Finished testing DSKY project

FINAL CHECK FOR HIGH VOLTAGE AC LEAKS TO LOW VOLTAGE LINES

I did continuity tests and resistance tests for safety. All the relay coil wiring is low voltage DC (14V) while the contacts controlling the electroluminescent display are switching 275VAC 800 Hz. If the two mix, it won't be a good thing for the relay coils, diodes, nor for my driver transistor circuits and the Arduino. 

WIRING HIGH VOLTAGE 800HZ AC BETWEEN ALL MODULES

The high voltage is output from two sets of pins on the Power Supply Module, labeled 800LO and 800HI although the notion of low and high have no real meaning for alternating current. The 800LO side are connected to a pair of pins on the EL Display Panel Module that are called 'ground' but are really a common side of the many capacitors formed by the segments on the panel. 800LO is also connected to the Relay Module as it grounds segments when they don't have 800HI applied to them. 

The 800HI lines are tied directly to the pin on the EL Display Panel Module that illuminates lines and rectangles behind lettering, as well as to many input pins on the Relay Module. I suspect that having a separate 800HI for each column of the five bit relays for a digit helps with ground testing and checkout. It certainly isn't a matter of dividing up total current, because the usage of the entire display panel is quite slight. 

I took the time to clean up the small breadboard where I had built the replica of the output driver circuit inside the Apollo Guidance Computer which feeds an 800 Hz square wave into the first transformer of the Power Supply Module. On the Apollo spacecraft there is a dimmer (potentiometer) that can short part of the signal across the first transformer primary, thus reducing the output voltage and as a result, dimming the panel. I put in a 10K resistor which represents the dimmer wide open on the bright side. 

FIRST FULL POWER APPLICATION

With all digits and signs off, when I applied power I saw the lines and text blocks illuminated, showing that all appeared well. I had written a simple command language for the Arduino with verbs PROG, VERB, NOUN and SIGN for the display elements I am lighting. 

Firing up a serial monitor (terminal program) to the Arduino, I commanded that all digits be set to 8 and the sign be turned to plus. This lights all segments I have wired, confirming that the Power Supply Module is able to deliver consistent brightness even with all segments on. 

With all segments active I found that I have one segment that is not lighting. The rightmost digit of the VERB section is missing its top horizontal line. It turns a 6 into a b with that segment missing, but doesn't impact digits like 1 and 4 that don't use it. Tomorrow I will check through the wiring and do more testing until I know why this is happening and what actions will restore full operation.

I then issued a mix of commands causing different digits and signs to show on the EL Display Panel Module. Once the missing segment is working, this completes the entire project to demonstrate the use of Apollo hardware producing the display output. 

As a proof of concept, I set up the display with certain digits and a sign showing, then powered everything off. When I later switched on power, the same display is visible. This is due to the use of latching relays in the Relay Module. They retain their state even across a power outage and only consume current when switching on or off.