Em 25/04/2014 17:15, Peter Johansson escreveu: > On Thu, Apr 24, 2014 at 6:59 PM, IVP wrote: > >> I think the only time I ever fitted a trimpot, as per the datasheet, >> was the first time I used an HD44780-type alphanumeric. Then >> realised how ridiculous a waste it was. Now I either tie Vo to >> 0V or, for best contrast, a 47R/4k7 divider to raise Vo to just >> above 0V > I strongly recommend against this, *particularly* if you are using a > HD44780 for the first time. > > The range where the display is visible rather narrow and varies quite > a bit from module to module. If you do not have the proper settings > the display won't be visible. > > I got doubly burned because the timing on the first module I played > with was at the edge of spec and the initialization routines on all > the libraries I played with failed to initialize it properly. > > Even when it did initialize properly, I didn't know because the > display still wasn't visible. The trick here is to adjust the contrast to a point that the background starts to darken, but just a little. This way it is guaranteed that when the LCD shows some text it will be readable. If the display is not initialized then the first line will be full of black squares (that is, all pixels on). If you adjust the contrast so the squares are visible but not too dark, then again, when the display gets initialized and shows text it will be readable. Isaac --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .