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Topic: [SOLVED] 20x4 Winstar LCD empty (Read 4384 times) previous topic - next topic


POSITIVE gives me possibility to control backlight with sketch /lcd.backlight(), lcd.noBacklight()/.

Either one gives you the ability to control the backlight as the polarity only affects
the correctness of the backlight control not the control itself.
When the polarity is reversed from what it should be,
backlight() will turn off the backlight and noBacklight() will turn on the backlight.
Perhaps you mean:
POSITIVE gives you the ability to correctly control the backlight as intended.

When using the i2cLCDguesser sketch, you want to use the first guess of
parameters that pass the test. And by "pass" it means the first one
that shows up on the display with the backlight on.

Was there any kind of label, vendor, or manufacturer name on that backpack?
I'd like to add to my list of known backpacks.

--- bill


OK, now I got it :)
Bill, thanks a million for your patience and commitment.

Re backpack - there was nothing more than on the photo (my 1st post). But on my vendor's website (link attached, in polish but pictures are universal ;)) there are more pictures which might lead you to YwRobot. But this is just a speculation ).




All the tiny details really matter with stuff like this.
While pictures are universal, the picture you posted in your first post is not the same board as either of
two boards, in the link you posted above.
Which board do you have?

--- bill


This is the board from the 1st post (picture attached) - no name.


I wonder if the contrast pot is OK as the adjustment in quite limited i.e. very narrow, in the beginning of scale.

Absolutely.  The contrast itself is the actual voltage between "Vo" - pin 3, and the +5V rail.  The 2k2 resistor chain R1 to R5 divides this up into a set of steps which are used to multiplex the LCD display which is very sensitive to the voltage - that is actually how the multiplexing works, only segments which are strobed with a combination equal to the full 4.5 volts will actually show.

So I say 4.5 volts - this corresponds to about 0.5V on the Vo terminal, so the potentiometer is always set near to ground - setting it midway selects 2.5V which produces no contrast at all.  In fact, a fair approximation to the correct voltage is a 10k resistor to Vcc and a 470 ohm to 1k resistor to ground.  Just a 1k to 2k resistor to ground will probably work (since the internal divider already totals 11k).  If fine control of the contrast was needed, the potentiometer would be a 1k in series with a 8k2 to Vcc, but in practice, this is nowhere near that critical and once set, it generally does not matter if the potentiometer is obscured by mounting the display (as happens with some versions of the "backpack").

Now a matter of interest - there is a 3.3V version of the display.  You will note a mounting pad "U3" on the board and three jumpers of which "J1" is soldered as well as capacitors C1 and C2 (it is by the way, always a good idea to mount a 0.1µF capacitor across pins 1 and 2).  On the 3.3V module, these components comprise a "charge pump" which actually generates a 5V supply from the 3.3V, a different jumper (or two) is soldered and the internal Vcc is now 5V.

Some variants of these displays ("extended temperature") require even more voltage to drive the LCD, and so require an actual negative supply for Vo which may or may not be supplied by the module.

And by the same token, you will note that if your 5V supply "sags" excessively, the LCD will begin to fade as a result.

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