See how Ben Eater reverse engineered an ’80s TV-censoring gadget

Again within the Eighties, there existed a chunk of {hardware} referred to as the “TVGuardian,” which might try and censor incoming video in real-time. As just lately coated by the great YouTube channel Expertise Connections, the TVGuardian reads captioning knowledge because it’s despatched after which replaces the unhealthy phrase(s) with another phrase and likewise mutes the audio.

Upon studying that the interior dictionary of offensive phrases isn’t listed wherever within the guide, Ben Eater had the thought to extract it himself. After a fast teardown, he found a single 93LC86 EEPROM chip functioning in 8-bit mode for a complete of two,048 8-bit phrases. He then related an Arduino Uno to the EEPROM’s SPI bus and skim 16-byte chunks earlier than dumping the contents to the serial monitor for additional investigation.

One of the vital attention-grabbing findings that Eater found was how the phrases have been encoded in blocks of 256 bytes separated by a protracted string of null characters. Each unhealthy phrase is an array of bytes for the ASCII characters themselves together with a terminating character and an additional byte on the finish, whereas the substitute phrases are listed as easy character arrays listed elsewhere. The ultimate byte of every censored phrase comprises flag bits that denote if the phrase is whitelisted, allowed in non-strict mode, and which G-rated phrase ought to substitute it. To see this evaluation in additional element, take a look at Eater’s video beneath!