wkpizza
Newbie level 3
Blank display
If it's not a wiring problem, the main problem tends to be that the display contrast is not set correctly, or that they have used an extended temperature range display without realising that it needs a negative contrast voltage.” Steve Lawther from this page
Otherwise your backlight may be the problem.
Contrast
If you can sweep the contrast control pot from one end to the other and you don't see any change, (even if there is no text on the display, you should be able to see the pattern of pixels with the contrast full up or full down) And you are sure the wiring is correct, Then you -probably- have a display that needs a negative contrast voltage (between 0 and -5 volts, not 0 and +5 like the CORE gives). SmashTV Watch out for Vee pin. (Usually found in 'extended temperature range' displays)
How do I generate a negative voltage for the contrast?
This site shows a decent example of the easiest way to create a negative contrast voltage without a negative rail on your power supply. This works because the current draw/power requirement of the contrast supply is very very small, and there is a wide range of easy to use IC's besides the example given on the site for this. E-SHINE DISPLAY
Backlight
Does your LCD backlight flash once then go dark when you apply power to the core? If yes you probably have the “A” and “K” connections reversed, And this condition might be pulling several times the usual power requirement from the power supply. (IE regulator hot enough to burn it's number into your fingertip!) E-SHINE DISPLAY
If you have connected A and K right and your backlight is still flashing AND your regulator is very hot….then you can be sure that your power supply isn't strong enough for the whole box (especially if you have more than one display). Solution: Build a separate power supply for the backlight(s). Doc
Still not working? Maybe it's Electroluminescent (EL) type. Might need 'so called' inverter circuit to drive backlight.
If it's not a wiring problem, the main problem tends to be that the display contrast is not set correctly, or that they have used an extended temperature range display without realising that it needs a negative contrast voltage.” Steve Lawther from this page
Otherwise your backlight may be the problem.
Contrast
If you can sweep the contrast control pot from one end to the other and you don't see any change, (even if there is no text on the display, you should be able to see the pattern of pixels with the contrast full up or full down) And you are sure the wiring is correct, Then you -probably- have a display that needs a negative contrast voltage (between 0 and -5 volts, not 0 and +5 like the CORE gives). SmashTV Watch out for Vee pin. (Usually found in 'extended temperature range' displays)
How do I generate a negative voltage for the contrast?
This site shows a decent example of the easiest way to create a negative contrast voltage without a negative rail on your power supply. This works because the current draw/power requirement of the contrast supply is very very small, and there is a wide range of easy to use IC's besides the example given on the site for this. E-SHINE DISPLAY
Backlight
Does your LCD backlight flash once then go dark when you apply power to the core? If yes you probably have the “A” and “K” connections reversed, And this condition might be pulling several times the usual power requirement from the power supply. (IE regulator hot enough to burn it's number into your fingertip!) E-SHINE DISPLAY
If you have connected A and K right and your backlight is still flashing AND your regulator is very hot….then you can be sure that your power supply isn't strong enough for the whole box (especially if you have more than one display). Solution: Build a separate power supply for the backlight(s). Doc
Still not working? Maybe it's Electroluminescent (EL) type. Might need 'so called' inverter circuit to drive backlight.
