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Topic: GLCD Help with contrast pot (Read 1 time) previous topic - next topic

crimeplanner

I have an Agena AG1286401 LCD display, which I can't seem to get the contrast circuit working properly on. According to the GLCD docs, it is a "Panel B" configuration. I have wired pin 1 (Vss) to the first pin of my 10k pot, pin 3 (Vo) to the wiper and pin 18 (Vout) to the third pin. The display does not show anything, though the GLCD diagnosic sketch passes. I also tried using the contrast diagrams in the datasheets included below, but they didn't seem to work either. I'm using an Arduino Uno R3.

floresta

Quote
I also tried using the contrast diagrams in the datasheets included below, but they didn't seem to work either.

The connections in your description should allow you to adjust the contrast voltage between 0v and -18v (assuming that Vee is -18 v).  Since many GLCDs require about -4 v this seems to be a good choice.  Can you measure the voltage between pin 3 and GND to see if this is actually happening?

The connections shown in your first link should allow you to adjust the contrast voltage between +5v and -18v.  If your display happens to require a positive voltage on pin 3 this would be the one to use.  It should also work for displays requiring a negative voltage, but with a coarser adjustment.

The connections shown in your second link are incorrect.  You would use a second battery or a negative voltage from pin 18, not both.

I couldn't find any information concerning the contrast connections in your third link.  It does show minimum and maximum values for the LCD drive voltage which are obviously inconsistent.


Don

crimeplanner

Hi there- my multimeter has gone bust so I can't measure anything for now. I was thinking it may be the pot, or even me blowing it by accident...    :~  here is the pot i'm using https://www.sparkfun.com/products/9806

bperrybap

Is your backlight working?
If you have a display with light pixels on a dark background you will not see any pixels
until the backlight is working.

--- bill

crimeplanner

I do not have a 220 ohm resistor to run the backlight property, as it is rated at 4.2v max, while the Arduino is at 5v. However, I tried running it on the Arduino 5v supply and it went, but I could not see any pixels. I know if the display is "ready" but not displaying anything there would be a black shade if the backlight is on, however I can't see the shade.

Maybe the power IC is fried, or the pot I'm using isn't working properly. Either way, I will probably end up buying a new one if all else fails, as they were going for cheap. For me it's not worth it replacing the power IC/display module anyway.

bperrybap

I don't understand what you saying.
Are you saying you have a display with dark pixels or light pixels?
i.e. what should the colors of your display be if it were working?
black pixels on yellow/green background, white pixels on blue background etc....

If you have a display with white pixels you will not see any pixels until you
get the backlight working.

Also, on a display with light pixels on a dark background, depending on the constrast
voltage going into Vo you may see a dark area on the lit background where the pixels are,
you may see an area of entirely white pixels or you may see nothing.
It depends on the contrast setting.

No sense in buying another display until you figure out what is going on
with the one you have.

If the backlight needs a resistor (some do some don't) and you don't use one,
the backlight can be fried and then you won't be able to see any pixels
on a display that has a dark background and light pixels.
Some require very small resistors like 4-10 ohms some require bigger like 100-200 ohms.
To figure it out, you will need an ammeter (most DMMs can do this) to tell how much
current the backlight is drawing.
You will to measure the current and use a resistor to set it below what the datasheet says.

If the Vee signal (pin 18) is ever accidentally hooked up incorrectly to ground or power
the negative power supply can be fried. If so, no pixels will ever show up.
You need to test it with a volt meter to know if it is working.

--- bill



crimeplanner

The display is black pixels on a green backlight. I don't think the backlight needs to be powered for the pixels to be seen, as I have seen similar displays working without the backlight.

bperrybap


The display is black pixels on a green backlight. I don't think the backlight needs to be powered for the pixels to be seen, as I have seen similar displays working without the backlight.

That is correct. The backlight will not be necessary to see pixels on that type of display.
Everything else sounds ok.
Was the display ever miswired?

You will need a meter to check the Vout/Vee voltage to see if it is working properly.

--- bill



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