Help re-creating a replica movie prop

[skarkowtsky]

Hi all,

I'm an amateur replica movie prop maker, though completely unskilled with circuits. I'd like to re-create a briefcase that contains a thumb wheel switch and 12 4-digit LED readouts. I've identified the actual thumbwheel, a Digitran 23000.

The case should work as follows. Each 4-digit LED has its own toggle switch. In one position, the readout is off, in another it is on, revealing a 4-digit number. Whether it actually, functions or not, the end result is that the character in the movie dials in a number on the thumbwheel, flips a switch to one of the 4-digit LEDs, and the number is revealed, he then dials in another number, flips another switch, and that number is revealed on a different LED. He does this "12" times over two scenes in the movie.

I can't say that the prop functions for sure, but we do see him dial in 2 different numbers that reveal themselves on two separate readouts. They could have been pre-programmed, and he just spun a disconnected thumbwheel, or it could have actually functioned. It's all housed in transparent plexiglass, and I can see a lot of components and wires underneath. Again, these could all be dummies, or not.

The actual prop is owned by a fan, and although he won't reveal much of anything about it, he did state that the switches and readouts do function. He wouldn't say whether or not the 4-digit numbers were burned in to each readout, or if the thumbwheel controlled them. He also stated that the entire case is powered by (2) 9 volt batteries.

I do think it actually functions because there is what appears to be a glitch in the readouts when we first see the case. At first, the character is just getting started and only one of the 12 LED readouts is lit. It shows the number 1260. On the thumbwheel is 1160, and the character then flips a second switch that shows 1160 on a second LED readout. At the same time, the LED with 1260 changes to 1160, too. This seems like a bad wiring job, but it also seems like the wheel is actually driving the LEDs. If all the LEDs were pre-programmed, the first wouldn't have changed to the new number, right?

The movie was released in 1988, so please think about technology from that era when considering how to make this.

A huge thanks in advance!
John

 

[betwixt]

I worked on the design of a similar prop, for 'Skyfall' which not only worked but had a functional USB interface!
Can you show an image of a clip from the movie so we can see it. The design sounds trivial electronically but with 1988 technology might be a nightmare to wire up with that many displays.

Brian.

 

[skarkowtsky]

Wow, that's awesome! You seem like the man for the job. Here are two gifs I made of the film with my phone.

https://media.giphy.com/media/1xV6AizvCO9CyERBBD/giphy.gif

https://media.giphy.com/media/dYKJwVtg1djQ3tGot6/giphy.gif

Note on the second link how the 1260 (accidentally) changes to 1160, and 1160 is on the thumbwheel.

 

[BradtheRad]

Most of the readouts have unchanging numbers. It is easy to provide 10-15 mA of current to each desired LED in the display and produce any character you want. No counter or decoder IC required.

It looks as though 2 or 3 digits are changing. 2 or 3 IC's are sufficient to create a counting circuit. Add a switch to enable/disable count. Then another switch sends the identical value over to the second LED display.

 

[skarkowtsky]

Hi Brad,

Thanks for chiming in. I'm following you, sort of, but keep it even simpler, I'm a complete novice, haha. So, you think that most of the 4-digit LEDs have pre-programmed numbers, and maybe only a few of them are getting a signal from the thumbwheel??

I'm not sure what you mean by only 2-3 digits are getting a signal. Why wouldn't all 4 get them? Just curious.

 

[betwixt]

I think a "back to basics" electronics lesson is called for to avoid confusion.

Each digit is a package containing seven segments and a decimal dot. The segments are made from one or more LEDs in a translucent resin and have an opaque filling around them so that light can't stray from one illuminated segment to another. Normally, all the ends of the LEDs in each segment are joined so at the pins you have one common connection and one connection for each segment. WARNING: there are two variants on this and they are not interchangeable, one is called "common cathode" where each segments LED cathodes are linked together, the other is called "common anode" where the anode are joined together. The polarity to drive them is reversed from one to the other but externally and functionally they appear the same.

