Second LCD to fail

computer guy · 2010-01-16 13:09

I recently purchased a 4x20 Backlit LCD display from Parallax.
After I opened it up, I configured it for "test" mode and wired it up like so

LCD          Proto Board
5V----------+5V
GND--------VSS

Imediately random pixels where lit up or half lit up (dim).
I posted on the forum and the general consensus was that the LCD was DOA (dead on arrival).
I emailed Parallax and they sent me a new one under warranty. Thank you Parallax

I wired up the new one and it worked great.
I then wired up the rx pin to p0 on the proto board, set the LCD to 19,2000 baud and started to write code.
I have been using it for about a week or so now with no problems however I turned it on today and the backlight is not comming on and the entire 1st and 3rd rows are lit.
Thinking it was a problem with my code I put the LCD into test mode and the same thing happened. No backlight with 1st and 3rd rows lit.

I have tested the output of the 5v regulator on the proto board with a multimeter and it is at a steady 5v.

Can anyone help me with this? I don't think Parallax will tolerate another warranty request even though I have connected it as per the documentation.

Thank you

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Unknown · 2010-01-16 15:50

I don't know the answer to this one but I would try using a resistor and running one under specs.

kf4ixm · 2010-01-16 15:57

maybe try a lower baud rate, i have the same lcd and i have found that i get better results running at 9600. seems like i got errors sometimes whenever i used the higher rate, maybe im in a high noise enviroment or such, but whenever i started getting random characters and such, changing back to 9600 eliminated the problems.

computer guy · 2010-01-16 22:05

Thank you both however it is doing this as soon at it gets power (no data sent to it) and also in "test mode", where it is meant to display "
Parallax Inc.
www.parallax.com

Thank you

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James Long · 2010-01-16 22:52

computer guy said...
Thank you both however it is doing this as soon at it gets power (no data sent to it) and also in "test mode", where it is meant to display "
Parallax Inc.
www.parallax.com

Thank you

This sounds like you may be possibly over writing some value in the controller chip. Although unlikely, it is the only thing that would cause two displays to fail in that short of tome.

The only other thing I know of would be reversing the power.

I can't think of anything else, unless it is an over power issue.

James L

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James L
Partner/Designer
Lil Brother SMT Assembly Services

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computer guy · 2010-01-16 23:21

I have checked the voltage on regulator and it's 5V.
Checked polarity and it's correct.

One thing I forgot to mention is that the proto board was being powered from a 9V battery and it went flat whilst writing to the display.
Maybe something in the controller chip became scrambled.

P.S. The first display was dead on arrival. This is the first display to actually fail after using it.

Parallax?

Thank you

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James Long · 2010-01-16 23:29

computer guy said...
I have checked the voltage on regulator and it's 5V.
Checked polarity and it's correct.

One thing I forgot to mention is that the proto board was being powered from a 9V battery and it went flat whilst writing to the display.
Maybe something in the controller chip became scrambled.

P.S. The first display was dead on arrival. This is the first display to actually fail after using it.

Parallax?

Thank you

I have a few questions, that may or may not be pertinent. How do you power up the system with the display on it? Do you have other things on this regulator? Is the display powered with nothing else attached? What is the minimum amount of draw the regulator needs to be active?

I'm wondering if you got a "spike".

James L

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James L
Partner/Designer
Lil Brother SMT Assembly Services

Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos!

computer guy · 2010-01-16 23:32

The 5V regulator is powering the LCD display only.
The 3.3V regulator is powering the propeller chip and related circuitry (crystal, EEPROM, etc) and a RTC chip I purchased from Parallax.

To power it on, I flick the power switch to possition 1.

Thank you

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Patrick T · 2010-01-16 23:34

If the first and third lines are lit it sounds like it has not been properly initialized. Not sure why that would be since the SX on the back handles all of that. - Patrick

computer guy · 2010-01-16 23:52

@Patrick,

I think the memory on the SX has become scrambled due to the power loss from the 9V battery going flat.
Maybe Parallax needs to add a brownout detector to the LCD board.

I managed to find a 7.2V DC power supply and I will use that from now on (unless we have a blackout).

Thank you

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Post Edited (computer guy) : 1/17/2010 12:11:24 AM GMT

James Long · 2010-01-17 00:24

computer guy said...
@Patrick,

I think the memory on the SX has become scrambled due to the power loss from the 9V battery going flat.
Maybe Parallax needs to add a brownout detector to the LCD board.

I managed to find a 7.2V DC power supply and I will use that from now on (unless we have a blackout).

Thank you

I do not think this is a power loss problem. I haven't ever had a LCD go down while communicating with it, but I'm sure the issue would have come up before if that is the case.

James L

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James L
Partner/Designer
Lil Brother SMT Assembly Services

Are you addicted to technology or Micro-controllers..... then checkout the forums at Savage Circuits. Learn to build your own Gizmos!

computer guy · 2010-01-17 00:36

I need to continue working on my project as it is for my HSC and this is preventing me from proceeding.
Power loss is the only thing I can think of, other than a faulty SX chip.

It's 4:30PM on a Saturday so Parallax can't help at the moment and I really need this working.

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Chris Savage · 2010-01-19 19:51

By any chance your MCU isn't powered up before the LCD is it?

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Chris Savage

Parallax Engineering
Check out the new Savage Circuits TV!
·

computer guy · 2010-01-19 21:55

Because they both run off the same board, no. Why do you ask Chris?

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Chris Savage · 2010-01-19 23:30

I was trying to determine the possibility of latch-up often caused by the I/O pins on the SX having voltage on them before the chip is powered up. That appears to not be the case, however.

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Parallax Engineering
Check out the new Savage Circuits TV!
·

mikediv · 2010-01-20 00:45

Just a thought I was using a wall wart and while it had a steady 12 volts on my multi meter when I looked at it with my scope is was almost a sine wave AC it caused me all sorts of grief until I figured it out

computer guy · 2010-01-20 02:35

I have changed to a regulated 7.4V DC power source. Hopefuly this will stop any future problems.
Maybe it was a spike.

Thank you all for your suggestions.

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Paul Sr. · 2010-01-20 13:56

Just a thought - do you have the GROUNDS from both supplies tied together?

computer guy · 2010-01-21 06:33

It's the Parallax Inc. Proto Board (from their website) and both the 5V and 3.3V regulators share the same GND plane.
Thanks for your input though Paul.

Have a new one on the way. Fingers crossed

Now that I have a more reliable power source and a third LCD hopefuly it won't happen again.
This is a first for me and hopefuly a last.

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Second LCD to fail

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