Diodes Work Better One Way

A project log for SOL: Long-term solar intensity sensing

SOL is a project to develop a solar powered, connected solar intensity sensor (also known as a pyranometer)

Jake WachlinJake Wachlin 10/03/2018 at 01:000 Comments

As I said in the previous project log, the voltage measured in the IV sweep seemed low, compared to what I expected for the solar panel and based on what I saw on SOL V1. Suspiciously, the voltage seemed to be clamped at around 0.75V. This solar panel can theoretically reach an open circuit voltage higher than the max input voltage of the battery charger IC, so I added a zener diode as a voltage clamp. The 0.75V seemed suspiciously similar to the forward voltage of the diode. Indeed, when I double checked the board, the diode was soldered backwards. I removed the diode, and re-ran the IV sweep test. Now, under a desk lamp, the max voltage is up to about 5V, which is much more realistic. Ill have to wait for tomorrow to see the measurements under sunlight, but I'm expecting good results.

Through assembly and testing, I've also found a number of other issues with this build. I had accidentally run the trace for the temperature sensor output over a ground trace, so it is unable to measure temperature (I may attempt to cut the trace to get it working.) I also forgot a decoupling capacitor for the ADC, although the ADC seems to still be working OK. I will likely make a V2.1 design that makes some of those quick fixes soon, but am waiting to get V2.0 fully tested first.