Help re-creating a replica movie prop

Naturally electronics is all that. Elements of science fiction. Elements of magic. It's one of those excellent things in life, to immerse yourself in a project for hours into the night. And to see success approaching as you work on it.

I agree it is sufficient for the time being if you set a simple goal, namely to modify your Amazon purchase so you add another readout, say. There will be revisions necessary just to do that much. After that you'll know better how to build the other 10 or 11 readouts.

I will help if possible but if you really want to jump in with both feet and make it fully functional, make life easy by buying four-digit multiplexed modules. They are not expensive and the groups of four digits are ready assembled with a mounting hole in each corner of the module, it is far simpler to build than having to mount 48 individual displays.

Multiplexing might cause flicker if you record the unit in action but as you seem experienced in videography, you can largely avoid it by using a low shutter speed so that several flashes per frame are captured and the light level is averaged rather than instantaneous.

You have a choice of 'bare' multiplexed displays or ones with a built in driver IC. There are several (incompatible!) types of driver IC but most seem to use one called TM1637 which is very clever and easy to use when only driving one group of digits but it has no way of being extended to more digits. It is really intended for things like front panel displays on home equipment rather than the much bigger application like yours. You can just duplicate it 12 times, it's a cheap option but wiring it to the switches is a bit more complicated.

You can also find four digit displays based on the MAX7219 from Maxim Semiconductors. These are much easier to extend to larger numbers of digits but as they are capable of diving 8 digits at once, most modules have all 8 digits on them and they are not easy to split into two groups of four. With the MAX7219 it is in theory possible to wire the whole 48 digits with only three wires!

Another possibility is to buy four digit 'LED only' modules and add your own MAX7219 IC to them. A little more wiring is involved but far less than a wire to each display. One MAX7219 can drive two four-digit modules so you only need six of them for the whole gadget.

The choice is yours, it can be done many ways. Something to consider - if you ever have all the digits showing '8', so all segments are lit at once, the combined current drawn will be around 384 * 0.01 Amps (number of segments times the current each uses), that is 3.8A which is quite a lot. If you use multiplexing it could be reduced to 6 * 8 * 0.01 Amps (digits in one multiplex * number of segments * current each uses) which makes 0.48A, about eight times less!

For information only - the 'bomb' in Skyfall used a single PIC18F4550 microcontroller that multiplexed 8 single digit LED modules. I had no say in the appearance and had to work to a layout and specification decided by the producer but I made a PCB and wrote software to drive it.

Brian.

I figured it out. I think I can make this. It's a wonky way with lots of wires, but everything will actually be driven off the Thumbwheel. I don't like the Multiplexing idea, sorry. I'm probably going to need help with the resistors and possibly wiring the toggle switch to both activate the latch and turn the 7-Segments on to show the number. I made these simple diagrams that I can follow.




Example showing Thumbwheel wired to Terminal Block that sends signal from each digit out to all LEDs simultaneously.

That is correct. The resistors you mention can be relatively high in value but you must have them. You show the thumbwheel switch as having four connections, there are actually five because one is common to the four others. Assuming you are going to use a normal binary or BCD thumbwheel, you have to connect the common to the positive supply (usually +5V) and each of the switched connections to the 4511 should also have a resistor to ground. The problem with driver ICs like the 4511 is if you leave an input pin disconnected (such as would happen if its switch contact was open) it can randomly be high or low and you see random flickering digits. The resistors to ground (we call them "pull-down" resistors) make sure the pin is at zero volts unless the switch closes and connects it to +5V, it is always in one or the other state.
I would suggest 47K resistors for the pull-downs.

You also need a pull down resistor on the LE pin. You show LT (lamp test) instead of LE (latch enable). LT and BI should always be connected to the positive supply for normal operation.

For the resistors in series with the LED segments I suggest 330 Ohms if you use a 5V supply and 680 Ohms if you use a 12V supply. The maximum voltage allowed is 15V.

Brian.

betwixt said:

That is correct.

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Brian, just to hear you say that I said or did something correctly gives me hope that I can do this.

betwixt said:

You show the thumbwheel switch as having four connections, there are actually five because one is common to the four others.

