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Old 01-02-2009, 11:21 PM   #1 (permalink)
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No display on MPGuino LCD, just backlight

Quick history: I got my MPGuino assembled, and had to change the 7805 voltage regulator.

Sometime during the process of desoldering the LCD and resoldering I must have messed something up...

With the new 7805 the gauge worked, however I had intermittent freezes... Not constant just 1 per trip whereever I was going...

Well, the last time I used it the screen went blank. I had a backlight so I knew power was still getting to it.

I hooked it up to my computer and still the same thing - backlight, but no characters at all.

I touched the LCD and I saw the normal display, moved it and it went away.

So, I had placed a spacer in between my 2 boards, so I took it out. and the display stayed. Unless I moved the LCD a little.

My next step was to desolder the LCD again - and snug it onto the header, and re solder. Well, I couldn't separate the board, but I had all the solder off of it... I resoldered, and now I all I have is a backlight display with no characters....

I checked continuity between all 16 pins on both sides of the board, and it was good...

I ohm checked all 16 pins through both sides of the board. All read good.. 0.00 ohms.

So, I'm at a loss. It was working before I de and re soldered. It's like a line or pin broke which delivers the info to the LCD, but all the pins check good... Any suggestions would be welcome...

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Old 01-03-2009, 10:37 PM   #2 (permalink)
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Ive had the backlit screen with nothing on it, but that always meant the chip lost the program. And that was happening from low voltage problems, or from touching the wrong part of the board with sweaty fingers. You could always try reflashing the program just to make sure it is there.

If it still doesnt work, it does sound like a connection problem. Maybe one little piece of solder that is bridging two pins.
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Old 01-03-2009, 11:29 PM   #3 (permalink)
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I know this might sound silly, but is there a link to idiot proof re flashing instructions?

Did you mean re flash the sketch? or re load the boot loader, both of which I'm trying to figure out...

I downloaded the Arduino v 0012 Alpha and copied the sketch off of the link from spiffie's website, and verified the sketch but it said the sketch was too big... So, I'm digging and digging for more info - anything that can save me some time would be great

*oops* just read the top of the sketch and saw that I'm suppose to be using Arduino v 0011...


** Alrighty** I downloaded v 0011 and I uploaded the current sketch... No change..

I am able to change the brightness on the screen, just still nothing but the backlight... and the backlight does time out after the preset amount of time... whatever it was before... So... I guess I'm going to desolder the LCD again and do some examining..
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Old 01-04-2009, 12:02 AM   #4 (permalink)
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I meant reflash the sketch.

dcb showed me once how to do the bootloader and make a cable when mine was acting up, but I didnt need to do it. Even he said that doing the bootloader took "a cable and some patience". So I would only try the bootloader as an absolute last resort.

Another thing I found is that you (or at least I) can only have one file in the computer with the pde extension, and I keep it called mpguino.pde. I normally keep one saved with the default settings for each vehicle. I have to give these others a txt extension, or it will give an error and not load the sketch.

Yes the wrong version of Arduino will cause problems. I would deal with that first.
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Old 01-04-2009, 12:49 AM   #5 (permalink)
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Well, I think I figured out the problem. Possibly.

I'm going to share my screw up with everyone because I learned a valuable lesson, and I'm pretty sure this is the source of my problem.

The first and second time I desoldered my LCD I used a common screw driver to pry apart the boards, because I didn't desolder them correctly.

And when I did that prying I put divets in the board...

Now, I didn't know that the signal line from the atmega runs along the outside of the board so I didn't know my screw driver was going to cause any real damage besides superficial...

So, here's a picture of the damage... For anyone who doesn't know - DO NOT use a screw driver to pry apart circuit cards!

For everyone else, - please feel free to laugh

So, now I guess a fix would be to solder in jumper wires to send the signals over to bypass the damage I did... Time to study the schematics I suppose..
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Old 01-04-2009, 01:47 AM   #6 (permalink)
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I checked continuity between Pin 13 and the small ring by the 2 pins that it looks like that signal goes through, and I had good continuity, so my guess that the divets I made in that line was wrong...

So, I soldered the LCD back to the board, and still no change...

I did re flash the sketch before-hand with no change...

So here I am, no idea where to go next. Besides desoldering the LCD again and investigating some more...
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Old 01-04-2009, 12:56 PM   #7 (permalink)
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I was wondering if anyone could tell me the pins on the atmega that deliver the digital display data to the LCD header?


I understand that Pin 1, 5, and 16 are ground on the header for the LCD.

I need to know the digital data Pins on the atmega to the header so I can solder in jumper wires in case I did damage the board.

I know my MPGuino still has functionality, because I can still adjust the brightness on the LCD and if I push buttons randomly it seems like I'm changing settings, because I push buttons and I can't change the brightness until I replug power to it.

So - my theory is - it still has the program on it, all connections are good except digital display data going to the LCD.

If anyone can point me in the right direction as far as getting the right pin or pins to jumper to the right header pins I should be able to get fixed. Thanks!
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Old 01-04-2009, 02:10 PM   #8 (permalink)
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here is the arduino based mpguino schematic:


and here is the actual chip pin mappings:


so you should be able to determine what pins on the atmega should be connected to what leads and which ones they shouldn't be connected to with that info and lots of probing with a voltage meter.
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Old 01-04-2009, 02:37 PM   #9 (permalink)
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Thanks Dcb! I saw the schematic, but not the pin mapping for the atmega. I appreciate it!
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Old 01-04-2009, 06:17 PM   #10 (permalink)
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I've done continuity checks and ohms checks between the atmega pins and the LCD and they all check good as well.

Could it be that I hosed up the atmega?

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