Today (2017) this device would be manufactured using maybe a single micro-controller and would be very simple. I am sure that even nowadays many astronauts would like to have a similar device to communicate with the guidance computer at least as a reserve device in case of some problem with the modern touch screens and high resolution displays. Its small size, simplicity and integration with the Apollo software and hardware will keep this device popular in the future also. Most of this material is from /1/. This text and drawings /1/ did have some differences with other documents but is anyway useful in its detail.
The AGC (and DSKY) was designed at the MIT Instrumentation Laboratory under Charles Stark Draper, with hardware design led by Eldon C. Hall. Early architectural work came from J.H. Laning Jr., Albert Hopkins, Richard Battin, Ramon Alonso, and Hugh Blair-Smith. The flight hardware was fabricated by Raytheon, whose Herb Thaler was also on the architectural team.
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| Eldon C. Hall |
Most of these people can be seen in the following film
YouTube video: "Computer for Apollo, MIT Science Reporter Film"]
High resolution images to this article are available here.
"The LM DSKY is located below the center panels of the cockpit display and control panels.
The DSKY (figure 30) consists of a keyboard: a relay matrix with associated decoding circuits, displays, mode and caution circuits; and a power supply. The keyboard, which contains several numerical, sign, and other control keys, allows the astronaut to communicate with the LGC. The inputs from the keyboard are entered into an input channel and processed by the LGC.
[DSKY keyboard and display operate separately. The operation of the display is shown in the above figure. By writing to the output channel 0010 (octal) AGC can write to a single pair of digits at one time. To update the whole display all pairs must be visited. Relay matrix column data sets the information which segments should be illuminated of the selected digit pair. The row select is generated from the upper part of the written word by the decoder.
Once a row is selected by the decoder the associated row line voltage is pulled down via diodes so that any relays connected to that line will be energized by any data written to the columns Since the relays are latching there are two coils in each relay. One coil will set it to "0" (off) and one to "1" (on). Both voltages are generated from the single bit information. Once settled the relay does not need any additional energy and will keep its state. Only one pair of digits are connected to a single row select line. So to address about 24 digits in the DSKY display about 12 lines are required. Due to the mechanical matter of the relays (long settle time) the update rate cannot be very fast and so the update operation can be visually seen and heard on the DSKY display. A feature that makes DSKY so unique among displays.]
YouTube video about DSKY update rate: "Apollo command module computer"
The inputs entered from the keyboard, as well as other information, appear on the displays after processing by program. The display of information is accomplished through the relay matrix. A unique code for the characters to be displayed is formed by fifteen bits from output channel 10 (octal) in the LGC. Bits 12 through 15 are decoded by the decoding circuits, and, along with bits 1 through 11, energize specific relays in the matrix which causes the appropriate characters to illuminate. The information displayed is the result of a keycode punched in by the astronaut, or is computer-controlled information. The display characters are formed by electroluminescent segments which are energized by a voltage from the power supply routed through relay contacts. Specific inputs from the PGNCS are also applied, through the LGC to certain relays in the matrix through output channel 10 of the LGC. The resulting relay-controlled outputs are caution signals to the PGNCS. The mode and caution circuits accept direct input signals from channels 1l, 12, and 13, without being decoded. The resulting outputs can give an indication to the astronaut on the DSKY and route the output signal to the PGNCS and spacecraft."
The LGC has one DSKY located on the front wall of the LEM cabin. The CMC has two associated DSKY's - one is mounted on the main display and control panel (main DSKY) in the lower equipment bay of the command module, the second is mounted on the navigation display and control panel (navigation DSKY). All three DSKY’s are electrically identical. As such, the two in the command module are interchangeable.
1 DSKY Functional Description.
The DSKY (figure 222) consists of a keyboard, power supply, decoder, relay matrix, status and caution circuits, and displays
The keyboard contains the key controls with which the astronaut operates the DSKY. Each of the key controls is illuminated by 115 VAC at 400 CPS. Inputs to the computer initiated from the keyboard are processed by the program. The results are supplied to either the decoder and relay matrix or the status and caution circuits for display. Each key when pressed, with the exception of STBY, will produce a 5 bit code. The keycode is entered into the computer and initiates an interrupt to allow the data to be accepted. The key reset signal (+28 volts) is generated each time a key is released, the signal conditions the computer to accept another keycode. The reset code and reset signal (+28 volts) is used when the operator wishes to extinguish certain display indicators. It also allows a check to determine whether a particular indication is transient or permanent. The clear code is used when the operator wishes to clear displayed sign and digit information. Key release turns the control of displaying information on the DSKY over to the computer. The standby signal (+28 volts) initiates placing the computer into the standby mode and into the operate mode when pressed a second time.
The power supply utilizes +28 volts and +14 volts from the computer power supply and an 800-CPS sync signal from the timer to generate a 250 VAC, 800 CPS display voltage. The display voltage is applied to the displays through the relay matrix and status and caution circuits.
The decoder receives a four bit relay word (bits 12 through 15) from channel 10 in the computer. The decoded relay word, in conjunction with relay bits 1 through 11 from channel 10, energizes specific relays in the matrix. The relays are energized by the coincidence of two signals: a selection signal from the diode matrix in the decoder which produces a row selection signal and relay bits which produce column selection signals. Relay selection allows the display voltage (250 VAC) from the DSKY power supply to be routed to the proper sign and digit indicators. Relay selection also allows the alarm common (0 VDC) or +5 volts from the PGNCS system or the spacecraft to be routed through the relay to one of the following: PGNCS system (caution signals), the spacecraft (caution signals), or proper status and caution indicators. The PGNCS caution signals from the relay matrix, represented by 0 VDC, are PGNS CAUTION, TRACKER, and GIMBAL LOCK. The status and caution indicators, illuminated by the +5 volts are: PROG, TRACKER, GIMBAL LOCK, and NO ATT. All relays associated with the relay matrix are latching t3cpe relays.
