How Not to Build a Clock With Retro Displays

Having been interested in electronics for 40 years or so, I thought I must have some vintage parts lying around with which I could enter the RETRO TECH CHALLENGE and sure enough I found 8 vintage displays from around 1975.

What could be difficult about turning these into an Arduino controlled clock !

Eight 40 year old displays - I will explain

Arduino.or not - please read on.

Arduino clock module

A bunch of 390 ohm resistors

3d printer to make display holder - i do not need to explain this

Searching the Internet did not reveal any specific information for these PINLITES.

I did find a website for a very similar display made by Wamco with 7 segments and using a multimeter I managed to confirm the pinout was the same.

The specification for the Wamco displays suggested a supply of 5V at 15mA.

I tried the PINLITE display at 5V and they did not illuminate,

Using a 10K pot and a 12V supply I managed to illuminate a filament at 12V.

A 390 ohm resistor in series with each filament seemed to suffice.

In order to drive the display I used 7 opto isolators to switch each segment on an off as required.

I wrote a small program to test each filament and everything appeared to work correctly. on a single display.

To drive 4 or 5 displays the obvious choice would be to multiplex the displays but as soon as a second display was added the display stopped working,

I think the way the filaments are linked internaly they cannot be multiplexed in the usual manner, but I stand to be corrected on this.

Due to the time constraints with the end of the competitiion looming I do not have the time to order new components and to rebuild the circuit as required.

It should be easy to switch all 29 filaments individualy and to make a working clock from the vintage displays but not in time for this competition.

I will maybe complete the clock and rewrite the instructable and enter it into the next clock competition on Instructables.

I have included an image of the hard wired display setup because even a stopped clock is right twice a day.

This gives an idea of what I was aiming for.

My box of displays contained eight of these pinlite displays.

When testing with a multimeter I noticed one had the common seven segment pin mising.

And then there were seven.

I got the first segment to light up and selected the resistor value and it ran correctly, .but when the power supply was switched off and back on the filament burnt out and putting a meter across my PSU I noticed at switch on it peaked at nearly 20 Volts ( so much for careful component selection ).

And then there were six

All the remaining displays metered out correctly but 2 of the displays did not illuminate so again with a mult iturn pot I reduced the resistance until the display started to glow immeadiatly a filament burntout on each of these and I can only assume the inert gas in these had leaked over the years.

And then there were 4

I wanted to display the hours and minutes with a flashing indicator in between to show the clock was alive so I salvaged the one with the middle filament burnt out and intend to use the lower filament instead as can be seen in the first image.

Phew back to five !