backlight not working with lcd plug

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backlight not working with lcd plug

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dd180

For a small project I wanted to make use of the lcd plug. After assembling the plug and connecting it to a JeeNode, I uploaded the lcd plug demo and... it didn't really do anything.
I checked that the JeeNode and LCD work just fine. With an external power source I also checked the backlight was working as intended. Also my multimeter shows that there seems to be a signal coming into the board and I registered pulses on some of the pins. The soldering seems to be just fine, so I'm suspecting either I overlooked something trivial, did something really stupid or some part of the plug isn't working as it should. Did anyone have similar problems, or tips & ideas on how to find the culprit here?

Posted 18/02/2011 21:37:55
johno

I forgot the three solder links required on the PCB - I'm ashamed to say out loud.

Posted 18/02/2011 21:58:35
tankslappa

You need to decide if you want to control the backlight or not, and solder the jumper link to suit. Solder it to "I" and you can use PWM on the interrupt pin of the JeeNode ports to control the brightness. Connect it to "P" to have it powered from the "P" (unregulated) rail of the JeeNode.
If you don't solder it to either, it remains off.
If you solder it to "I" and don't implement the PWM it will remain off.
If you solder it to "P" and power your JeeNode from 3.3v direct to the 3.3v pin (and nothing to "P") it will remain off. Be wary of this one when using the AA Power board, there is a link on the AA power board you have to make to select if you want the converted 3.3v to be presented to the "P" pin, or the original source voltage (1.2-1.5v). If you don't make the choice and solder the link on the AA power board, the "P" rail will not have anything on it.
The link is labels SJ1. Connect left and middle together to connect the original power source to the "P" pin (you probably don't want this, 1.2-1.5v will be too little for the backlight). Connect right and middle together to supply the upconverted 3.3v to the "P" pin.

Posted 19/02/2011 01:58:08
dd180

Thanks for the speedy feedback guys, it looks like I overlooked this.. will try it out today!

Posted 19/02/2011 07:29:09
dd180

Indeed, I read the docs and completely forgot the power settings. It works like a dream now!

Posted 19/02/2011 08:07:32
johno

Hi tankslappa,
Are your pictures of the graphics board rather than the LCD plug?

Posted 19/02/2011 14:21:33
tankslappa

Oh blimee, you're right! I completely misread the question! I've been playing with the Graphics board so much recently that when I see "LCD" I think of the big graphical LCD panel, and not the 2x16 LCD panel which embarrassingly enough I use regularly (as a finished/working project) on my wireless camera flash trigger.
I'm glad you were here to give the correct answer!
I shall go sit in the corner until I learn to read!

Posted 19/02/2011 16:51:59
johno

Ha, you can make it all up by telling us if we control the back-light brightness on the lcd plug using PWM?

Posted 19/02/2011 17:06:20
tankslappa

Well with a bit of re-wiring I guess you could ;-)

Posted 19/02/2011 17:18:04
jcw

You could do software PWM to adjust the brightness on the LCD plug. It'll have some overhead, since the bit toggling needs to go through software I2C, but it should work fine.
Basic logic: after N1 millis, set backlight on, and N2 millis set it off, and repeat forever. Using a MilliTimer to do this in the background, i.e. called often in loop(). Where N1 is perhaps 1..15 and N2 could be 16 - N1.

Posted 19/02/2011 18:12:22