I’ve finally received my new test phone from Amazon, since the one I ordered from China is still somewhere between China and France because of the Covid logistics slowdown.
This is also a Redmi Note 7 (4GB Ram + 64GB Flash for this one), cost is 130€ from Amazon FR.
Unfortunately the bootloader is locked, meaning we’ll have to wait at least 7 days to unlock it, but we can still prepare it for development purposes.
As the phone will be powered 24/7, we MUST remove the Lithium-ion battery and power it with an external source of energy
After removing the back cover (there are plenty of tutorials on Youtube), I removed the battery and soldered a socket to provide power, fake the electronics about battery (ID and temperature), and also gain access to the debug serial port.
The socket is fixed in a 3D printed part, taking place in the battery location. The phone itself is placed into a frame which I expect to fit in a kind of ‘slot card’ to build servers. More on that in few days.
The phone has no problem running like this but we should take care of the power supply. During the boot process, the current peak apparently goes above 4 Amps. No problem when running from batteries, but the external power supply must be correctly sized.
Running at 4.0 Volts, the phone believes it is charged at 67%, and the fake battery temperature resistor is read as 21°C.
