Vintage Height Encoding Height Test Set: A Deep Dive into its Binary-Based Altitude Measurement
0:00:05 Introduction: The video introduces a vintage height test set that uses a binary-based Gillham code, similar to Gray code, for height encoding.
0:00:17 Gillham Code: This encoding system changes only one bit when the height changes by 100 feet.
0:00:22 Transponder Use: The binary coding is used for transponders, with 11 indicators displaying the state of each bit (LSB to MSB - D2).
0:00:37 Input and Power: The unit features an encoder input, a power supply connector, an on/off switch, and a tone that activates above 1000 feet, with a small loudspeaker.
0:00:55 Altitude Display: The altitude is displayed using five Nixie tubes.
0:01:08 Incompatible Cables: The included cables have incompatible connectors (6-pin male) for the unit.
0:01:31 Air Data Computer Connection: The unit is designed to connect to an Air Data Computer or a specific sensor, like the automatic pressure altitude digitizer shown.
0:01:42 Altitude Digitizer: The example digitizer has a limited range of -1,000 to 20,000 feet and uses only nine bits, while the main unit uses 11 bits.
0:02:06 Elliott Air Data Computer Module: A height module for an Elliott Air Data Computer is shown, featuring a digital encoder with a calibration seal.
0:03:08 Internal Components: The video reveals the internal components, including a power supply transformer, Nixie tubes with drivers (8T01B, date code 72), and multiple circuit boards.
0:03:55 Board Analysis: The first board contains a monostable (74121), an unknown part (930), and a DTL Logic (946). Two identical boards have op-amps or comparators (date code 70), with six circuits likely serving as the front end for the 11 input bits.
0:05:14 DTL Logic: Another board features SMD 946 components, indicating DTL logic, along with various logic ICs (date codes 70-72) and obscure parts (N8241A).
0:05:52 Reverse Engineering: The next step is to reverse engineer a section of the last board, which includes an op-amp or comparator and three transistors, to identify the six inputs and corresponding connector pins.
0:06:21 Front End: This section is identified as the front end for one bit.