The different digits are made by passing current through different combinations of segments at the same time. We normally call them A, B, C, D, E, F, G and DP (for Decimal Point). 'A' is the top horizontal segment then they work clockwise to 'F' and 'G' is across the center. To make the segments light up a current has to be passed through them, note it is a current and not a voltage that is needed. If you apply a voltage directly across any segment it will almost certainly burn out immediately. The current can be set by adding a resistor in series with each segment, it mans you need a lot of resistors (12 displays * 4 digits * 8 segments = 384) if you want to be able to produce all combinations of digits on all displays. The resistor values are calculated like this:
(Supply voltage - LED Vf) / LED current in Amps.
The result will be in Ohms, you can find LED Vf from the manufacturers data sheet but for a typical red 1 inch (25mm) display it won't be far from 2.0V and you should aim for a current of about 10mA (0.01A). For example, if it was to run from 12V, the resistors should be (12 - 2)/0.01 = 1K Ohms.

For your simple prop, all you need to do is direct the current through the switches to the segments (via the resistors) to make the digit shapes you want.

This isn't the way it is normally done in electronic counters but I'm guessing you don't want to get involved in multiplexing circuits and complex software.

Brian.

 

[BradtheRad]

Your videos show one readout being changed, then that number is copied to another readout.
It's ambitious enough at this time for you to try building a circuit which does the job for two readouts only.

I see the thumbwheel has 4 digits. So the thumbwheel really does send those 4 digits to one readout. Then he flips 1 of 12 toggle switches next to another readout, copying the number to that readout.

The readouts have 4 numerals. Each numeral uses 4 bits, so it sends 4 wires. Presumably this makes 16 data wires coming from the thumbwheel (in addition to power supply wires).

Each numeral needs to be decoded by a 4543 IC (or else 4511). This makes four ICs to drive 4 numerals. (There is a technique called multiplexing which reduces parts count, but it takes more knowledge and effort.)

All this was available since the 1970's.

- - - Updated - - -

Now I see Brian's expert post, telling how to light multiple 7-segment displays. As he says you're in for a nightmare of wiring, if you really wish to have full functionality for all 12 readouts.

 

[skarkowtsky]

Brian,

Thank you for that incredibly helpful introduction in to how the 7 segment LEDs function.

Brad,

Thank you for shedding light on what is and isn't possible. Also, I think the 4-digit number that appears on one display, but jumps to a second was a glitch. If you look at the second link, which occurs a few minutes later in the film, the number on the very first readout (bottom right) is completely different from the 1160.

Both,

So, is it possible, using techniques of that era, to make all 12 readouts display different 4-digit numbers assigned by the thumbwheel?

Also, there is a small red push button on the extreme left inside the case. Could that be a memory dump that wipes all 12 displays clean, to start over??

- - - Updated - - -

Each numeral needs to be decoded by a 4543 IC (or else 4511). This makes four ICs to drive 4 numerals.

So, I might be able to shed light on this!

Not possible to see in the compressed gifs, but in the Blu Ray, it's clearly visible that beneath each of the 12 readouts are groups of at least 4 long black components with 16 silver pins (8 on each side).

Could these be the above quoted components??

 

[schmitt trigger]

My two yen advice;
7-segment LED displays are relatively straightforward to drive. Having said this.....
Whatever circuit you end up with, the amount of individual wires can be staggering, even with multiplexing.

To avoid this, you really have to layout a PC board. You can replicate the exact same board for all 12 displays.

With respect to the 80s retro look, thru hole components are still available. As long as your board uses them, it will be indistinguishable from one manufactured back in the time.

 

[betwixt]

Could these be the above quoted components??

Well, if I had to design a functional (as opposed to 'for display purposes only') I would use dedicated multiplexer devices such as the MAX7219 or MAX7221 which would drive 8 digits each so six would be needed for 12 x 4 digit displays and they could be driven by a single small microcontroller. I think I could do the whole thing in 8 ICs. The wiring is FAR simpler and fewer components are needed but you do have to write some software and if it was used as a real movie prop you would have to be careful of strobe effects between the multiplexing and camera shutter speed.

