# HG changeset patch # User Mychaela Falconia # Date 1623386066 0 # Node ID 38bcb9425df014a832970927596c1b05834f20d1 # Parent cb8d43a5023c12f9ae396f49dc963436aec62e99 FC-handset-state: battery documented diff -r cb8d43a5023c -r 38bcb9425df0 FC-handset-spec --- a/FC-handset-spec Fri Jun 11 01:47:22 2021 +0000 +++ b/FC-handset-spec Fri Jun 11 04:34:26 2021 +0000 @@ -680,3 +680,30 @@ Because our firmware will be designed for a simple on/off vibrator control, during fw development on the Venus board it will be trivial to use a LED to simulate the vibrator on/off state. + +1.10. Battery + +The battery in our FC Libre Dumbphone handset will be single-cell Li-ion. It +goes without saying that this battery will be freely removable and replaceable +by end users. The specific size, form factor and mAh capacity of this battery +won't be addressed until later in the project, when we get closer to building +the actual handset. + +Our Calypso+Iota chipset dates from the era when the cellular handset industry +was transitioning from NiMH to Li-ion batteries, and the Battery Charger +Interface (BCI) block in the Iota chip supports both battery types, or at least +TI's documentation claims so. Given that we are going against the mainstream +society's ideas in so many other ways, I have given thought to the possibility +of using a NiMH battery instead of Li-ion. However, the problem with using a +NiMH battery is that we would be going into completely uncharted territory +without any guidance. In the case of Li-ion batteries the charging process is +well-understood in both theory and practice, and our FCHG logic based on reverse +engineering of Pirelli's firmware works well both on the same Pirelli and on +Motorola C1xx family. In contrast, if we went with NiMH, we would have +absolutely no guidance in implementing the necessary charging control logic +(TI's LCC code is useless), causing a huge risk to the project. Furthermore, +determining the state of charge from Vbat for the purpose of the bars icon is +already somewhat challenging even with Li-ion, given the relatively flat middle +part of the discharge curve - and with NiMH we can only expect the problem to be +even worse, as their discharge curve is said to be even flatter. For these +reasons, we are going to play it safe and stick with Li-ion.