Enclosure and batteries

A project log for OSH VFD Watch

Open source vacuum fluorescent display watch.

MileMile 03/30/2018 at 21:500 Comments

This week batteries arrived. They are lithium polymer 4 x 10 x 30 mm with declared capacity of 110 mAh. First thing to do was to measure battery capacity in my application.

Procedure was to charge the battery up to 4.2 V and then discharge it with 45 mA (maximum current draw of the watch is 35 mA + some reserve) to 3 V.  In Version 1.0 battery is not usable below 3.3 V, therefore I will drop 3.3 V rail to 3 V in the next version. Measured capacity was 86 mAh or 2 hours of active run time. With 30 min active time per day that would be autonomy of 4 days. I might add another battery, that would reduce current draw from single battery and get me maybe 100 mAh per battery. I think that should give autonomy of about 10 days.

I also tried printing enclosure with PLA and 0.1 layer height. Enclosure turned out good but further tweaking and optimization is required. For now time required to print is 3 hours and supports are only needed for small indent for pcb and back cover what was not the case for first (not version shown in image).