Display Backpack + Potentiometer Mount Problem

[MrAl]

Hello there,

I got my case today for the dual clock timer i am building. It's a small case, just big enough to hold the display and Nano and RTC board.

The problem is the display has a standard I2C backpack which allows the Nano to use just 2 pins (CLOCK and DATA) to communicate with the display.
Now that's great in itself, but the standard backpack has a pot on the back of the board to adjust the contrast, and that is great in itself too until you go to mount it in a case. The problem is that the pot is located to the left horizontally and about center vertically, so it makes it very difficult to mount anything behind the display like the Nano board because it will block access to the pot adjustment slot. That needs to be turned with a small screwdriver now and then to adjust contrast.

Removing the pot is only possible if the backpack board is removed, and to remove that requires quite a bit of difficult unsoldering of the header that mounts the backpack to the display board. So that is not really a good idea. The pot can be ground off with a Dremel, but that totally ruins it.

So the best bet seems to be to set the pot to the mid setting, then connect a new pot in parallel to the old pot. The old pot is probably the standard 10k used. The new pot may be a 5k unit.
Luckily the pin to the display adjust terminal is easy to access and solder to and so are the +5v and GND terminals.

Also thought about PWM combined with EEPROM stored up/down setting.

Any other ideas?

 

[Mike_2545]

I have used several LCD w/backpack and have only adjusted the contrast once on each unit(Just after assembling them). I don't know which modules you have but you may luck out and be in the same boat.

 

[MrAl]

Hi Mike,

That sounds interesting. I read that the contrast can change with temperature, but i never did any tests to find out exactly what range of temperatures it can handle without additional adjustment. I'll have to look into this idea more and do a couple tests, thanks.

 

[Nigel Goodwin]

That sounds interesting. I read that the contrast can change with temperature, but i never did any tests to find out exactly what range of temperatures it can handle without additional adjustment. I'll have to look into this idea more and do a couple tests, thanks.

It's unusual to see a customer adjustment for LCD contrast, most are simply set during manufacture.

 

[MrAl]

It's unusual to see a customer adjustment for LCD contrast, most are simply set during manufacture.

Hello,

That's interesting too, as virtually every backpack that i've ever seen for the 1602 or similar displays come with a small square blue pot on the back i think it is 10k. For the ones that dont come with a backpack, you can buy the backpack separately and it has the pot, and for those where you dont want a backpack they recommend connecting a 10k pot to the adjustment terminal, which BTW is there for adjusting the contrast

What i had read was that the display could change slightly and i had read that about other LCD's too so i assumed that the contrast might have to be adjusted now and then. If you dont mind seeing the slight 'grid' behind each digit though it may not matter to you. I read that they are temperature sensitive, but it could be that the difference is small so once set it stays set for a long time, provided nothing else changes anything like for example vibration or aging of one or more components.
The Wintek displays i have also have contrast adjust, but that is done in software by sending codes to the display, so no pot needed.

Come to think of it, i've never heard of a display without some kind of contrast adjustment and usually other adjustments too.

They sell the backpacks on Banggood and all they are really are serial to parallel converters with a contrast adjust pot also, os they could be used for other displays too or even other devices to save on uC I/O lines.

 

[be80be]

They all come with pots to set contrast But like what has been said you set it once and are done. I never had and problems with one needing changed after it was set.
Now that setting didn't work with every LCD I have one I use to test LCD's before I solder them to the backpack but the ones i left on a lcd worked great as long as it doesn't get really cold but then I just put it in my pocket and it worked fine I did have one get to cold to see.
But I found out fast you need to make sure they work before hand I got a box of blues ones and not all of them worked.

 

[Nigel Goodwin]

That's interesting too, as virtually every backpack that i've ever seen for the 1602 or similar displays come with a small square blue pot on the back i think it is 10k.

Sorry, I was talking about complete items, not just the LCD display 'component' - such a 'back pack' is still only a 'component' and not a complete unit.

As I said, it would be extremely rare to have the contrast pot available to the user in the final unit.

 

[MrAl]

Hello again,

Yes ok that makes more sense now

There is another 'angle' to this too though, and that is actually the angle of view. I noticed that if i adjust the contrast so that the background digit 'grid' just disappears (and you can see the digits like 1,2 3, clearly) if i tilt the display back just slightly so that i am viewing from an angle slightly below perfect horizontal, the grid becomes more and more visible with angle. It does not seem as bad rotating left and right though. So depending on the view angle a user may wish to adjust, at least with these 1602 and 2004 type displays.

I adjusted mine yesterday for a good contrast at a perfect horizontal view angle after we talked about this a little, so i'll see how long it stays set correctly at that same view angle. My indoor temperature doesnt change much though. so this may not be the best test. Probably a better test would be to take it outside on a cold day and see how much it changes (if at all) after a while. I probably wont need most things to work outside but maybe one or two things for the car might have to work in more extreme temperatures.
Also, for some LCD's temperature compensation is sometimes introduced in the form of a thermistor and maybe a few resistors or something. That would help eliminate the need to adjust any display if it was in fact temperature sensitive.
From what i had read it's the liquid crystal technology itself that can vary not the electronics, maybe due to the fluid temperature.

My Tablet does not need adjustment as far as i know. My PC monitor would be worthless without a contrast adjustment.

 

[MrAl]

Hello again,

Something interesting came up.

I had forgotten just how small the Nano is. It's only about 1.8 inches long by 0.7 inches wide and the highest point vertically is the top of the mini USB B connector which makes the max about 0.4 inches high. That means it may be able to lay flat on the bottom of the case which would mean it would not have to be mounted directly behind the display board. That of course means the pot may be accessible through a hole drilled in the back after all.

I went to start measuring for the case cutouts for the display and connectors and that is when i noticed that this may not be too hard to do after all. I just have to mount the display up a little higher vertically then originally planned in the case. I cant mount it off center as i really wanted to then because of the screw posts for the case cover mount, but in the center horizontally might look better anyway.

I'll have to see how this goes now. I'll leave the hole out for now anyway though so i can see how long it goes without needing an adjustment. The hole can always be drilled later. I'll post a pic when i get going with this so you guys can see what i was talking about.