After reading extensively about the Nokia 5110 display online I think that I cumulated more confusion than when I started ...
From what I understood there are couple different types of breakout boards for the Nokia 5110 out there. Some provide an on-board logic shifter (5V -> 3.3V) to allow for direct connection to the Arduino digital Pins, and some that don't. In my case, I think that the SparkFun breakout does not come with an internal logic level shifter ?
If this statement is correct, I understood that there are several ways to provide the needed 3.3V to the Nokia 5110 from the Arduino.
1°) Using a logic level shifter such as this and hook up all the digital PINs from the Arduino controlling the screen to the shifter.
2°) Ignore the 3.3V limit and control the screen with 5V...
3°) Hook-up the Digital PINs controlling the screen to voltage dividers to shift the voltage to 3.3V.
Since I had a couple of resistors laying around I decided to try out the third option. I went with a divider made of 2.2kΩ and 1kΩ resistors : Vout = (VinR2) / (R1 + R2) = (52200)/(1000+2200) = 3.43V.
Is the value of 3.43V acceptable for the display ?
Should I go for a couple of higher value resistors to avoid to much leakage ?
Should I add a resistor to limit the current to the display on top of the voltage regulator ?
Can I connect a Digital Pin of the Arduino to a voltage divider and to the Backlight Pin of the screen to turn On and Off the Backlight at will ?
If I decide to transfer the project to a Standalone Arduino, how can I provide 3.3V to the Vcc pin of the Nokia 5110 ? Can I also provide the 3.3V via a voltage divider ? Or is it better to use a Linear regulator in this case ?
Tomtop:
From what I understood there are couple different types of breakout boards for the Nokia 5110 out there. Some provide an on-board logic shifter (5V -> 3.3V) to allow for direct connection to the Arduino digital Pins, and some that don't.
The only difference in breakout board that I am aware of is that some have the backlight pin connected to ground. The display can be powered off Arduino's 3.3v pin. The various signal wires are 5v tolerant. I'm sure powering it through a voltage divider would be fine. You should always provide a resistor in the backlight circuit. The backlight is largely ceremonial and you only need it if you are operating it in the dark. Backlights can come in different colours. I think you should choose white. Blue is promoted as "cool". It isn't.
In the long term I was planing to transition into a standalone configuration for the project and Im powering the whole thing via a 12V, 2A power supply that I feed into a buck-converter to get the stable 5V that powers the ATMEGA328. Do you think that I can use a linear regulator such as : this from the output of the buck-converter to Vcc of the Nokia 5110 display ?
If the pins are 5V tolerant I guess that I just add limiting resistors in series to limit the current ?
Would you have any idea of the current drawn by the backlight from such displays ? Im just curious if a Digital pin from an Arduino could handle directly switching them on and off ? Maybe a 330Ω resistor would do the trick ?
Tomtop:
Do you think that I can use a linear regulator such as : this from the output of the buck-converter to Vcc of the Nokia 5110 display ?
If the pins are 5V tolerant I guess that I just add limiting resistors in series to limit the current ?
Would you have any idea of the current drawn by the backlight from such displays ? Im just curious if a Digital pin from an Arduino could handle directly switching them on and off ? Maybe a 330Ω resistor would do the trick ?
A little 100mA regulator like that would be fine but, if you are buying rather than dipping into the parts bin, I think you should get one that is good for 3.3v.
I have never used limiting resistors on the signal lines, but some people have.
I'm afraid I don't know about the backlight current. I imagine you could switch it. I have a jumper on the shield but I never use it. I use a 560 ohm resistor.