The status and caution circuits receive all status and caution signals from the computer. Each signal is applied to a driver circuit and associated relay. When a relay is energized, it allows the voltage from the DSKY power supply (250 VAC), or +5 volts or 0 VDC from the PGNCS or spacecraft to be routed to the proper display indicators or equipment. The voltage from the power supply is routed through a relay to the computer activity indicator (COMP ACTY). The +5 volts is routed through relays to the following status and caution indicators: UPLINK ACTY, RESTART, OPR ERR, KEY REL, and TEMP.
The LGC status and caution signals, represented by 0 VDC or an open circuit, are ISS WARNING, STBY, LRDR POS CMD, RR AUTO TRACK ENABLE, LGC WARNING, and PGNS CAUTION.
In the CMC, the status and caution signals, represented by 0 VDC or an open circuit, are ISS WARNING, STBY, SIVB INJ, SEQ START, SIVB CUT-OFF, CMC WARNING, and PGNS - G/N CAUTION.
All relays associated with the status and caution circuits are non-latching.
The displays consist of sign and digital (operational and data display) and status and caution indicators. The sign and digital indicators allow the astronaut to observe the data entered or requested from the keyboard. The status and caution indicators present an indication of any variance from certain normal operations.
2 DSKY Detailed Description.
The DSKY consists of a keyboard and display section, decoder, relay matrix, status and caution circuits, and power supply.
2.1 Keyboard and Display.
The keyboard section (figure 223) contains 10 digit keys (0 through 9) and 9 operational keys (VERB, NOUN, CLR, PRO, KEY REL, ENTR, RESET, +, and -).
Except for operational key PRO, all of the keys, when pressed, generate different five-bit binary keycode which is applied to an input channel of the input-output section. In the LGC, the keycode is applied to channel 15 of the input/output section. In the CMC, the keycode from the main DSKY is applied to channel 15: the keycode from the navigation DSKY is applied to channel 16. The keycodes are shown beside their respective keys on figure 223. The PRO key, when pressed, generates +28 volts through key contacts to the standby circuits in the computer. This key is also used to allow the program to proceed without data in lieu of entering VERB 33. Each of the 18 keys is illuminated by 115 VAC, 400 CPS from the spacecraft.
The key contacts (figure 224) are connected in series to ensure that only one keycode will be produced at one time.
The binary keycode is produced by applying +28 volts through the key contacts to a diode network. The keycode initiates a program interruption (KEYRUPT) in the computer. When a key is released, signal KEYRST resets the input channel, thus clearing it for the acceptance of another keycode. A key must be released before another key is pressed to have information processed by the computer.
[Since DSKY keyboard is using toggle switch buttons with NO (Normally Open) and NC (Normally Closed) contacts it can tell to the computer that any button is pressed or all buttons are not pressed. That is done so that normally all buttons are connected via their NC contacts in series to the KEYRST line (which is high all the time when nothing is pressed). But when something is pressed the line KEYRST drops down and again when it is released the KEYRST line return to high state. The series connection also prevents any double key mixed signals to be sent to the computer.]
[The diode matrix schematic (figure 224.) above is a bit alone hanging and we would like to know how are the keycode lines actually connected to the computer. That can be seen in the previous DSKY article here and repeated in the above figure. All keycode diode lines and buttons are connected using "D" circuits which are low pass filters and trigger circuits. Lower energy spikes will not have enough energy to charge the low pass filter capacitor in the input circuit to so high value that the input port would trigger to high state. But when a key is pressed and it connects the 20 k charging resistor to the 28 V line and it is kept there at least about 10 milliseconds there will be enough potential to set the signal input line to value "one". In that way the low pass filter removes key contact bounces and spikes in the long lines to the computer. Additionally the required KEYRST signal to follow any valid keycode will remove additional key bounces, disturbances and false key presses. Building a keyboard this way makes it very reliable.]
The display section (figure 223) contains 24 digit displays (21 for numerical and 3 for sign) and 15 indicators (spare included). The 24 digit displays (DSl except COMP ACTY) and 15 indicators (DS2 plus COMP ACTY) are arranged as shown in figure 223. The displays and indicators are luminescent-coated-glass assemblies which glow when a voltage is applied to the coating. The displays (digit and sign) are segmented, and a display voltage of 250 VAC from the DSKY power supply is applied to each segment through contacts in the relay matrix. The indicators are made in one piece. Except for COMP ACTY which receives 250 VAC, all the indicators receive a display voltage of +5 volts from the spacecraft through relay contacts. The brightness of certain displays (digit, sign, and COMP ACTY) varies as a function of the voltage and frequency applied to the coating. The voltage can be varied using the brightness control on the astronauts control panel in the PGNCS.
The standard procedure for communicating with the computer is to press seven keys in the following sequence: VERB-DIGIT-DIGIT, NOUN-DIGIT-DIGIT, and ENTR.
Pressing the VERB key on the keyboard clears the VERB displays on the display and indicators. The two digits punched in next are interpreted as a VERB code and displayed in the VERB section. This same operation occurs using the NOUN and two digits. The operation of the VERB-NOUN code is not initiated in the computer until key ENTR is pressed. If an error is noticed in either the VERB or NOUN before ENTR is pressed, it may be corrected by repunching either the VERB or NOUN key and the correct code.
