zwitter said:
I ordered this ebay item 271061312409 and another like 121189232611.
They mostly use the same chip so text should be ok. May need to check the backlight connections and adjust the brightness pot or maybe the resistors connected to the adjustment pot. Many of us can assist with that or probably even help with the solution if you can present the problem with details.
James
Zwitter
Sent from my iPad using Tapatalk HD
Hi James,
Thanks for your feedback.
I've been trying to figure out which components need to be modified to adjust the LCD backlight brightness, which I think is controlled by pins 15 & 16 - I figure R6 120ohm resistor is the likely candidate, can anyone confirm this?
These are the comparison photos showing the difference in brightness between the 16x2 screen that I got with my kit and the 20x4 screen that I ordered from Modtronix_au on ebay:
https://www.dropbox.com/s/prten9b4wqxn4ds/Photo%2011-06-2014%2023%2026%2011.jpg
https://www.dropbox.com/s/vicdv6j3frizqrf/photo%202.JPG
As you can see the 16x2 screen worked perfectly while the 20x4 backlight is quite dim.
The operating parameters for Voltage & current obtained from the 16x2 and 20x4 data sheets (see attached) do vary quite a bit between each screen, eg:
16x2 voltage range 3.3-3.7V
16x2 current range 28-40 mA @ 3.4v
(I measured the voltage on the shield across pins 15 & 16 at 3.74v, haven't figured how to measure the current but I'm assuming its within the range listed)
https://www.dropbox.com/s/q5fwq23164t1cjt/Photo%2011-07-2014%2008%2013%2052.png
20x4 voltage range 4-4.4V
20x4 current range 224-420 mA @ 4.2v
https://www.dropbox.com/s/1te5y5pn3qyd8qg/Photo%2011-07-2014%2008%2008%2007.png
The big difference in current might explain why the pot needs to be adjusted to the limit to get the text to display, otherwise there is no text visible, and at no point does the contrast turn the whole screen black like it did with the 16x2 screen.
Would I be right in saying that the voltage controls the brightness of the backlight?
i.e. 3.74V gives perfect backlight brightness for 16x2, but would be below the ideal range for the 20x4.
And I assume that the pot adjusts the current through pins 15&16?
Any further feedback would be much appreciated guys,
Thanks,
Brendan.
Message edited to add photos and complete the text.