Making my cheap flashlight USB-C compliant

A few years ago, I bought a tiny flashlight on AliExpress for about $10. I carry this super handy flashlight everywhere I go; it’s smaller than a AA battery and it is significantly brighter and more useful than my phone’s flashlight. Unfortunately, like many super-cheap USB-C devices, the USB-C port is not compliant with the USB-C standard. Consequently, the USB-C cables I use to charge my phone, laptop, and battery bank will not charge this flashlight. While I can use a dedicated USB-A to USB-C cable to charge the flashlight, carrying such a cable around is inconvenient and (in my opinion) defeats the purpose of USB-C.

After a few frustrating years of inconvenient charging, I finally had enough and decided to take matters into my own hands. I began by disassembling the flashlight and carefully examining its circuit board.

The issue was just as I expected: either due to sloppiness or as a cost-saving measure, the engineers excluded two tiny resistors from their circuit design.

USB-C-compliant electronics use two 5.1kΩ pulldown resistors to detect when they are plugged in. Without these resistors, the USB-C charger cannot tell when a USB-C device is connected, so it doesn’t provide any power. (The reason USB-A to USB-C cables allow the flashlight to charge, is because USB-A doesn’t check for the presence of the resistors.)

Counting the pins on the USB-C socket revealed that while the socket lacked the pins needed for USB data transmission, it had unused pins for resistors on the “CC1” and “CC2” lines. Some quick googling for “power only USB-C socket” got me the pinout I needed. My goal now was to bodge SMD resistors into the circuit, each with a value of 5.1k ohm. Thankfully, I had these parts I needed in my SMD assortment kit. These resistors needed to connect from the middlemost pins of the USB-C socket to ground.

Working under a microscope, I decided the easiest way to achieve this bodge was by soldering the tiny SMD resistors between the CC1 and CC2 pads and the grounded exterior of the USB-C socket itself. After putting a small amount of solder on both the SMD resistors and the exterior of the USB-C socket, I used a combination of tweezers and hot air to secure the resistors in place. This was painstaking work, but I managed it after a few minutes.

I put the flashlight back together and tested it out with a power bank. Success!!! Now I can use whatever USB-C cable I want, rather than needing to pack a spare USB-A to USB-C cable on trips.