If the VERB-NOUN combination punched in requires additional data to be furnished by the operator, the VERB and NOUN displays flash once every 1.5 seconds after the ENTR key has been pressed. The flashing indicates that the operator should punch-in the required data on the keyboard. After punching in the required data and the ENTR key, the flashing ceases.
Octal and decimal data words can be punched in. The computer assumes that an octal data word will be entered if a sign key (+ or -) is not pressed. If digit key 8 or 9 is pressed while loading an octal data word, indicator OPR ERR flashes once every 1.5 seconds. Whenever key (+) or key (-) is pressed, the corresponding signal is displayed and the computer assumes that a decimal word is to be entered. If an error is noticed while punching in either octal or decimal data, the CLR key can be pressed and the correct entry can be made if the ENTR key has not been pressed. All data words entered must be either octal or decimal; combinations of octal and decimal are not permitted.
To eliminate the flashing of indicator OPR ERR due to irregular keyboard entrys, key RSET must be pressed. In addition to the keycode, a hard wired signal (+28 VDC) is applied to the computer. Both the keycode and hard wire signal extinguish the status indicator OPR ERR as well as the five caution indicators: TEMP, GIMBAL LOCK, PROG, RESTART, and TRACKER. Thus, key RSET may also be used to test for the presence of a continuous caution rather than a transient caution condition.
2.2 Decoder.
The decoder (figure 225) contains four relay word drivers (circuits 002 and 003 make up one driver), a diode matrix, and 12 row select drivers.
The relay word drivers receive bits 15 through 12 of channel 10. Combinations of these 4 bits select 1 of 12 rows of relays in the relay matrix. The 12 code combinations from channel 10, are shown beside their particular row selection number on figure 225. For simplification only the selection of row 1 is discussed. The code for row 1 selection (0001) is inverted in the interface circuits (A25) and applied to DSKY connector J9 as signals CE228 through CE225. To identify row 1, signals CE228 through CE226 are logic one's and signal CE225 is a logic ZERO. A logic ONE shuts transistor Q1 off, which holds transistor Q2 off and allows transistor Q3 to conduct. Therefore, the X outputs of circuits controlled by signals CE228 through CE226 are logic ONE'S, and the Y output of the circuit controlled by signal CE225 is a logic ONE.
The diode matrix receives the 8-bit output from the four relay word drivers. The matrix is wired so each 8-bit input produces a logic ONE on only one output line to the word drivers. For row 1 selection, diode CR53 of modules D2, D3, and D4, and diode CR63 of module D5 must be reverse biased. When these diodes are not conducting, row select driver circuit 004 on module D1 is activated. A current path is provided from +28 volts of the row selection driver voltage source (through transistor Ql, R8 of CKT 004, CR44, R9) to 0 VDC. Thus, parallel transistors Q4 and Q5 conduct and supply 0 VDC, representing row 1 selection, to the relay matrix.
The bottom row of diodes in the diode matrix (CR54 of modules D2 through D5} are used to detect the presence of logic ZERO'S in bits 12 through 15 of channel 10. During normal operation at least one of the four diodes is forward biased and applies 0 VDC to the row selection driver voltage source. This 0 VDC is needed to supply a row selection signal (0 VDC) to the relay matrix as discussed previously. If the four most significant bits of channel 10 are ZERO'S, all four diodes are reverse biased and +28 volts (+28 BC) are applied to the input of the row selection driver voltage source. An input of +28 volts turns transistor Q2 on which in turn keeps transistor Q3 off. With no output from Q3, transistor Ql is held off and the output of transistor Ql is effectively an open circuit. Thus, there is no voltage source for circuit operation of any row selection driver circuit.
The indicator driver module circuits (figure 226) are used in making up the decoder, relay matrix, and status and caution circuits. They are introduced at this time to assist in better understanding the previously mentioned areas. All six indicator driver modules (D1 through D6) are identical and interchangeable.
2.3 Relay Matrix.
The relay matrix (figure 227) consists of 11 relay bit drivers and 12 rows of latching relays.
Each relay bit driver accepts 1 of 11 bits (11 through 1) of channel 10. For simplification only bit 11 (circuit 006 on module D6) is discussed. When bit 11 of channel 10 is a ONE, it is inverted in the interface circuits (A25) and applied to DSKY connector J9 as signal CE224. A ZERO input to circuit 006 turns transistor Q8 on which switches transistor Q9 off. Thus, +28 volts is present on pin 10 (TURN-ON) of the column of relays dealing with the plus and minus sign display. With a row selection signal from the diode matrix (0 VDC) and a column select signal from a relay bit driver (+28 volts), a single relay within the relay matrix is controlled.
[Almost all Block II DSKYs in the Smithsonian Collection have different external sizes, most usually the numbers are about (20.3 x 20.3 x 16.5 cm (8 x 8 x 6 1/2 in.)) or larger. There was also a block I DSKY but it was totally different kind of. This information is from Smithsonian Institute.]
Link to Smithsonian Dskies
All of the relays in the relay matrix control the DSKY displays. Row 12 controls the indicators associated with the status and caution indicators (DS2) and, in addition, supplies a PGNS CAUTION signal to the display and control section of the PGNCS
Table C relates the content of channel 10 to the row and column selected and the digit or indicator display controlled by the individual relay. Five relays are required to display one digit. Relay bit drivers 10 through 6 control the display of one digit and relay bit drivers 5 through 1 control the display of a second digit. Relay bit driver 11 causes the display of a plus or minus sign. The five-bit code necessary to display digits 0 through 9 in any display location is listed in table C1 below.
The relays representing REG3-POS1 of row 1 are used as an example. A logic ONE indicates that the relay is energized. For identification of display locations refer to figure 228.
