Arduino Uno/Nano phone (SIM800) project questions

[f82]

Hello everyone,
I'm new to the Arduino world and come from the Raspberry Pi one always used more as a computer replacement than a real low level microcontroller.
Lately I'm becoming interested in this world and I have a background know-how from pc modding and eletronic in general but completely new to this one. I'm reading many articles and tutorial and I'll receive soon many components.

My first project idea, being a fan of old-style phone, was to built a fully functional GSM phone with keypad and a simple LCD or OLED for both sms and calls. Actually I got two UNO boards both v3, a generic kit with the classic dual line blue backlighted LCD many components, also another official starter beginner kit. I'll get soon:
-a generic NANO v3 board
-a 16 buttons keypad,
-the OLED 128x64 display (but with no library as much as I read after bought it),
-a SIM800L module with SPK and MIC points (don't know if 5V fixed or the old one I'll see),
-a DC-DC step down LM2596 2A regulator,
-a DC-DC step up 2A MT2608 (up to 5V-28V) regulator,
-already have many 3,7v LiOn phone batteries I could use, 
-a 4 AA Ni-Mh battery holder case if I'd go for a 6v/4,8v alternative
-a TP4056 LiOn protection chargers
-10K ohm resistors (someone said it's needed for the TX line from the arduino to the SIM800 module to reduce Vin HIGH)
etc...

Now, beside how much it will be difficult to write the code I'd like to begin understanding some things and once I'll receive the components I'll update here with more questions.
To begin:

1) if I use the DC-DC step UP regulator can I use ONE single li-on 3,7v 1500mah (ex.) battery to give power to both the arduino (uno or nano) AND the SIM800L board? I understand the gsm module will ask up to 2A of power so I imagine I can't use the 5v or 3.3v lines from the arduino itself. Or maybe it is better to power the arduino with a 9V classic battery and a 3,7v big battery for the gsm module separately? Cause if I use the NANO I can't use the 9V without the step-down converter, if I use the UNO everything will become big and not good looking for modern phone and I still have to find a good looking plastic case.

2) to use the classic LCD (with the dual asic on the back the one with the starter official kit) do I need some serial converter or external module to write to it? And the generics oled display does need some serial converter too?

3) beside the youtube tutorials, someone here has built a good stable and functional similar project with a clear guide to follow? I've seen many choosed different roads for both wirings and codes.

Thanks for the initial answers.
Bye

[ronaldgadget]

This is not so difficult. I have several GSM shields that I use in remote places to turn on / off things using SMS commands.

The thing that cost me oodles of time is the undocumented assumptions in the GSM library - the use of AT commands is quite tricky. As my system is remote, and must work at all times, I have the 'watchdog' function enabled in the arduino, and the GSM library cost me many headaches getting to get both working reliably. For instance, the 'send SMS' library call does not return if the GSM connection is lost (I did mention 'remote area' with varying reception quality). To me it is inexplicable why sendSMS does not return when GSM connection is lost(It should return immediately with an error) - this took months of debugging (elapsed time, not hours of work) to figure out. The undocumented 'features' of the library and the AT commands (which vary from module to module!!!) is a problem.

I do not know where you live, but here in CH, GSM modems will be phased out in 1 year. So, your efforts to get this working may not be worth the investment in the SIM800L - I strongly recommend you get an LTE modem.

I now need to get all my GSM/GPRS shields replaced with LTE and adjust the calls...

Ronald

[f82]

This is not so difficult. I have several GSM shields that I use in remote places to turn on / off things using SMS commands.

The thing that cost me oodles of time is the undocumented assumptions in the GSM library - the use of AT commands is quite tricky. As my system is remote, and must work at all times, I have the 'watchdog' function enabled in the arduino, and the GSM library cost me many headaches getting to get both working reliably. For instance, the 'send SMS' library call does not return if the GSM connection is lost (I did mention 'remote area' with varying reception quality). To me it is inexplicable why sendSMS does not return when GSM connection is lost(It should return immediately with an error) - this took months of debugging (elapsed time, not hours of work) to figure out. The undocumented 'features' of the library and the AT commands (which vary from module to module!!!) is a problem.

I do not know where you live, but here in CH, GSM modems will be phased out in 1 year. So, your efforts to get this working may not be worth the investment in the SIM800L - I strongly recommend you get an LTE modem.

I now need to get all my GSM/GPRS shields replaced with LTE and adjust the calls...

Ronald

The idea was building a good looking vintage style stable gsm phone for only making an receiving both calls and sms like a 90's phone. I know the code will not be easy, every tutorial seems to use different ones for similar projects and I was thinking to use the simplest possible libraries and not many code lines.
I think that 2G maybe depending of which country will live a bit longer than many says, cause I imagine many companies are still using it for their industrial/automation communications.
I would expect 3G to be the first to be retired but who knows, it's just a hobby project to have an assembled phone to use everyday. I still like the few modern keyboard feature phones and ironically most of them are using the same processor of these modules.