Click to expand...

My switch does have a 5th connection with a soldered rod running through all 4 switches. I guess that's what you're referring to?

betwixt said:

The problem with driver ICs like the 4511 is if you leave an input pin disconnected (such as would happen if its switch contact was open) it can randomly be high or low and you see random flickering digits. The resistors to ground (we call them "pull-down" resistors) make sure the pin is at zero volts unless the switch closes and connects it to +5V, it is always in one or the other state.
I would suggest 47K resistors for the pull-downs.

Click to expand...

With the 47K resistors, will I be able to use a toggle switch to turn the 7-Segments on and simultaneously activate the Latch Pin to show the number that was just dialed into the thumbwheel?

betwixt said:

I suggest 330 Ohms if you use a 5V supply and 680 Ohms if you use a 12V supply. The maximum voltage allowed is 15V.

Click to expand...

What about doing it the way the actual prop is wired: two 9 Volts presumably in parallel?

Thanks for all of your advice!

skarkowtsky said:

two 9 Volts presumably in parallel?

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It is common to use a 9V battery to power CMOS circuitry. I have a hunch the builder started with a single 9V, but found it died after a few minutes of shooting scenes.

So he put 2 in parallel. It's not an ideal arrangement. 9V batteries contain six little 1.5 V cells in series, smaller than AAA cells.
You might as well plan to have six AA in series. Current draw for your project (12 LED readouts, each 4 digits) can easily reach nearly 1 Ampere.
If you can manage to run your project at 6V, then four AA cells may be sufficient.
You should get several minutes of operation. It depends on whether you use alkalines (1.5V each) or rechargeables (1.2-1.3V each).

C cells are less common in the rechargeable type.
Rechargeable D cells often contain a AA cell in a D size shell.

Brian, just to hear you say that I said or did something correctly gives me hope that I can do this.

Click to expand...

Glad I made someones day!

My switch does have a 5th connection with a soldered rod running through all 4 switches. I guess that's what you're referring to?

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That type of switch is available in several variations. Some have 0-9 (decimal) and some have 0-15 (hexadecimal), the difference is in how many 'positions' or selections it is possible to make. In most electronic applications we use hexadecimal because it is more efficient but for the numbers 0-9 they are both the same. The reason is that each switch has one common side and four open/close sides, it is effectively four switches in one module that all operate together as the switch is turned. Don't confuse this with four digits, these are four BITs on one digit. The switches open and close in different combinations according to the number you selected and these can be read as a short through the contacts from the common to switched connections. Think of it is four toggle switches, all linked at one end but turning on an off in different combinations as each number is selected. In reality of course the toggle switches are part of one rotary mechanism. If you consider the open and closed combinations as '1' or '0' in binary, you can see that the selected position number produces the equivalent binary number on the switches. That's why the 4511 can decode the binary number back to a decimal digit. Going back to decimal and hexadecimal, you may have noticed that 0 to 9 doesn't use all the available combinations and there are in fact 16 different combinations of four bits:

0000 = 0
0001 = 1
0010 = 2
0011 = 3
0100 = 4
0101 = 5
0110 = 6
0111 = 7
1000 = 8
1001 = 9
1010 = A
1011 = B
1100 = C
1101 = D
1110 = E
1111 = F
The ones in bold are an extension of decimal to use the other combinations, we use the letters A-F in hexadecimal so they are not confused with other numbers, for example if instead of 'A' we used it's decimal equivalent of '10' it could me misinterpreted as a binary number. It's worth noting that the 4511 cannot decode the extra combinations and will probably result in a blank digit if one is selected.

With the 47K resistors, will I be able to use a toggle switch to turn the 7-Segments on and simultaneously activate the Latch Pin to show the number that was just dialed into the thumbwheel?

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Yes, the LE pin latches the number on the input pins. I laymans terms, it captures and snapshots and freezes the number so even if you change the input bits, the displayed digit stays the same. Operating the latch a second time will update with the number on the input pins at that time again. We use the LE normally so that counting processes are not seen 'live' on the digits and only the result is shown.