Energizing the proper relays within the relay matrix (rows 1 through 11) allows approximately 250 VAC from the DSKY power supply to be routed through the relay contacts to the various segments of the electroluminescent digit and sign indicators. Figure 229 illustrates the relays, their codes, and a display coding key.
Energizing a relay in row 12 allows +5 volts from the electrical power system in the spacecraft to be routed through the relay contacts to a status or caution indicator. Relays K16, K17, and K18 are spares. In addition, relays PROG, TRACKER, and GIMBAL LOCK receive the signal alarm common from the spacecraft and, when energized, supply signal PGNS CAUTION to the PGNCS.
2.4 Status and Caution Circuits.
The status and caution circuits for the LGC (figure 230) consist of driver circuits and associated non-latching relays.
For simplification only circuit 008 on module D4 is discussed. When signal ISS WARNING is a logic ZERO it will turn on transistor Q13 and supply +28 volts to associated relay K21. Relay K21 energizes and routes input signal ALARM COMMON through its contacts to the display and control section of the PGNCS as signal ISS WARNING. The driver circuits and relays associated with signals LGC WARNING, TEMP CAUTION, and RESTART also receive signal ALARM COMMON. Signal TEMP CAUTION or RESTART causes the generation of signal PGNS CAUTION which is applied to the PGNCS and also causes +5 volt caution power to be applied to the respective indicators on the DSKY front panel.
The driver circuits and relays associated with signals UPLINK ACTY, OPR ERROR, KEY REL, and STBY will apply, when activated, +5 volt status power to their respective indicators on the DSKY front panel. Indicators OPR ERR and KEY REL flash at a 1.5 CPS ACTY is physically a part of digital indicator DSI. However, electrically it is part of the status circuits. When signal COMP ACTY is present 250 VAC is routed through the relay contacts to its indicator. Circuits dealing with signals RR ENABLE LOC ON, LGC WARNING. LRDR POS CMD, and ISS WARNING do not have visual indications on the front panel of the DSKY.
The verb-noun flash causes the verb-noun indicators to flash by interrupting, at a 1.5 CPS rate, what normally is 250 VAC being applied to the verb-noun relays in the relay matrix.
The status and caution circuits for the CMC are illustrated on figure 231. These circuits are identical in operation to those in the LGC. Several interface differences exist, however. These can be determined by examining the inputs and outputs to the status and caution circuits for the CMC on figure 231.
2.5 Power Supply.
The DSKY power supply (figure 232) utilizes +28 VDC and +14VSW from the computer power supply, and 800 CPS from the timer to generate a display voltage of approximately 250 VAC, 800 CPS.
The power supply contains three transformer-coupled, push-pull amplifiers. The input to the first stage is an 800-CPS square wave varying about a +14 VDC level. The dc level is controlled by the brightness control on the astronauts' control panel. Transformers T1 and T2 step up the voltage applied to their primary windings. The output from the third push-pull stage is applied to saturable reactor L2.
Reactor L2 and its associated circuit regulate the voltage applied to the displays. The displays act as a variable capacitive load that varies as a function of the number of indicators that are on. Changes in the load are reflected back to the control winding of L2 through the full-wave bridge rectifier, CRl through CR4. As the number of indicators which are on increases, the voltage applied to the control winding is increased. An increase in voltage through the control winding drives reactor L2 further into saturation and keeps the output relatively constant. If the load decreases, the voltage through the control winding decreases, and L2 is less-saturated."
Additionally to these parts there was other systems like the explosive devices, other displays and controls, electrical power supply, environmental control, lighting, communications, main propulsion, reaction control, instrumentation, etc. and of course the abort guidance system (AGS) outside primary (MIT). In the above diagram we have the following block names.
All together LM had 12 subsystems (see here for additional details).
RESOURCES
/1/ APOLLO LUNAR EXCURSION MODULE PRIMARY GUIDANCE, NAVIGATION, AND CONTROL SYSTEM MANUAL VOLUME II OF II - PREPARED FOR NATIONAL AERONAUTICS AND SPACE ADMINISTRATION, MANNED SPACECRAFT CENTER BY DELCO ELECTRONICS, DIVISION OF GENERAL MOTORS, MILWAUKEE, WISCONSIN 53201, NASA CONTRACT NAS 9-497, 1 FEB 1966 - ND-1021042, REVISION AK, INITIAL TDRR 26432, TYPE II, APPROVED BY NASA - link to https://archive.org/details/acelectroniclmma00acel_0
/2/ High resolution images to this article are available here.
/3/ Smithsonian Collections
High resolution images to this article are available here.
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| Figure 1. DSKY was located in front of astronauts in LM and it was connected to the LGC which was located behind them. |
LM COMPUTER DISPLAY AND KEYBOARD, DSKY /1/
"The LM DSKY is located below the center panels of the cockpit display and control panels.
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| Figure 30. General DSKY Block Diagram. |
The DSKY (figure 30) consists of a keyboard: a relay matrix with associated decoding circuits, displays, mode and caution circuits; and a power supply. The keyboard, which contains several numerical, sign, and other control keys, allows the astronaut to communicate with the LGC. The inputs from the keyboard are entered into an input channel and processed by the LGC.
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| Figure 2. Operation of the display. Latching relays serve as high voltage drivers and memory at the same time. |
[DSKY keyboard and display operate separately. The operation of the display is shown in the above figure. By writing to the output channel 0010 (octal) AGC can write to a single pair of digits at one time. To update the whole display all pairs must be visited. Relay matrix column data sets the information which segments should be illuminated of the selected digit pair. The row select is generated from the upper part of the written word by the decoder.
