I have bought 3 different kinds of lcd's and been working 3 weeks and cannot figure out why the LCD's don't work. I will past what I bought below, but let me get some things out there.
WHY do the examples use the analog pins?
that seems like a total waste.
I want to use spi because I need a bunch of pins to do the project I need to do.
So here's the issue.
I have bought 3 different styles of 3.5 inch displays, I have got all them working with the examples and I can print stuff on the screen any way I want. BUT.... As soon as I take the display off the the mega and use jumpers to connect to it the displays only give me a white screen. I've tried direct jumpers, Jumpers to a project board. I've tried 3 different megas and several displays and every one is exactly the same.
My goal is to use as few pins as possible for the lcd. I haven't shown code because all I've done is to use the examples.
the more I read the more it seems like I can use about any 4 pins to do spi to the lcd. but no matter what I do I can't get the lcd to work on jumpers.
I don't know if i have changed the examples correctly to use other pins because I never get it to work unplugged from the mega.
In all examples I've seen I've never seen anything about pull up or pull down resistors. I've taken a scope and monitored the pins and I see data on the pins, I don't have a scope with spi debug so all I really see is the data stream and it looks similar to the pins when they are plugged into mega connectors.
Then it's pretty clear there is nothing wrong with the Megas, nothing wrong with the displays, and nothing wrong with your code...........
But probably quite a lot wrong with your jumpers - all of which are a total mystery, and only one needs to be faulty for a total stuff-up.
Well, it shouldn't be, it should be to use exactly the number of pins the displays you have bought require.
I appreciate that you can't know how well I wired it. but I've been breadboarding circuits since 1987, I have wire wrapped complete motherboards with all associated hardware. I have wired it with male to female pins from 2 different kits. I have wired it with Male to male pins to a bread board, I have wired it with straight wires, I bought this
I took a scope and verified the signal going to the lcd.
Has anyone had to put pull up or pull down's on these lines.
I spent 22 years troubleshooting electronics on 40 hours a week, I have trained 2 generations of technicians for my company. I am a pretty decent troubleshooter. but admittedly new to the Arduino world.
At best, that screw terminal thingy might move the problem, without actually solving anything. That hiletgo display comes on its own shield to plug straight onto a Mega. It is clearly stated as 16 bit parallel device, and the pinpattern clearly described. If you want the display remote from Arduino, all you need is a couple of ribbon cables and match pin for pin as required. The SPI only alludes to the SD slot, which you may or may not need.
It might help if you read post #6 again - three times might suffice. I assume you have that device, it is not an SPI device and no amount of alteration to the library will change that fact. Even if it was a dual interface device, the last thing you do is edit the library.
It appears that the same applies to the fainwan display, which seems to pass up the 36 pin set and uses analogue pins as digital.
If you really want an SPI device, your best option is to go out and buy one. Having said that, it might not be such a great idea, and it depends on your real needs rather than merely perceived ones.