What about doing it the way the actual prop is wired: two 9 Volts presumably in parallel?

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I would be inclined to follow the advice already given. LEDs are fairly hungry in terms of the current they need so a substantial battery is advised. The voltage isn't critical but small batteries will drain very fast (a few minutes). If you can use a larger holder with several 'A' size batteries or bigger in series it will last much longer.

Brian.

Great news! I bought components to wire-up one digit to one 7-segment LED and it works. I am experiencing two issues, and need some help. I referenced the datasheet for the Texas Instruments CD4511BE chip and the Digitran 23000 thumbwheel to wire up properly.

Digitran labeled the switch outputs as A B C D on the sheet, but 2 1 4 8 on the actual tab on the switch. I had to experiment to get the configuration right on the breadboard, but I finally got it. A does not represent the first tab, which is a 2, it actually represents the second tab, which is a 1. B was actually the first tab, which was a 2, and so forth. Crazy!

My two issues:
1) On any digit, the segments that should be out are glowing around 30% illumination. The segments that should be on are full power and the number is visible.

2) When I first power up, 8 is displayed and I have to cycle through the entire thumbwheel once before the actual digit shows up on the 7-segment. I don't have the toggle wired to the Latch pin yet (can't figure it out). Could that be the reason?

Below is my actual circuit. The tan resistors in between the switch and the 4511 are 10k, and the blue between the 4511 and 7-segment are 1.3k. These are based off a website with a tutorial for doing this with a different type of switch. Maybe my resistors are too low? Yes, I used exposed resistors as jumpers from the 4511 to the 7-segment. I ran out of wire. Headed to the store now for supplies to wire that section properly.

You can see the 1, but also the remaining segments faintly glowing.


I'm so close on this. Once this functions, I can wire all 48. Any help to get this across the finish line is greatly appreciated!

Thanks,
John

Hi,

It looks like the breadboard power strip at the bottom needs + and -. you may have inadvertently crossed wiring somehow, therefore the dimly lit unused segments.

d123 said:

Hi,

It looks like the breadboard power strip at the bottom needs + and -. you may have inadvertently crossed wiring somehow, therefore the dimly lit unused segments.

Click to expand...

Thank you!

How do I fix??? Sorry, I stink at circuitry.

Are there two wires from the thumbwheel in pin 2 and none in pin 1 or is that just how it looks from the angle of the photo?

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Hi,

Don't be silly, it's confusing at first. Just put another + wire and a - wire from the top power strip to the lower strip as well, like "power jumpers".

It's a good idea to trim the resistors so they go in straight lines, and the wires too. It's easier to see what you're doing and troubleshoot issues. This is one example as a loose guide to the principle: **broken link removed**

And not likely your case, but beware bare wires touching other bare wires, such as resistor leads...

The edge blue and red stripes are to indicate negative and positive rails but they are not joined from side to side. You need to link the two blue ones and link the two red ones! Otherwise it looks OK. Yes, the latch needs to be fired to 'lock' the digit selected on the thumbwheel into the 4511 or it will show a random digit at start-up.

Brian.

Unfortunately, the power jumpers didn't work. Any other thoughts?

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betwixt said:

The edge blue and red stripes are to indicate negative and positive rails but they are not joined from side to side. You need to link the two blue ones and link the two red ones! Otherwise it looks OK. Yes, the latch needs to be fired to 'lock' the digit selected on the thumbwheel into the 4511 or it will show a random digit at start-up.

Brian.

Click to expand...

How do I link the two blues and two reds????

Hi,

I just told you. Put a wire from the red one to the other red one, and a black one from the blue strip to the other blue strip.

d123 said:

Hi,

I just told you. Put a wire from the red one to the other red one, and a black one from the blue strip to the other blue strip.

Click to expand...

I tried that, see above. it didn't change anything.

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GOT IT!!!

I re-read Brian's last post, and EVERYTHING on the bottom had to be ported over to the top. Looks great!!!