Once a row is selected by the decoder the associated row line voltage is pulled down via diodes so that any relays connected to that line will be energized by any data written to the columns Since the relays are latching there are two coils in each relay. One coil will set it to "0" (off) and one to "1" (on). Both voltages are generated from the single bit information. Once settled the relay does not need any additional energy and will keep its state. Only one pair of digits are connected to a single row select line. So to address about 24 digits in the DSKY display about 12 lines are required. Due to the mechanical matter of the relays (long settle time) the update rate cannot be very fast and so the update operation can be visually seen and heard on the DSKY display. A feature that makes DSKY so unique among displays.]
YouTube video about DSKY update rate: "Apollo command module computer"
The inputs entered from the keyboard, as well as other information, appear on the displays after processing by program. The display of information is accomplished through the relay matrix. A unique code for the characters to be displayed is formed by fifteen bits from output channel 10 (octal) in the LGC. Bits 12 through 15 are decoded by the decoding circuits, and, along with bits 1 through 11, energize specific relays in the matrix which causes the appropriate characters to illuminate. The information displayed is the result of a keycode punched in by the astronaut, or is computer-controlled information. The display characters are formed by electroluminescent segments which are energized by a voltage from the power supply routed through relay contacts. Specific inputs from the PGNCS are also applied, through the LGC to certain relays in the matrix through output channel 10 of the LGC. The resulting relay-controlled outputs are caution signals to the PGNCS. The mode and caution circuits accept direct input signals from channels 1l, 12, and 13, without being decoded. The resulting outputs can give an indication to the astronaut on the DSKY and route the output signal to the PGNCS and spacecraft."
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| Figure 3. Apollo Guidance Computer (AGC or LGC) and its display keyboard device DSKY. |
DISPLAY AND KEYBOARD (DSKY) /1/
"The DSKY provides a means of communicating with the computer. It allows the operator to load information into the computer, request information, initiate various programs stored in memory, and perform tests on the computer and other subsystems of the PGNCS system. The DSKY also provides an indication of status and caution changes which may occur within the computer. |
| Figure 4. A miniature latching relay. |
The LGC has one DSKY located on the front wall of the LEM cabin. The CMC has two associated DSKY's - one is mounted on the main display and control panel (main DSKY) in the lower equipment bay of the command module, the second is mounted on the navigation display and control panel (navigation DSKY). All three DSKY’s are electrically identical. As such, the two in the command module are interchangeable.
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| Figure 5. Relay dimensions. |
1 DSKY Functional Description.
The DSKY (figure 222) consists of a keyboard, power supply, decoder, relay matrix, status and caution circuits, and displays
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| Figure 222. DSKY Functional Diagram |
The keyboard contains the key controls with which the astronaut operates the DSKY. Each of the key controls is illuminated by 115 VAC at 400 CPS. Inputs to the computer initiated from the keyboard are processed by the program. The results are supplied to either the decoder and relay matrix or the status and caution circuits for display. Each key when pressed, with the exception of STBY, will produce a 5 bit code. The keycode is entered into the computer and initiates an interrupt to allow the data to be accepted. The key reset signal (+28 volts) is generated each time a key is released, the signal conditions the computer to accept another keycode. The reset code and reset signal (+28 volts) is used when the operator wishes to extinguish certain display indicators. It also allows a check to determine whether a particular indication is transient or permanent. The clear code is used when the operator wishes to clear displayed sign and digit information. Key release turns the control of displaying information on the DSKY over to the computer. The standby signal (+28 volts) initiates placing the computer into the standby mode and into the operate mode when pressed a second time.
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| Figure 6. DSKY external parts. |
The power supply utilizes +28 volts and +14 volts from the computer power supply and an 800-CPS sync signal from the timer to generate a 250 VAC, 800 CPS display voltage. The display voltage is applied to the displays through the relay matrix and status and caution circuits.
The decoder receives a four bit relay word (bits 12 through 15) from channel 10 in the computer. The decoded relay word, in conjunction with relay bits 1 through 11 from channel 10, energizes specific relays in the matrix. The relays are energized by the coincidence of two signals: a selection signal from the diode matrix in the decoder which produces a row selection signal and relay bits which produce column selection signals. Relay selection allows the display voltage (250 VAC) from the DSKY power supply to be routed to the proper sign and digit indicators. Relay selection also allows the alarm common (0 VDC) or +5 volts from the PGNCS system or the spacecraft to be routed through the relay to one of the following: PGNCS system (caution signals), the spacecraft (caution signals), or proper status and caution indicators. The PGNCS caution signals from the relay matrix, represented by 0 VDC, are PGNS CAUTION, TRACKER, and GIMBAL LOCK. The status and caution indicators, illuminated by the +5 volts are: PROG, TRACKER, GIMBAL LOCK, and NO ATT. All relays associated with the relay matrix are latching t3cpe relays.
The status and caution circuits receive all status and caution signals from the computer. Each signal is applied to a driver circuit and associated relay. When a relay is energized, it allows the voltage from the DSKY power supply (250 VAC), or +5 volts or 0 VDC from the PGNCS or spacecraft to be routed to the proper display indicators or equipment. The voltage from the power supply is routed through a relay to the computer activity indicator (COMP ACTY). The +5 volts is routed through relays to the following status and caution indicators: UPLINK ACTY, RESTART, OPR ERR, KEY REL, and TEMP.
The LGC status and caution signals, represented by 0 VDC or an open circuit, are ISS WARNING, STBY, LRDR POS CMD, RR AUTO TRACK ENABLE, LGC WARNING, and PGNS CAUTION.
In the CMC, the status and caution signals, represented by 0 VDC or an open circuit, are ISS WARNING, STBY, SIVB INJ, SEQ START, SIVB CUT-OFF, CMC WARNING, and PGNS - G/N CAUTION.
