Tuesday, October 16, 2018

Looking at power in the AGC and at the DSKY interface


Power within the AGC

The AGC is powered by the main 28V DC bus of the spacecraft. It provides filtering for the 28V and distributes it out to signal conditioning and other interface boxes connecting the AGC to the inertial management unit, telemetry and other systems. Within the AGC, power supplies produce 14V DC and 4V DC. The 14V is needed for the memories, while the logic runs on 4V.

Two different 4V supplies are produced in the AGC. The one connected to most logic modules is called 4SW, because it is switched off when the AGC is put into standby (a very low power mode). The other 4V goes to the few parts of the AGC which must run all the time. For instance, the clock oscillator, divider, and scaler produce timing signals used by the IMU, telemetry and other systems, so it must produce those even when the AGC is in standby. 

DSKY, the visible interface

The DSKY is the portion that was visible to astronauts and the public. It provides a set of glowing numbers, some pushbuttons and caution/warning lights. One DSKY is mounted on the main panel of the Command Module, between the CM pilot and mission commander seats. The other is down in the lower equipment bay of the CM, near the AGC tself and to the optics used to take celestial navigation readings to keep the intertial navigation aligned properly. On the LM, a single DSKY is mounted on the central control panel.

There are three main portions of the DSKY. The bottom 1/3rd has a matrix of pushbuttons, a main block 5 across by 3 down, with two vertical buttons on each side of the main block. The upper left has a set of 12 caution or warning lights, rectangular panels with text on them that would light up in white or yellow. The upper right has an electroluminescent panel that displays three signed five digit numbers on the bottom half, a two digit verb and two digit noun  side by side above that, and a two digit 'program number' displayed on the top.

The electroluminescent section used 250V 800 Hz AC to excite the segments to glow green, at 5300 angstroms. The high voltage was switched through many small relays inside the display, allowing the AGC to use a low DC voltage to switch the high voltage AC to the display elements. It took 37 relays just to power one of the signed five digit numbers.

The caution and warning lights were ordinary 5V DC incandescent bulbs, driven through relays that in turn were powered by the AGC. Status lights had a white background while caution/warning lights glowed in yellow.

The main keyboard section had the 15 main buttons, providing +, -, the ten digits, Proceed, Clear and Key Release. The two vertical buttons on the left are Verb and Noun. The two vertical buttons on the right are Enter and Reset. The 19 buttons are encoded in a 5 digit keystroke value and monitored by the AGC.

The keyboards were back-lit by 110V AC 400 Hz lights, making use of the standard AC bus of the spacecraft. 

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