# Updating a 1980s circuit board design

#### metermannd

Joined Oct 25, 2020
83
So here's what I've sketched up as far as the Arduino setup goes.

Top part has the Arduino setup as I see it.
The bottom left I need to figure how much I still need in regards to buffering and pull-ups - this is where the address / data / control lines came into the add-on board.
The bottom right is that part that I've decided needs to stay (UUT interface).
The portion to the right of the line is the remnants of the glue logic broken down and ready to translate into Arduino code.

I've also worked out how the 4x20 LCD would be laid out:

Code:
--------------------
TEST: XX   LD A:____
XXXXXXXX   LD B:____
STAT:____  LD C:____
INSTALL    LD D:____
--------------------

TEST replaces the left 2 7-segment displays [4514: Q9, Q8]
XXXXXXXX is the keypad input line (7 digits + checksum) [4514: Q7-Q0]
STAT replaces the Go / No-Go LED pair [4514: Q15]
INSTALL only displays (flashes) when invoked / replaces the INSTALLING LED [4514: Q14]
LD A through LD D replace the corresponding LED pair [4514: Q10-Q13]

Cathodes driven by 7-segment driver and from B port / blanking line on 8279
Anodes driven by 4514 driven by SL port on 8279

Each instance of ____ is blank when the LED pair is off, PASS for green, NOGO for red
LED segment A drives anodes for PASS (green) LEDs
LED segment G drives anodes for NOGO LEDs and INSTALLING LED

Or is that too complex? Will post same over on the Arduino forum shortly.

#### Attachments

• 156.1 KB Views: 3

#### metermannd

Joined Oct 25, 2020
83
After further conversation with the folks at the Arduino board, I may have overestimated the feasibility and underestimated the complexity. Putting this on the back burner for the time being.

#### nsaspook

Joined Aug 27, 2009
7,869

#### metermannd

Joined Oct 25, 2020
83
Well, long story short, given that I was able to get a NOS 8279 controller IC, and after discussion on the Arduino forum as to whether what I wanted was even possible, for the moment, I am continuing with cleaning up the existing design to accommodate IC availability.

On that front, I've already made a few tweaks to the existing design by switching out the RAM (replacing the 6561s with a 6116), moving the 8279 from the display to the logic board, making a decision on the unit's testing range (eliminating one option that was very rare even when new, also simplifying the design a bit), and found drop-in substitutes for the old MAN74A displays and UDN2981A driver.

Now, I have a bit of a hiccup with the 7-segment circuitry. I found the MC14547 BCD/7-segment driver was obsolete, and have temporarily subbed in the trusty 74LS47 driver, but would like to know if there are other options (I checked into the Fairchild DM9368 but that's evidently obsolete too).

The last IC I'm having issues with is the MC14514 - this is still available but getting scarce. Do you think I should stick with it, or should I replace it with a pair of still common 74xx ICs - the 74LS154 4-16 decoder and 74LS375 latch?

#### Attachments

• 87.3 KB Views: 3
Last edited:

#### metermannd

Joined Oct 25, 2020
83
I have mostly finished working up a new design with replacements for a few obsolete parts, and removal of a couple sections that realistically have no chance of being used.

Looking at the feasibility of retooling the display to run on 5V only.

Also, I'm wondering about the best way to bring 5V / ground into this board.

On the original board, power and ground are brought in by way of a pair of DIP jumper cables (the cables that take place of the NVRAM ICs on the logic board)... is this an ideal approach, or should I be looking at bringing in a dedicated feed directly from the power board? Given that two DIP jumper cables were sufficient, would a 2-pin, .100" pitch connector be sufficient, or would I need to bump up to a .156" pitch connector?

If I opt for a dedicated power harness, would I be correct in assuming I would have to remove the power / ground connections from the incoming DIP sockets?