All relays associated with the status and caution circuits are non-latching.
The displays consist of sign and digital (operational and data display) and status and caution indicators. The sign and digital indicators allow the astronaut to observe the data entered or requested from the keyboard. The status and caution indicators present an indication of any variance from certain normal operations.
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| Figure 7. DSKY front face. The larger DSKY (24.1 x 25.4 x 15.2cm or 9 1/2 x 10 x 6 in.) in Smithsonian Collection. Possible just used in tests by NASA. |
2 DSKY Detailed Description.
The DSKY consists of a keyboard and display section, decoder, relay matrix, status and caution circuits, and power supply.
2.1 Keyboard and Display.
The keyboard section (figure 223) contains 10 digit keys (0 through 9) and 9 operational keys (VERB, NOUN, CLR, PRO, KEY REL, ENTR, RESET, +, and -).
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| Figure 223. Keyboard and display front panel. |
Except for operational key PRO, all of the keys, when pressed, generate different five-bit binary keycode which is applied to an input channel of the input-output section. In the LGC, the keycode is applied to channel 15 of the input/output section. In the CMC, the keycode from the main DSKY is applied to channel 15: the keycode from the navigation DSKY is applied to channel 16. The keycodes are shown beside their respective keys on figure 223. The PRO key, when pressed, generates +28 volts through key contacts to the standby circuits in the computer. This key is also used to allow the program to proceed without data in lieu of entering VERB 33. Each of the 18 keys is illuminated by 115 VAC, 400 CPS from the spacecraft.
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| Figure 8. Meaning of various parts in DSKY. |
The key contacts (figure 224) are connected in series to ensure that only one keycode will be produced at one time.
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| Figure 224. DSKY Keyboard Schematic Diagram. |
The binary keycode is produced by applying +28 volts through the key contacts to a diode network. The keycode initiates a program interruption (KEYRUPT) in the computer. When a key is released, signal KEYRST resets the input channel, thus clearing it for the acceptance of another keycode. A key must be released before another key is pressed to have information processed by the computer.
[Since DSKY keyboard is using toggle switch buttons with NO (Normally Open) and NC (Normally Closed) contacts it can tell to the computer that any button is pressed or all buttons are not pressed. That is done so that normally all buttons are connected via their NC contacts in series to the KEYRST line (which is high all the time when nothing is pressed). But when something is pressed the line KEYRST drops down and again when it is released the KEYRST line return to high state. The series connection also prevents any double key mixed signals to be sent to the computer.]
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| Figure 9. "D" circuits after the keyboard in the computer inputs take care of removing false key presses (bounces) and other disturbances. |
[The diode matrix schematic (figure 224.) above is a bit alone hanging and we would like to know how are the keycode lines actually connected to the computer. That can be seen in the previous DSKY article here and repeated in the above figure. All keycode diode lines and buttons are connected using "D" circuits which are low pass filters and trigger circuits. Lower energy spikes will not have enough energy to charge the low pass filter capacitor in the input circuit to so high value that the input port would trigger to high state. But when a key is pressed and it connects the 20 k charging resistor to the 28 V line and it is kept there at least about 10 milliseconds there will be enough potential to set the signal input line to value "one". In that way the low pass filter removes key contact bounces and spikes in the long lines to the computer. Additionally the required KEYRST signal to follow any valid keycode will remove additional key bounces, disturbances and false key presses. Building a keyboard this way makes it very reliable.]
The display section (figure 223) contains 24 digit displays (21 for numerical and 3 for sign) and 15 indicators (spare included). The 24 digit displays (DSl except COMP ACTY) and 15 indicators (DS2 plus COMP ACTY) are arranged as shown in figure 223. The displays and indicators are luminescent-coated-glass assemblies which glow when a voltage is applied to the coating. The displays (digit and sign) are segmented, and a display voltage of 250 VAC from the DSKY power supply is applied to each segment through contacts in the relay matrix. The indicators are made in one piece. Except for COMP ACTY which receives 250 VAC, all the indicators receive a display voltage of +5 volts from the spacecraft through relay contacts. The brightness of certain displays (digit, sign, and COMP ACTY) varies as a function of the voltage and frequency applied to the coating. The voltage can be varied using the brightness control on the astronauts control panel in the PGNCS.
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| Figure 10. DSKY back face. |
The standard procedure for communicating with the computer is to press seven keys in the following sequence: VERB-DIGIT-DIGIT, NOUN-DIGIT-DIGIT, and ENTR.
Pressing the VERB key on the keyboard clears the VERB displays on the display and indicators. The two digits punched in next are interpreted as a VERB code and displayed in the VERB section. This same operation occurs using the NOUN and two digits. The operation of the VERB-NOUN code is not initiated in the computer until key ENTR is pressed. If an error is noticed in either the VERB or NOUN before ENTR is pressed, it may be corrected by repunching either the VERB or NOUN key and the correct code.
If the VERB-NOUN combination punched in requires additional data to be furnished by the operator, the VERB and NOUN displays flash once every 1.5 seconds after the ENTR key has been pressed. The flashing indicates that the operator should punch-in the required data on the keyboard. After punching in the required data and the ENTR key, the flashing ceases.
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| Figure 11. Inside DSKY. |
Octal and decimal data words can be punched in. The computer assumes that an octal data word will be entered if a sign key (+ or -) is not pressed. If digit key 8 or 9 is pressed while loading an octal data word, indicator OPR ERR flashes once every 1.5 seconds. Whenever key (+) or key (-) is pressed, the corresponding signal is displayed and the computer assumes that a decimal word is to be entered. If an error is noticed while punching in either octal or decimal data, the CLR key can be pressed and the correct entry can be made if the ENTR key has not been pressed. All data words entered must be either octal or decimal; combinations of octal and decimal are not permitted.
