HD44780 Module brightness problem

I got my LCD Module and a Display from ebay.
I soldered the pins on it to wire it.
But when i want to Write Text, the Display backlight is to shiny.
Its a negative Char Display. But i think its broken. I rewired it three Times. Always the Sams Problem.
Want can i do?


Looks like your contrast needs adjustment. But then I haven’t tried the module so I could be wrong. I did a quick search of the internet and it appears that with this display type you will need to connect pin 3 to ground possibly with a resister. I think that is what Vo is for.

Yep, looks like you just need to dim your backlight with a resistor.

I’m with dave on this one. You have to get the contrast set correctly. But i dont know how that module sets the display’s contrast.

Mh, i will test the resistor to reduce the current. But i also think i have to set the contrast. But dont know how…
Is there a way to send commands to the driver?

I tried to get the schgematic for that module but got a big Error 404…

[quote]Error 404

We’re sorry, but /downloads/Gadgeteer/Module/HD44780%20sch.pdf could not be found.[/quote]

From the picture of the module it looks like pin 3 of the display is shorted to ground via R2.

Do you have a datasheet for the display?

I suspect that you will have to replace R2 with some other value.

I checked the web and it looks like when you use a display with the HD44780 controller, contrast is controlled by the current on pin 3 of the display board. This is labeled Vo on the module.
On the module as shipped, the Pin labeled Vo is tied to ground through R2 and that is a 0 Ohm resister, basically a jumper. You will have to check with the display manufacturer to find how to calculate the correct value of resister you need to replace it with for your display.
The other option is to add to your existing circuit. You did not describe how you connected the module to the display, so let’s assume you soldered pins on the module and then soldered them to the display. In that case you will need to remove the pin entirely. Then add a poteniometer between the Vo and pin 3 of the display.
See the attached schematic

Removing a pin like that runs a very high risk of pulling out the through hole plating.

Rather remove R2, and connect the potentionmeter to where R2 was soldered…

@ GMod(Errol) - Oh yes I agree. My only reservation was that some people are unsure of themselves when dealing with surface mounts. But since Suplanus already said he had soldered and unsoldered already, I would say the risks are equal. The board could end up damaged both ways. Either in messing with the smd or with removing the pin.

I would say, if you are not sure about how to use one of these modules, it may be a good idea to ask the forum before doing any soldering :slight_smile:

Oh by the way. Yes the link is broken, but here is the link to the schematic pdf http://www.ghielectronics.com/downloads/Gadgeteer/Module/Display%20HD44780%20sch.pdf

The description of the module, http://www.ghielectronics.com/catalog/product/358 , does discuss the very issue GMod and I have been talking about. I guess I should follow my own advice and check the documentation before making any mods to the a module.

thanks for the replies.

Here is the documentation of the display:

Yep, they just say you need a potentiometer that adjusts between 0K and 20K.

Yep, and there is your answer right in the middle of the page. Vo through a 0-20k potentiometer to VSS. So connect a 20k pot between pinj 3 on the display and Vo on the module or replace R2 with a 20k pot. Then you can adjust the contrast to whatever level you want.

@ Suplanus - Have you tried the potentiometer yet. I notice your comment on my Codeshare submission which lead me to believe this has not worked for you. Let us know what you find.

I have no poti yet. I will try it and Post the result.

I found a 10kOhm poti… and it works :slight_smile:

Big thanks for the help!

Great work. Now have some real fun.

Bonus for adding some details and images on wiki page of the display breakout page