Explanation: multiplexing is the process of cheating your eyes into thinking a digit is steady when it is in fact flashing on and off very rapidly. Eyes have 'persistence of vision' meaning they are insensitive to rapid flickering. With a multiplexed display, only one digit in each group is actually lit up at a time and the active one quickly moves from one display to the next. When done fast enough it looks like all the digits are on at the same time. The advantage electronically is far fewer connections are needed, for example, using a MAX7219 you need one wire to each digit's common pin and one wire to all the same segment paralleled across the displays. For an 8 digit display (or 2 x 4 digits) you then need eight wires, one for each digit and eight wires, one for each segment giving a total of 16 wires. In comparison, if you wire every segment individually you need eight common wires and eight segment wires per digit (8 + (8 x 8)) = 72 wires!

Brian.

 

[skarkowtsky]

Hi Bianca,

Thank you for that thought. Thankfully, I am familiar with Persistence of Vision as well as shutter speed. Given that this was 1988, and taking into account the 280 degree shutter angles on film cameras, especially Panavision and Arri, amd not bring r tirely sure that software was used on circuitry in the 1980s, I don't think the multiplexer was used on the prop.

Regardless, what I really need, whichever way we go, is for one of you guys to draw me the diagram flrbow to make two readouts work, I think I'd be able to replicate another 10 for a total of 12.

But, keep in mind, I need a drawing for a 10 year old kid of "use this component and connect it to this wire, etc. I'm handy with a soldering iron, but I cannot reads schematic. I need almost a cartoon illustration and literally representation.

Are you interested in helpinge achieve this? I can compensate you within reason for your time.

- - - Updated - - -

Sorry about the typos, Brian. Phone autocorrect.

 

[skarkowtsky]

I bought this for $16 from Amazon. I 'm opening it to see how it's wired, and maybe can replicate it for the prop. Of course, I would leave out the countdown feature. Is this a good place to start?



Thanks!
John

 

[d123]

Hi,

The following are not especially the exact path you are going down, but useful learning tools, in my opinion.

This is cobweb-free in order to see the general idea. The CA3161 and CA3162 make up an ADC and a SSD driver, once upon a time... but the schematic is reasonably simple to begin to comprehend what to be aiming for with your circuit (except the ADC, of course). Delighful CA3161/2 were my first ADC for a temperature sensor when I had zilch electronics experience and I got them to work, so presumably you'll also be able to get the gist and understand how these SSD drivers work, I hope. Harris Semiconductor, sweet words indeed.



From there, looking at old devices like the CD4026/CD4033 or the (HEF)4511, with inscrutible schematic "typical applications" are a further intro. to what previous posts by members are suggesting as the path to follow. Old ADCs like 7107 or 7135 may assist in the goal but you might find those a bit confusing, or they may help in a roundabout way.

This is a very nice, simple tutorial to understand the premise with basic drawings, as you requested: 7-segment-display-tutorial

I think it's hard to make a kiddie's drawing of this circuit without either creating wiring spaghetti that will be confusing or abstract diagrams with "lumped" wiring that will also end up a little confusing at first glance, perhaps, so an approach is to take the bull by the horns and learn to "know your enemy".

Good luck!

The term display decoder driver will help in this adventure.

 

[skarkowtsky]

Thanks for providing helpful examples, D123. I found the below YouTube video earlier and it seems like exactly what I need to do. I was even able to make sense of the schematic after watching the video a few times. All I have to do is swap the DIP switch for my thumbwheel. I’m currently looking at the Digitran 23000 datasheet to better understand the pin out.

With that being said, if I successfully make the circuit in the video with my thumb wheel, how do I add another 11 of them?
Do I literally solder all 12 of these onto the thumbwheel tabs??

