used to ground the LCD with the digital ground on our control logic circuit board but stopped when we noticed more problems.

The LCD is mounted on our our chasis with nylon washers between the LCD and our chasis. The LCD itself is enclosed in the same area as our control logic circuit board (plus computer) in a 75cm x 50cm x 25cm area, but is not independently enclosed.

Thanks again,

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Ryan J. Allen

Ryan,

What kind of problems would you get from grounding the LCD with the digital ground on your control logic circuit board?

When the LCD was grounded to our board's ground we noticed bytes being stored in the keypad buffer, making it appear as if someone had been pressing keys. Out software, of course, could not differentiate between legitimate and "noise generated" characters.

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Ryan J. Allen

Ryan,

Is your control logic board connected to your earth ground?

I am sorry for taking so long to reply. I have been away for a few days.

Yes, our circuit's ground is connected to earth ground. I cannot say for certain that this was always the case (refering to the previously mentioned problem), but I can say that it is now.

Thanks again,

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Ryan J. Allen

Can you try grounding everything together, and let me know if you get the same problem as previously discussed?