Serial communication with Arduino using a 7404 – Arduino, ESP8266, ESP32 & Raspberry Pi stuff
digital logic - Why does the output of NOT gate (in a 74LS04 IC) equal to one when the input wire is not connected to anywhere? - Electrical Engineering Stack Exchange
File:7404 Hex Inverters.PNG - Wikimedia Commons
DM7404J National Semiconductor IC TTL Hex Inverter 7404 Ceramic - NOS Qty 2 | eBay
Understanding the 7404 Hex Inverter: Functionality and Applications – HIGH-END FPGA Distributor