Mpguino display "pulsing"

[frank316]

Hey guys I am working on making an mpguino. I used an arduino uno and an lcd and everything seems to be working with it wired up on my breadboard, all the buttons work, menus etc. I have tried a bunch of different versions of the code, all seem to have the same problem. On the set up screens with contrast and all that the screen works fine, but as soon as you go to any of the actual display menus the backlight stays on but the text fades to almost nothing and then comes back on, fairly rapidly i'd say once a second or quicker. I'm don't know much about code or programming so not really sure if its something i'm doing or what the deal is. Anyone have any insight? Thanks guys

Ben

[Nevyn]

I think others have found issues with breadboarding - too much stray inductance or something similar, IIRC.

[bobski]

Originally Posted by Nevyn

too much stray inductance or something similar, IIRC.

Seriously? :/

Get a 3-lead 10K-ohm potentiometer. The little trimmer types should work fine. Wire one end to 5V power, the other to ground and connect the wiper to the contrast pin of the display. If you're not sure which leads are the "ends" and which is the wiper, measure the resistance between two of the leads with a multimeter. If the resistance changes when you adjust the pot, you've got an end and the wiper. Try different combinations until you find one that doesn't change (it should read about 10K-ohms).
Once you have the pot hooked up, start up the MPGuino so it's displaying some text and adjust the potentiometer to your desired contrast level.

[dcb]

The mpguino uses pwm for contrast control bobski, to keep the component count down, and thus improve the chances of getting it right, it sounds like the contrast part is working.

Frank, something might be miswired or there may be a problem with the LCD, the half screen of blocks is a common symptom of a loose or bad connection. Maybe all the button pressing is aggrivating an existing bad connection?

[bobski]

Originally Posted by dcb

The mpguino uses pwm for contrast control bobski, to keep the component count down

Yes, I am fully aware of that. I can and have read the diagram.
Slow pulsing of the contrast suggests that either the duty cycle the MPGuino code is outputting is varying (you're on your own there) or the PWM signal isn't compatible with the model of LCD being used. Since the signal isn't a true analog voltage (as a potentiometer would produce) but a square wave, perhaps the frequency of the wave conflicts with some internal timing of the display hardware. Unfortunately, that doesn't explain why the display works fine on the contrast adjustment screen but not elsewhere. That detail alone suggests a software bug.
Try the potentiometer setup to make sure it isn't a problem with the display module. Once you're sure the display is working as designed, work on the MPGuino.

[frank316]

wow.. I feel like an idiot.. I checked the wiring like the 3 times, Everything was wired fine, but for some reason i swore the lcd screen needed 3.3v and not 5v.. I was wrong, works fine now. Working on soldering it together and putting it in an enclosure now. Thanks for the help and ideas guys..

[bobski]

Originally Posted by frank316

for some reason i swore the lcd screen needed 3.3v and not 5v

Some do, but generally not the type used with the MPGuino. I've been looking at graphic LCDs for a possible next version of MPGshield... It seems many of Electronic Assembly's graphic displays (which can be controlled via 4-wire serial IIRC) run on 3.3V.