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| Figure 12. Inside DSKY. |
To eliminate the flashing of indicator OPR ERR due to irregular keyboard entrys, key RSET must be pressed. In addition to the keycode, a hard wired signal (+28 VDC) is applied to the computer. Both the keycode and hard wire signal extinguish the status indicator OPR ERR as well as the five caution indicators: TEMP, GIMBAL LOCK, PROG, RESTART, and TRACKER. Thus, key RSET may also be used to test for the presence of a continuous caution rather than a transient caution condition.
2.2 Decoder.
The decoder (figure 225) contains four relay word drivers (circuits 002 and 003 make up one driver), a diode matrix, and 12 row select drivers.
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| Figure 225. DSKY Decoder Schematic Diagram. |
The relay word drivers receive bits 15 through 12 of channel 10. Combinations of these 4 bits select 1 of 12 rows of relays in the relay matrix. The 12 code combinations from channel 10, are shown beside their particular row selection number on figure 225. For simplification only the selection of row 1 is discussed. The code for row 1 selection (0001) is inverted in the interface circuits (A25) and applied to DSKY connector J9 as signals CE228 through CE225. To identify row 1, signals CE228 through CE226 are logic one's and signal CE225 is a logic ZERO. A logic ONE shuts transistor Q1 off, which holds transistor Q2 off and allows transistor Q3 to conduct. Therefore, the X outputs of circuits controlled by signals CE228 through CE226 are logic ONE'S, and the Y output of the circuit controlled by signal CE225 is a logic ONE.
The diode matrix receives the 8-bit output from the four relay word drivers. The matrix is wired so each 8-bit input produces a logic ONE on only one output line to the word drivers. For row 1 selection, diode CR53 of modules D2, D3, and D4, and diode CR63 of module D5 must be reverse biased. When these diodes are not conducting, row select driver circuit 004 on module D1 is activated. A current path is provided from +28 volts of the row selection driver voltage source (through transistor Ql, R8 of CKT 004, CR44, R9) to 0 VDC. Thus, parallel transistors Q4 and Q5 conduct and supply 0 VDC, representing row 1 selection, to the relay matrix.
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| Figure 13. DSKY bottom. |
The bottom row of diodes in the diode matrix (CR54 of modules D2 through D5} are used to detect the presence of logic ZERO'S in bits 12 through 15 of channel 10. During normal operation at least one of the four diodes is forward biased and applies 0 VDC to the row selection driver voltage source. This 0 VDC is needed to supply a row selection signal (0 VDC) to the relay matrix as discussed previously. If the four most significant bits of channel 10 are ZERO'S, all four diodes are reverse biased and +28 volts (+28 BC) are applied to the input of the row selection driver voltage source. An input of +28 volts turns transistor Q2 on which in turn keeps transistor Q3 off. With no output from Q3, transistor Ql is held off and the output of transistor Ql is effectively an open circuit. Thus, there is no voltage source for circuit operation of any row selection driver circuit.
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| Figure 226. DSKY Indicator Driver Modules (D1-D6). |
The indicator driver module circuits (figure 226) are used in making up the decoder, relay matrix, and status and caution circuits. They are introduced at this time to assist in better understanding the previously mentioned areas. All six indicator driver modules (D1 through D6) are identical and interchangeable.
2.3 Relay Matrix.
The relay matrix (figure 227) consists of 11 relay bit drivers and 12 rows of latching relays.
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| Figure 227. DSKY Relay Matrix Schematic Diagram. |
Each relay bit driver accepts 1 of 11 bits (11 through 1) of channel 10. For simplification only bit 11 (circuit 006 on module D6) is discussed. When bit 11 of channel 10 is a ONE, it is inverted in the interface circuits (A25) and applied to DSKY connector J9 as signal CE224. A ZERO input to circuit 006 turns transistor Q8 on which switches transistor Q9 off. Thus, +28 volts is present on pin 10 (TURN-ON) of the column of relays dealing with the plus and minus sign display. With a row selection signal from the diode matrix (0 VDC) and a column select signal from a relay bit driver (+28 volts), a single relay within the relay matrix is controlled.
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| Figure 14. Another picture of DSKY. |
[Almost all Block II DSKYs in the Smithsonian Collection have different external sizes, most usually the numbers are about (20.3 x 20.3 x 16.5 cm (8 x 8 x 6 1/2 in.)) or larger. There was also a block I DSKY but it was totally different kind of. This information is from Smithsonian Institute.]
Link to Smithsonian Dskies
All of the relays in the relay matrix control the DSKY displays. Row 12 controls the indicators associated with the status and caution indicators (DS2) and, in addition, supplies a PGNS CAUTION signal to the display and control section of the PGNCS
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| Table C. Relay Matrix Codes. |
Table C relates the content of channel 10 to the row and column selected and the digit or indicator display controlled by the individual relay. Five relays are required to display one digit. Relay bit drivers 10 through 6 control the display of one digit and relay bit drivers 5 through 1 control the display of a second digit. Relay bit driver 11 causes the display of a plus or minus sign. The five-bit code necessary to display digits 0 through 9 in any display location is listed in table C1 below.
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| Table C1. Display Segment Digit Codes. |
The relays representing REG3-POS1 of row 1 are used as an example. A logic ONE indicates that the relay is energized. For identification of display locations refer to figure 228.
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| Figure 228. DSKY Display Locations. |
Energizing the proper relays within the relay matrix (rows 1 through 11) allows approximately 250 VAC from the DSKY power supply to be routed through the relay contacts to the various segments of the electroluminescent digit and sign indicators. Figure 229 illustrates the relays, their codes, and a display coding key.