Please check out the 45 second video:
https://youtu.be/ghlzoGkoijI

 

[betwixt]

Doing it that way means you have to replicate the circuit for every digit which makes it very complicated.

All this boils down to whether it has to be functional, in the sense that it works out what digits are to be shown by itself and maybe can change them by itself, or, whether it simply shows the numbers you dial in on the switches. Rather like lots of light bulbs and a switch to turn each one off or on.

If it only has to obey the switches, by far the simplest way to wire it is with a resistor to each segment and route the current through the switch contacts. Each switch position giving a different digit. The current combinations to make 0-9 and A,b,c,d,E,f can be made with nothing more than diodes.

You might find this interesting:
https://www.ebay.co.uk/sch/i.html?_....TRS0&_nkw=4+digit+7+segment+display&_sacat=0
but bear in mind that almost all commercial multi-digit displays use multiplexing as described earlier.

Brian.

 

[skarkowtsky]

But doesn't the number on the thumb wheel have to be decoded??

And to retain a number before moving on to another set of 4 Digit LEDs, I'll need the 4511 latch, right?

How do I wire all 12 4 Digit LEDs readouts into one thumbwheel switch?

I did the math, it's 260 wires!

 

[d123]

But doesn't the number on the thumb wheel have to be decoded??

I think not. It never changes from 1160. The switch turns on the display from what we see, the thumbwheel is aesthetic, not functional I think. The SSDs can be hardwired to display whatever you like. Even two is a lot of wires, as noted.

And to retain a number before moving on to another set of 4 Digit LEDs, I'll need the 4511 latch, right?

What do you mean? Not sure I'm keeping up. Each 4-digit SSD only shows one figure (ignoring the glitch), doesn't it?

How do I wire all 12 4 Digit LEDs readouts into one thumbwheel switch?

You would have to be insane to even contemplate doing that and go doubly insane trying to do so. . It's not necessary.

I did the math, it's 260 wires!

See posts 7, 9, and I'll guess a few of Brian's. Most of the weight in that briefcase must be the wiring.

Be prepared to make a few inevitable mistakes and have to re-do a wire or 10... Labelling with painter's tape may help a lot to reduce headaches along the way.

 

[skarkowtsky]

So, you guys are suggesting iassign static numbers to 11 of the 12, and just hook up the last one to the switch so that functions?

- - - Updated - - -

I think it functions because on the blu ray, you see (4 ) 4451-type components underneath each of the 12 readouts.

Unless the prop master was committed to authenticity, I don't see why he'd add all those components underneath a layer of red plexiglass that's already obscuring the guts.

 

[d123]

Hi,

I am, can't speak for other members.

RE the prop master: All roads lead to Rome, just some are more convoluted and take longer to get there. I have no idea how that prop was put together or why it is as you describe, but my few years of electronics have made me see that KISS is important, as is being as lazy and time-efficient as possible, if you understand the latter as facetious yet serious. I'm guessing the prop master looked at a few similar devices and could have even used a few dummy solder practice ICs to pad out the thing to make it realistic, for example, but who knows.

I personally would assign static numbers to as many as possible and only make functional what really, really needs to be so.

I'm thinking that multiple ICs or not, perhaps an avenue to pursue is looking into using a 4-digit SSD with all the pins on the SSD, i.e. and just e.g. Kingbright have these ones. One online retailer sells them at around $4 each, presumably 12 would work out a little cheaper. At least that way several/multiple 4511 type ICs can be omitted from the design, unless required for realism but would no longer needed to be functional. I'm thinking that this approach should cut down a lot on a headache of wires.

 

[skarkowtsky]

Clearly you all have experience. I have none, I make no mistake about that. And although I know you're all correct in saying wiring the entire box will be a nightmare, a really big part of me wants to make all 12 receive a working signal from the thumbwheel. I understand that I'm looking at well over 350 wires in total, but hey, I'll come out the other side with a wee bit more knowledge of circuitry.

I look at this exercise as tedious, arduos even, but fun and exciting.

Who's with me to make everything to function?