Thursday, October 8, 2020

Reverse engineering my cable modem and turning it into an SDR

This is the type of nerdy hacking that makes me jealous.

After removing a few screws from the plastic housing to get access to the board, my first thought was to look for UART headers to take a peek at the serial console. After identifying two candidates consisting of four vias surrounded by a rectangle near the edge of the PCB, it was time to identify the pins. Using a multimeter, the ground pin can be easily identified by checking the continuity with one of the metal shields on board. The VCC pin can be identified by measuring the voltage of each pin when powering on the board. It should be a steady 3.3v, or in some cases 1.8v or 5v. This pin is not needed, but is still useful to identify the operating voltage and eliminate one candidate for the Tx and Rx pins. While booting, the Tx pin will sit on average a little lower than the VCC pin and drop much lower when a lot of data is being output. This leaves the last pin as Rx.

No comments:

Post a Comment