First sample tested

A project log for [WIP] Solar powered supercap balcony lights

Purpose of this project is to create batreryless light for balcony.

andrey.malyshenkoandrey.malyshenko 11/21/2019 at 20:220 Comments

Okay, i assembled first version. Fabricating and soldering went well despite some doubts that i had due to elements and track sizes

Few issues were found quite to my expectations. Mostly due to mistakes in my design.

1. Enable pin didn't work on mcp1640, it stays on forever, for now not sure why. Possibly i did get ic version without this feature (if that's even possible). 

2. More importantly regulation didn't work as expected. I didn't put current regulating resistor in series with output LED, therefore i effectively tied regulator output to forward bias voltage of LEDs making its work impossible. Due to this current went well above my calculation and current shunt sensor sent ~2v to feedback pin of voltage regulator. This is well above required 1.2v and therefore regulator saturated driving whole chain to balance point way above my expectation.

Here is updated schematics

First of all, i want regulator to drive it's output to ~5 volts as it is designed to. Therefore to keep power wasted on resistor down i put LEDs in series, with this configuration i expect voltage on the ouput to be ~5.5v, with total voltage drop of 5v this shoul leave 10 Ohm resistor .5v, therefore driving whole chain towards 50mA current. This will give me 50mv voltage across shunt resistor, and with gain factor 50 i'll expect 2.5 volts on feedback pin of INA199. Therefore i send it back to regulator through resistor voltage devider that i'll set on 1/2 for now and adjust later.

Here is updated pcb layout and i'm currently working of fabrication of second prototype