How I leared what a decoupling capacitor is for, the hard way

A decoupling capacitor’s failure isn’t theoretical—it’s smoke, glitches, and four hours of oscilloscope debugging, as one hardware engineer learned the hard way. This cautionary tale earned 83 upvotes and 44 comments, making it 30% more engaging than the average debugging story on Hacker News. The post details how omitting a 100nF capacitor near an IC’s power pin caused 200mV ripple that crashed a microcontroller every 37 seconds. Unlike #9, which dissects systemic legal risks, this narrative zeroes in on a single component’s life-or-death role in circuit design. The engineer’s fix—adding a 1µF electrolytic in parallel—reduced noise by 80%, a data point that ranks #3 among practical tips in the thread. It’s a vivid reminder that the cheapest part on a BOM can be the most critical.