lcd rgb - arduino micro powerfull enough ?

Projects General Guidance
1

Hello,

I bought this lcd with rgb backlight (comon anode)

https://www.aliexpress.com/item/color-1602-16x2-lcd-display-module-RGB-LED-backlight-LCM-ADM1602K-FS-RGB-FBW-high-quality/32894884921.html?spm=a2g0s.9042311.0.0.10654c4dnOXA07

from the specs

red 10mA
green 15mA
blue 15mA

can the arduino mini pro power the rgb back led or do I have to use transistors ?

regards

2

Yes. The ATmega32U4 chip has the same specs as the regular ATmega chips which is 40mA per output pin "absolute maximum" and a total overall maximum current of 200mA.

And, if those are the maximum ratings for the LCD backlight you don't have to drive the LEDs at full power.

3

Do use current limiting resistors.
Use Ohm's law: R = V / I

For example, if you have a supply of 5 V and an LED with a forward voltage of 3.2 V, it means that you have to have a voltage drop of 1.8 V over the resistor. If the forward current for the LED should be 10 mA, that means that you need a resistor of 1.8 V / 0.010 A = 180 Ω.

The forward voltages in the specs of the display for the red and green LED seem rather high, so I'd take them with a grain of salt.

Pieter

4

the issue here is that the arduino is 3v power and also I would have to invert values in the code

5

The LCD specifications only mention a supply voltage of 5V, does it even work at 3V? Not all do, in my experience.

For the LEDs, indeed VF as listed is really high. 3.3V is a bit on the high side for blue but possible; normal for red is about 1.8V, for green about 2.0V.

Not sure how to power blue on 3V - maybe use a 10Ω or so resistor? At 3V it will conduct, just not fully!

DVDdoug:
Yes. The ATmega32U4 chip has the same specs as the regular ATmega chips which is 40mA per output pin "absolute maximum" and a total overall maximum current of 200mA.

OP mentions Pro Mini which should be the ATmega168 or 328. The ATmega32U4 is for the Pro Micro (I'm also always confused between the two... horrible naming). Current ratings are the same indeed.

6

yeah the naming sucks

the lcd itself works on 3V, I guess I'll use transistors with an external 5v power supply to be on the safe side and not needing to invert HIGH/LOW in arduino code

7

Why invert? If you use an NPN to drive your LED it's still HIGH signal for led ON.

8

wvmarle:
Why invert? If you use an NPN to drive your LED it's still HIGH signal for led ON.

well they are kathode driven, but I use a transistor so it is ok
figured the mini pro vcdc pin was 5v in the end, but sda/scl are 3v so it works in the end