- - - Updated - - -

So, the big question. Can I use this exact wiring set up but purchase the 4-in-1 7 segment readout with all 4 digits in one unit??

skarkowtsky said:

GOT IT!!!
I re-read Brian's last post, and EVERYTHING on the bottom had to be ported over to the top. Looks great!!!

Click to expand...

Good news. You sped right along toward this milestone of success. It is common to try different logic polarity, in order to make the circuit work properly.

The multi-digit display is likely to be multiplexed. It won't have 28 pins (7 per digit). Instead it might have 4 pins for multiplexing, and 7 pins to serve all digits in a rotating manner. That makes 11 pins if we disregard decimal points.

Thanks, Brad. Ill continue on my original path of 48 single-digit displays. Buying everything right now.

If anyone is up for it, I still need help wiring the toggle switches. I’d like it turn the led on to display the number. I think it should simultaneously activate the 4511 latch so a specific 4-digit number displays on that readout. Is there a memory dump on a 4511 so I change a number already assigned to a display, or would the toggle in the OFF position reset it?

Also, there is a spring loaded momentary switch on the left side of the case. This button is clearly depressed when the case is closed, and extended when the case is open. There are two wires that run to it from the two 9 volts, so I'm guessing it’s the ON/OFF switch for everything and functions like a refrigerator light switch. I think I can wire this with an input from the batteries to a 12 pole terminal block going to each of the 12 circuits. Sound right?

skarkowtsky said:

I think it should simultaneously activate the 4511 latch so a specific 4-digit number displays on that readout. Is there a memory dump on a 4511 so I change a number already assigned to a display, or would the toggle in the OFF position reset it?

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You can load a desired number into the latch at powerup, by attaching resistors and diodes (to create binary) to pull input pins to either supply+ or 0V gnd.

You can pull an enable pin high or low briefly at powerup, by means of a capacitor-resistor network.

Also, there is a spring loaded momentary switch on the left side of the case. This button is clearly depressed when the case is closed, and extended when the case is open. There are two wires that run to it from the two 9 volts, so I'm guessing it’s the ON/OFF switch for everything and functions like a refrigerator light switch. I think I can wire this with an input from the batteries to a 12 pole terminal block going to each of the 12 circuits. Sound right?

Click to expand...

I'm beginning to suspect that only the led displays were turned off and on while shooting the scene. After turning on the latch IC's, they stayed on so that each IC retained its number.

It suggests that one 9V battery powers the latches continuously for several minutes (whether lid is up or down).
The other 9V powers the led's. They are lit only while the lid is open.

One binary switch can drive many 4511 devices, that is the strength of the CMOS technology they use. The current drawn into the input pins is so small that one control line can drive hundreds of devices (although there are other factors involved).

I'm beginning to suspect that only the led displays were turned off and on while shooting the scene. After turning on the latch IC's, they stayed on so that each IC retained its number.

Click to expand...

That's where you can use the 'BI' pin on the 4511 ICS. BI is "Blanking Input", normally used to turn the digit off completely when, for example, you don't want leading zero digits in a number. If you join all the BI pins together you can use them like a master on/off switch for the display but without turning the IC itself off. Add a pull-up resistor between the supply ando the BI pins and wire the case switch between BI and ground. Grounding BI makes the display turn off. If it works in reverse, wire the resistor to ground and the switch to supply instead.

What is the movie called? I may have it and can watch it for more tips.

Brian.

Major update!

I figured out that the common from the thumbwheel needs to be wired to the toggle switch, which is wired to the power supply. This allows me to dial any number on the thumbwheel, then turn the toggle on and reveal that number on the LED.

Brian, you were right, the BI pin gets wired directly into the output of the thumbwheel. This keeps the LED off until I flip the toggle to on to show the number.

The last thing (thankfully) I can't figure out is how to enable the latch, by which I mean, after I set a number on the thumbwheel, turn the toggle on, revela the number on the LED, I'm still able to change the number on the LED if I adjust the thumbwheel.

I need to freeze the number on the LED after I turn the toggle on. If I can get this last bit, I can wire up 12 readouts all with different numbers off the same thumbwheel.

Thanks again everyone!