Model 14TD reading a punched paper tape

This TD reads both fully punched and chadless tapes.

The outer copper disc is divided into seven sections, and the spinning commutator connects the signal line to each one in sequence as it rotates. The first, the start bit, is always "off". The last, the stop bit, is always on, and is 1.5x the length of the other bits. The five bits in between are connected to switches activated by rods which try to poke up through the paper tape; if there is a hole, that segment is "on" and if not, it's "off." So for each row of holes on the tape, the machine sends a start bit, five data bits, and a stop bit, then advances the tape and repeats. Designed in the 1930s, it is a mechanical implementation of what we would call the transmitter portion of a UART.