LCD issues with 3 or more shields stacked.

The LCD and Keypad Shield gives you a handy 16-character by 2-line display, 5 buttons and a controllable backlight.
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AussieMike
Posts: 3
Joined: Wed Apr 08, 2020 12:00 am

LCD issues with 3 or more shields stacked.

Post by AussieMike » Wed Apr 08, 2020 2:07 am

Hi All,

I'm having a problem with the freetronics LCD display when 3 or more shields are stacked. To explain the system stack I have.

TOTAL STACK: ( Eleven --> N Drive Shield (D10 used) --> Protoboard (5v, GND, A1 Input ) --> LCD+Keypad )

When I have any 1 shield + LCD shield combination ( Eleven --> shield (either n-Drive or Prototype) --> LCD+Keypad ) the LCD works great.

As soon as I add the extra shield into the stack the LCD displays all black squares, like the contrast is saturated. Importantly the
backlight and keypad is still working fine.

Things I've tried:

- Powered from 5v USB input.
1 shield + LCD Shield = 4.88v (Measured on the 5v pin LCD shield)
2 shields + LCD shield = 4.88v

- Powered from external 12v regulated power pack via DC jack.
1 shield + LCD Shield = 4.90v (Measured on the 5v pin LCD shield)
2 shields + LCD shield = 4.90v

- Reduced the LCD backlight to low level to reduce current draw.
- Disabled shield ports via software ( D10, A1, etc..) to check for incompatibility.

I have tested my proto circuit (on shield) thoroughly and am confident that it is working correct and causes no undue current draw.
Additionally the LCD works when it is stacked with only the proto.

When using the external power pack, the eleven on-board regulator does not get hot, it only feels slightly warm

I haven't yet explored adding a POT to adjust the LCD contrast, currently just the Eleven default. This seems the next step, but I wanted to see if anyone has encounter and solved a similar issue.

Thanks,
Mike.

Brissieboy
Posts: 206
Joined: Fri Sep 20, 2013 7:25 am

Re: LCD issues with 3 or more shields stacked.

Post by Brissieboy » Wed Apr 08, 2020 4:11 am

Welcome AussieMike.
You have several conflicts digital on pin usage with that stack.
The N Drive uses 3, 5, 6, 9, 10, 11.
The LCD uses 4, 5, 6, 7, 8, 9 as well as A0 for the key input.
You will need to modify one of them or change the setup in some other way such as using jumpers instead of piggy-backing.

AussieMike
Posts: 3
Joined: Wed Apr 08, 2020 12:00 am

Re: LCD issues with 3 or more shields stacked.

Post by AussieMike » Wed Apr 08, 2020 4:38 am

Hi Brissieboy,

Thanks for your reply, appreciate your input. I had considered this as an issue because I can see the active LCD data on the LEDs of the N drive board.

The thing that threw me is everything works perfectly (including LCD) when it's just the Eleven --> N Drive --> Keypad stacked.

Then I add another shield (with nothing on those LCD pins ) and the problem, occurs. When this issue occurs I still seeing all the same LED active on the Ndrive pins but a black squared LCD.

I assumed the inputs of the unused N drivers are relatively high impedence and shouldn't affect the LCD signals greatly, possible there an affect and adding the extra shield is pushing it over the edge so to speak.

Thanks again for the thoughts, will do some tests with jumping those conflicting pin.

Mike.

AussieMike
Posts: 3
Joined: Wed Apr 08, 2020 12:00 am

Re: LCD issues with 3 or more shields stacked.

Post by AussieMike » Wed Apr 08, 2020 6:14 am

Hi Brissieboy,

I've tested with the 4 conflicting pins (3,5,6,9) isolated and jumpered directly from the Eleven to the LCD without success.

Same results as previously. The N drive inputs don't seem to have caused the problem on the LCD.
Probably still a good idea to isolate the conflicting pins though.

Any other ideas?

Mike.

Brissieboy
Posts: 206
Joined: Fri Sep 20, 2013 7:25 am

Re: LCD issues with 3 or more shields stacked.

Post by Brissieboy » Wed Apr 08, 2020 7:07 am

If your LCD shows just shows those dark blocks it looks like the LCD is not getting any data. I would be looking around D8 (E) and D9 (RS) for starters.
Have you done a good physical inspection of the N-Drive to ensure there are no physical problems such as solder bridges or other problems?
You could try incrementally connecting the N-Drive with just Vcc & Gnd first then adding each individual pin to see when it fails.
I am assuming that you are using the same sketch for each test.

Brissieboy
Posts: 206
Joined: Fri Sep 20, 2013 7:25 am

Re: LCD issues with 3 or more shields stacked.

Post by Brissieboy » Wed Apr 08, 2020 11:05 pm

Also check that the LCD shield does not have any connection from the contrast pin to the header which might be corrupting the contrast setting. It should just have a small potentiometer onboard (no external connection) to adjust this but there are quite a few variations of the LCD shield out there.

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