Friday, November 2, 2018

DSKY substitute as complete as I could get it before flying to work on AGC


Final construction and testing of the DSKY substitute

I finally finished building all the input interface boards that will safely and compatibly hook the Apollo Guidance Computer outputs based on 28V logic levels with the Arduino Mega 2560 driving the DSKY substitute.

This took half of the morning to wrap up. Twenty four components and ten wires are soldered on the board, which has no traces so the component leads have to bend over to form connections. I then had to inspect all of them for shorts or other errors.

Fifteen of the input circuits hook directly to Arduino input pins. Another eight input circuits are hooked to an I/O expander board on the I2C chain. All eight of the output circuits run through an 8 channel relay board that makes use of my output interface board.

I finished up the wiring of the second 8 channel relay board, which is used to interrupt the cathodes of the 7-segment displays and LEDs to make them flash. A small board gates a 1.5Hz signal through to the relay triggers when the control signal from the AGC is on. The relay clicks on and off to darken the displays.

I am having some difficulties getting the solid wire to hold in the relay board - the design of the connectors are a bit rickety. I tried folding the wire in a U shape, hoping that the two bits of wire would provide a flatter surface for the connector to hold. That did the trick.

The only displays that flash are Operator Error and Key Release caution lights, as well as the four digits of the Verb and Noun displays.That requires six of the eight relays on the board to interrupt their cathodes.

I struggled to find a way to mount the main breadboard panel with the displays and lights  raised off the tabletop, to allow all the support boards and wires to be tucked under or made less visible. Perhaps I could tilt it vertically to the same orientation as a real DSKY, I thought. The keyboard should be at the same level as the display and stationed appropriately.

Cable ties were judiciously applied to neaten up the rats nest of wires between all the boards and modules of this prototype. Transporting this safely will be a major concern. My carry on bag will hold this and a few other fragile items; my laptop and all my other personal items will be wedged into a small 'personal bag'.

All the connections from the myriad of boards and breadboards came to a prototype shield and were soldered in place. Trying to align perhaps 70 pins across different headers to all slide into the female connector was quite challenging with all the wires soldered in place on the shield.

The shield was finally inserted over the Arduino and power was applied. Normally the DSKY comes up with blanks in all the displays and the caution and warning lights are extinguished. For the first tests, I put in some dummy values just to verify that the circuitry is working.

I verified I had fixed the bug that kept the keyboard scan routine from emitting any further keycodes after the first. There is a hardware issue with detection of keypresses in row 3 of the left keypad, something I will chase down and correct.

I did see values displaying and the relays working, although there is a lot of functionality I can't test without the driver since this code is watching 23 input lines and acting on them. These lines are unpowered because I didn't hook the input interface boards up to 28V for this test, meaning the input lines were floating. With power, they would either sit at 0 or 5V depending on the input wire.

I ran out of time - my flight to the location of the AGC is tomorrow morning. I had envisioned a full set of tests with the Arduino Uno test driver setup, but I will have to do that from my hotel room, in my spare time.

I carefully moved the unit and all its attached boards over to my carry-on, placing T-shirts between layers since I expect this may get a close inspection by TSA tomorrow.

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