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| Figure 229. DSKY Relay Matrix Signal Flow Schematic Diagram. |
Energizing a relay in row 12 allows +5 volts from the electrical power system in the spacecraft to be routed through the relay contacts to a status or caution indicator. Relays K16, K17, and K18 are spares. In addition, relays PROG, TRACKER, and GIMBAL LOCK receive the signal alarm common from the spacecraft and, when energized, supply signal PGNS CAUTION to the PGNCS.
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| Figure 15. Early "Block I" DSKY design. It was never flown. |
2.4 Status and Caution Circuits.
The status and caution circuits for the LGC (figure 230) consist of driver circuits and associated non-latching relays.
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| Figure 230. Status and Caution Circuit Schematic Diagram. |
For simplification only circuit 008 on module D4 is discussed. When signal ISS WARNING is a logic ZERO it will turn on transistor Q13 and supply +28 volts to associated relay K21. Relay K21 energizes and routes input signal ALARM COMMON through its contacts to the display and control section of the PGNCS as signal ISS WARNING. The driver circuits and relays associated with signals LGC WARNING, TEMP CAUTION, and RESTART also receive signal ALARM COMMON. Signal TEMP CAUTION or RESTART causes the generation of signal PGNS CAUTION which is applied to the PGNCS and also causes +5 volt caution power to be applied to the respective indicators on the DSKY front panel.
The driver circuits and relays associated with signals UPLINK ACTY, OPR ERROR, KEY REL, and STBY will apply, when activated, +5 volt status power to their respective indicators on the DSKY front panel. Indicators OPR ERR and KEY REL flash at a 1.5 CPS ACTY is physically a part of digital indicator DSI. However, electrically it is part of the status circuits. When signal COMP ACTY is present 250 VAC is routed through the relay contacts to its indicator. Circuits dealing with signals RR ENABLE LOC ON, LGC WARNING. LRDR POS CMD, and ISS WARNING do not have visual indications on the front panel of the DSKY.
The verb-noun flash causes the verb-noun indicators to flash by interrupting, at a 1.5 CPS rate, what normally is 250 VAC being applied to the verb-noun relays in the relay matrix.
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| Figure 231. Status and Caution Circuit Schematic Diagram (CMC). |
The status and caution circuits for the CMC are illustrated on figure 231. These circuits are identical in operation to those in the LGC. Several interface differences exist, however. These can be determined by examining the inputs and outputs to the status and caution circuits for the CMC on figure 231.
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| Figure 16. A typical DSKY connection to the computer (CM navigation panel). |
2.5 Power Supply.
The DSKY power supply (figure 232) utilizes +28 VDC and +14VSW from the computer power supply, and 800 CPS from the timer to generate a display voltage of approximately 250 VAC, 800 CPS.
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| Figure 232. DSKY Power Supply Schematic Diagram. |
The power supply contains three transformer-coupled, push-pull amplifiers. The input to the first stage is an 800-CPS square wave varying about a +14 VDC level. The dc level is controlled by the brightness control on the astronauts' control panel. Transformers T1 and T2 step up the voltage applied to their primary windings. The output from the third push-pull stage is applied to saturable reactor L2.
Reactor L2 and its associated circuit regulate the voltage applied to the displays. The displays act as a variable capacitive load that varies as a function of the number of indicators that are on. Changes in the load are reflected back to the control winding of L2 through the full-wave bridge rectifier, CRl through CR4. As the number of indicators which are on increases, the voltage applied to the control winding is increased. An increase in voltage through the control winding drives reactor L2 further into saturation and keeps the output relatively constant. If the load decreases, the voltage through the control winding decreases, and L2 is less-saturated."
LM DSKY in PGNCS (1966)
If we separate the PGNCS (Primary Guidance, Navigation and Control Subsection) from the overall LM Control due to the fact that it was designed by the MIT Instrumentation Lab we can show the following block diagram about the LM systems and how DSKY was situated there. |
| Figure 17. PGNCS Block Diagram (1966) |
Additionally to these parts there was other systems like the explosive devices, other displays and controls, electrical power supply, environmental control, lighting, communications, main propulsion, reaction control, instrumentation, etc. and of course the abort guidance system (AGS) outside primary (MIT). In the above diagram we have the following block names.
- AOT - Alignment Optical Telescope
- LR - Landing Radar
- RR - Rendezvous Radar
- CDU - Coupling Data Unit
- DSKY - (AGC) Display and Keyboard
- LGC - LM Guidance Computer (or AGC)
- PTA - Pulse Torque Assembly
- IMU - Inertial Measurement Unit
- PSA - Power Servo Assembly
- OSS - Optical Subsystem
- ISS - Inertial Subsystem
- RS - Radar Subsystem
All together LM had 12 subsystems (see here for additional details).
RESOURCES
/1/ APOLLO LUNAR EXCURSION MODULE PRIMARY GUIDANCE, NAVIGATION, AND CONTROL SYSTEM MANUAL VOLUME II OF II - PREPARED FOR NATIONAL AERONAUTICS AND SPACE ADMINISTRATION, MANNED SPACECRAFT CENTER BY DELCO ELECTRONICS, DIVISION OF GENERAL MOTORS, MILWAUKEE, WISCONSIN 53201, NASA CONTRACT NAS 9-497, 1 FEB 1966 - ND-1021042, REVISION AK, INITIAL TDRR 26432, TYPE II, APPROVED BY NASA - link to https://archive.org/details/acelectroniclmma00acel_0
/2/ High resolution images to this article are available here.
/3/ Smithsonian Collections
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