Arduino Due - which shields can I use / what's the 5V pin good for

Hi,

I was running into memory issues (large Array) on my UNO, so I thought about buying a Due. My question(s):

can I use the 5V pin to supply power to an LCD like this one:

https://www.aliexpress.com/item/4000510200782.html

I read

Unlike other Arduino boards, the Arduino Due board runs at 3.3V. The maximum
voltage that the I/O pins can tolerate is 3.3V. Providing higher voltages, like 5V to an I/O pin could damage the board

does that mean that a shield like the LCD above is prohibited for use with the Due, i.e. a shield must not draw more than 3.3V FROM the Due? Or does that only mean that a shield must not supply more than 3.3V TO the Due? Or BOTH? If the latter what is the 5V pin on the Due good for (when it serves as a VCC)? btw, does that LCD only draw 5V or is there a 5V voltage on the input pins as well?

and another question: I would like to connect this button keypad

https://www.aliexpress.com/item/32969265728.html

but it doesn't seem to have VCC or GND pins, does that mean it runs without them / is the power supplied via the I/O pins? In general: do the I/O pins supply voltage on their own?

I know those are probably beginner questions but I couldn't find specific answers to them.

Cheers
step1

You can use the 5V pin to supply power to external electronics.
You can use the 3.3V pin to supply power to external electronics.

Both pins can supply substantial current. Look in the spec.
In contrast to the Uno whose 3.3V pin is intended for less than 50mA.

Most electronics is designed for 3.3V i.e. it will understand the Due's output signals
You only need to worry if a shield level-shifts up to 5V because the designer only intended the Uno target.

You must not have any input signals > 3.3V

This applies to the I2C backpack in your first link.
Remove the backpack pullups (that are pulling up to 5V). The Due has onboard I2C pullups to 3.3V

If you are worried about a commercial shield, post a link to it. (preferably a clickable link)
Then a member might be able to advise suitability.

David.

thank you David for explaining things to me. As I am new to electronics I have to look up a lot of acronyms and try to understand them. Back to your reply, I have some questions for clarification:

david_prentice:
You can use the 5V pin to supply power to external electronics.
You can use the 3.3V pin to supply power to external electronics.

does that mean I can only power things like LEDs, speakers etc that are only connected to the 5V/3.3V pin and GND but which are otherwise unconnected to the board?

You must not have any input signals > 3.3V

This applies to the I2C backpack in your first link.
Remove the backpack pullups (that are pulling up to 5V).

by input signals you mean input to the Due, right? And by I2C backpack you mean the LCD I guess? (there are different parts offered in that link). How do I "remove the backpack pullups", do I do that by code or by (re)moving jumpers on the board and how/ which ones? Is that fourth part in the offer a LLC and can I use that to convert the LCD's voltage from 5V to 3.3V so that I can use it with the Due?

here's the (clickable) link again:
https://www.aliexpress.com/item/4000510200782.html

Cheers
step1

The 5V and 3.3V pins on a Due can power external electronics up to a few 100mA

ARM GPIO pins are wimpy. You must not connect any heavy loads e,g, motors, relays, backlights, ...
ARM GPIO pins can manage a single LED.
Most ARM port pins provide logic output or input i.e. low-current signals.

The LCD in your link only needs 3.3V to work. But the contrast pin (#3 on the LCD) needs to be 4.5V less than VCC. The only reason for 5V is that it avoids a negative voltage supply. 5V - 4.5V = +0.5V whereas 3.3V - 4.5V = -1.2V

There are I2C pullups on most backpacks. Look for SMD resistors marked 472. Remove them with a soldering iron.

The 4th item is a breadboard power supply. You do not need it.
Your Due has already got power from its USB cable.
The LCD + backpack (item 1 or 2) will work fine from the Due.

I prefer the Green LCD. Works with or without backlight.
The Blue LCD only works with backlight. And white on blue looks pretty horrible.

David.

david_prentice:
ARM GPIO pins are wimpy. You must not connect any heavy loads e,g, motors, relays, backlights, ...
ARM GPIO pins can manage a single LED.
Most ARM port pins provide logic output or input i.e. low-current signals.

I hope I'll be able to use a Nema17 motor on it like here:

I've been using the UNO for it so far.

The LCD in your link only needs 3.3V to work. But the contrast pin (#3 on the LCD) needs to be 4.5V less than VCC. The only reason for 5V is that it avoids a negative voltage supply. 5V - 4.5V = +0.5V whereas 3.3V - 4.5V = -1.2V

There are I2C pullups on most backpacks. Look for SMD resistors marked 472. Remove them with a soldering iron.

yes, there is the Arduino IIC/I2C interface on my Display (it says it "was developed to reduce the IO port usage on Arduino board"), I suppose I won't need to solder the other pins above the LCD then. Yes, there are three 472 SMDs on that interface (/backpack, now I know what you mean :slight_smile: ). So if I remove them (I am very bad at soldering but as long as it's only removing not attaching I may stand a chance :)) and then connect GND to GND and VCC to the 3.3V pin plus the SDA and SCL pins I can use it with the Due, right?

I prefer the Green LCD. Works with or without backlight.
The Blue LCD only works with backlight. And white on blue looks pretty horrible.

I have the blue one because I thought that would be suitable for use in the dark.

Cheers
step1

Your stepper motor controller will be fine. The external controller board takes low current logic signals but its output drives a high current motor.

You remove the backpack pullups.
You connect the backpack VCC to 5V pin on the Due.

David.

okay! thanks again for your help David :slight_smile:

Hi,

I am working with stepper motors and stepper driver CL57T to be controlled by arduino mega. However its clock speed is not enough so I decided to use the Due because of its higher clock speed.

Can I use it? Keep in mind that the CL57T works with 5v input signal while the Due can only supply 3.3v.

Thanks

Abdalla