Discussion
I get an impression there's a decent market who regrets the shift to smartphones, so how would I assemble a dumbphone? Out of existing components?
For starters: I'd fork https://mikrophone.net/ !
Though I'd replace the touchscreen subsystem & i.MX 8M Plus "app" ARM core. I presume these were included for the sake of apps you're (yuck!) obligated to use.
Maybe I'd have model that removes or replaces the untrusted ESP32 with its WiFi & BlueTooth, but there's still a strong need for it.
1/4?
From mikroPhone I'd leave:
* SiFive Freedom E310-G002 (RISCV) microcontroller
* SIMCom SIM7600X or Quectel EC-25 modem (interfaced to the microcontroller via the untrusted ESP32, or replacement SiFive Freedom)
* An audio subsystem consisting of:
- 2xMAX98357A Class D amplifier
- PCM1770 headphone amplifier
- ICS-43434 MEMS Microphone
- MAX9814 microphone amplifier
* Ardu-Cam
* SD card reader
* Other sensors
Despite my hopes... I'd need to tweak the firmware to expose an API for our UI.
2/4?
I want a more retro UX than the mikroPhone's, something you could hopefully forget about charging for months if not years on end!
And something that reaches my standards for text-handling.
So I'd include a 2nd (or 3rd) SiFive Freedom with the smallest QSPI chip I can find. That appears to be 16MiB... Plenty to hold a full-Unicode font & the code to render it!
I'd use a small black/white/red/yellow eink display, say the EP37YR. Include an LED & toggle-button to illuminate it at night.
3/4!
To have expressive enough user input to serve as a keyboard (even if you would need to learn it) I'd include a joystick like the KY-023. Or an equivalent we could solder onto the main circuitboard. Perhaps replace or remove the knob for a lower profile.
Since the SiFive Freedom needs binary input I'd hook the analog joystick up via a quad-comparator (like the LM399) to 4 digital input pins, 5 counting its button.
Include 2 more buttons on either side, one hooked up to the wake-pin.
4/4 Fin!
Oh, I'll add that those input controls (with 4 compators & 3 buttons, counting the button in the joystick) would use 7 input pins. Maybe an output pin to power the joystick when needed, saving miniscule power.
Also I could consider hooking the camera & SD card reader directly up to this UI processor, or the MCU could add useful abstractions.
In future threads I'll assume that mikroPhone's firmware works, & focus on my choice of UI.
5/4!
@alcinnz The arm underneath all the i.mx is a great lil chip very linux friendly, which makes it android friendly too, the bolted on tech in that module is most of the needed memory, video, audio, cell, & radio hardware.
https://www.toradex.com/computer-on-modules/verdin-arm-family/nxp-imx-8m-plus
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