Hardware Mod: RTC on the Miyoo Mini Plus Miyoo Mini
Proper RTC mod has now also been achieved on the Miyoo Mini by adding a 3.3V LDO regulator to VBAT The SoC was removed and the trace cut in the same way as on the MMP
Proper RTC mod has been achieved by removing the SoC, then cutting a trace beneath the SoC that connects AVDD_RTC to VDD and then doing the mod.
No more LED lighting up or powering parts of the system. Current draw down to 33uA
The need to remove the SoC makes the mod even less accessible for an average user.
RTC (real time clock) can be very useful in games such as Pokémon.
The Miyoo Mini plus's SOC, Sigmastar SSD202D, has a low power RTC built in, but it is not connected on the pcb (Pin 17). which is connected to VDD underneath the SoC, so it only works when the device is on.
From the Datasheet:
Feature list:
Pinout:
Specs:
On the PCB:
The PMIC on the MM+ (AXP223) has an always-on voltage output for RTC applications that can supply up to 30mA (Pin 46):
Specs:
Pin list:
Pinout:
Kyek has found these points where this 3V rail might be taken from:
He also traced what else is connected to this rail:
Connecting VCC_RTC(AXP223) and AVDD_RCC(SSD202D) does in fact work, as the clock keeps going even if the device is turned off.
This is how I connected them:
To make sure that OnionOS does not restore the time from currentTime.txt, I commented out line 538 of /.tmp_update/runtime.sh
# date +%s -s @$currentTime
The pins on the SSD202D are tiny (.35mm pitch), experience in microsoldering and use of a microscope is advised.
It does have side effects, which need to be researched:
- The green power LED is always on after the mod (I removed the LED from the board)
- There is a constant power draw of 11.4mA (10.4mA without the LED)
The RTC should only draw single-digit microamps, so it seems that the mod somehow forces other components on.
As it stands, the mod is not easily done by an end user (especially soldering to pin 17 on SSD202D),
it might be possible to design a flex cable to easily interface with pin 17 and make this accessible for everyone with a soldering iron.
Thanks to everyone who was there holding my virtual hand while testing - tGecko