Using the Nokia 5110 LCD with the fewest system resources

I had a project that needed some live data display, and looking for the cheapest low-power solution for our loggers lead me to the Nokia 5110 LCD. Once you get the backlight current under control, you can power the entire display from a digital pin, and if you use shiftout for soft SPI you can then get rid of the Reset and CSelect control lines. This brings the display down to any four wires you can spare on your build (incl. the power pin) and a ground line. This is much more manageable than what you see with the standard hookup guides if your mcu is I/O limited like our pro-mini based loggers:

Adding the Nokia 5110 LCD to your Arduino Data Logger https://thecavepearlproject.org/2018/05/18/adding-the-nokia-5110-lcd-to-your-arduino-data-logger/

EKMallon: Once you get the backlight current under control

I submit a likely best way to get the backlight "under control" is to disconnect it. It is usually redundant, and can even be a hinderence.

I also add an inline slide switch to do just that most of the time. But many of our loggers get deployed in caves, so its nice to have the option of the back light when its needed.

These Nokia 5110 displays are mostly reclaimed ones for mobile phones.

They are fine for some projects and one of the few displays that are readable in direct sunlight.

They are in my experience of very questionable reliability and if your application does not require the display to be read in direct sunlight I would use something like on of the SSD1306 OLEDs, they are 4 wire too.

srnet:
I would use something like one of the SSD1306 OLEDs

Indeed. And you can get a quite useful eight lines of text on them. Further. I used

#include "SSD1306Ascii.h"
#include "SSD1306AsciiAvrI2c.h"

which I understand are very space efficient - as well as wire-efficient

Those OLEDs are great looking displays. I will probably use them on any instruments that only see operation for short periods (like during a dive). I'm wondering if they might handle the pressure of being under water better as well?

For long-ish deployments (a year or more) I'd have to setup a switching system to enable/disable them - otherwise that ~20mA would be too much power to have them turn on for every sampling event.

And when the e-paper displays get cheap, I'll try them out too...

EKMallon: I'm wondering if they might handle the pressure of being under water better as well?

I can't imagine they would be any less competent than the 5110, simply by virtue of being more modern. I imagine they only need be turned on for as long as they are being read, so I don't see a power problem.

I'm a fan of 5110s, but I'm seriously impressed by the OLED and I doubt I would buy another 5110.

I started with the Nokia 5110 LCDs and found better ones recently. The HX1230 is a good replacement. It's higher resolution (96x68 versus 84x48) and uses less power (470uA versus 173uA). The cost and size are similar. Another good replacement are the 7920/UC1701 128x64 LCDs. They're also lower power (275uA).