Celation's Hartnell/Troughton Console Build

[celation]

Sorry - see what you mean. No - nothing in there at the moment.

I think 8 per box will probably be enough. When it's fresnelled (is that a verb?) through the lens, it should be fine. We'll see.

Yes - the fading thing. I reckon I might be able to achieve this by putting a capacitor in combination with the LED. Might look into that.

[Rassilons Rod]

Ooh! Capacitor! Good call

I'm no expert on electronics, but I do know that when you power down a laptop and the LED on the PSU stays on, that's why.

Sounds like you're on to a winner

[kert gantry]

The 3rd Doctor was stranded with his TARDIS disabled, and in all of those episodes where he was rewiring this and that, it's easy to say that many of the console's controls had different functions when he was done with it (not to mention the "mangler" job the 4th Doctor did to the console in "The Horns of Nimon"!).

Sounds like the old story about the guy who gets a visit from a dud electrician.  Now every time he flicks a light switch all the taps turn on.

Glad you like my theory Dino.  Yeah, we knew as far back as Edge of Destruction that the ship had a degree of sentience, so I like to think of its telepathic capabilities as more of an all-over thing, rather than being confined to one little panel.

Agree with you too about the Hartnell console being the best 'classic' series version.  I just hope Celation's recreation, when finished, will get a much longer and more pampered life than its ancestor did!

[Rassilons Rod]

Yeah, we knew as far back as Edge of Destruction that the ship had a degree of sentience, so I like to think of its telepathic capabilities as more of an all-over thing, rather than being confined to one little panel.

I don't often do spoilers, but when I do....

Spoiler

"EXTRACTION FANS ON!"

[close]

[galacticprobe]

Yes - the fading thing. I reckon I might be able to achieve this by putting a capacitor in combination with the LED. Might look into that.

I have vague memories of seeing something like this on some of the equipment I used to work on, and the only function it seemed to serve was to have the Power LED "dim out" once the power was turned off. Unless I'm wrong the circuit was something like:

Pos (from chase_____________
  circuit output)          |         |
                            Cap      LED
                               |         |
                          Resistor  LED's resistor
                         (variable)   |
Neg (return side______|______|
  or ground/earth)

The cap will charge when the LED has power to it, and once the power is removed the cap with discharge through the LED, thereby causing it to "fade out" rather than just blink off. Depending on how you adjust the variable resistor under the cap determines the fade-out time of the LED. That should give you the "trailing" effect of an incandescent bulb.

It's far simpler than some of the other LED fading methods I've seen posted on the web, but hopefully this at least gives you something you can experiment with.

Dino.

[celation]

Ah - thank you Dino!

I had read that a capacitor should be placed in parallel, but it didn't seem right, somehow. Good to have it confirmed. I'll have a go at that at some point.

Cheers,

C.

[Rassilons Rod]

Well, here's how the demat lever box was constructed - fairly rough'n'ready:

Sorry to bring up an old topic. I just wanted to ask, how much of a border is around the curved part of the large lever.

The sides look narrower than the front and back, the sides I can figure out from the thickness of the curved part, but how much is
front and back and how much of the circle sticks above the top surface?

Cheers,
-Marc

[celation]

No problem. Off the top of my head, the borders at the sides are 0.5 inches. But you didn't want to know that one.

Not sure about the ends. Looks like an inch, but I can't remember at the moment. If I don't get back to you on that - remind me.

[celation]

Okay - overall length of the large lever box is 9 inches. 7.5 inches of this is the curve of the circular section - with 0.75 inches of surround at each end.

And don't forget the 3/8 inch bevel around the edge.

Can't guarantee that's right, of course - but hat's what I have.

[Rassilons Rod]

That's awesome, thanks

[Rassilons Rod]

Also...
Would you agree with this assessment of the panel numbers?

[celation]

Ooh - very nice!

That's the numbering system I'm using - yes.

[Rassilons Rod]

Thanks

[marinedalek]

On the subject of fading lights - if they're always going to be either off or running at a certain speed, you don't have to use capacitors. It's possible to "cascade" diodes and resistors in a loop, so that the LED you apply power to is brightest, while the two or three after it are progressively dimmer.

The capacitor circuit above has two potential pitfalls that I can see. First of all the capacitor is directly across the power rail for that LED. This means that when your chase controller (often a decade counter IC) output switches off, there's still a substantial voltage on the output pin courtesy of the capacitor. A notable thing about IC outputs is that they don't like having voltages applied to them - it tends to let the magic smoke out  . As for the resistor in series with it, all that would do is slow the charging of the capacitor. The LED already has a resistor in series with it, so it doesn't need a further reduction in current from the capacitor; indeed such a reduction would cause a noticeable blip of dimming rather than a smooth fade. The only way to really control the fade out rate is to change the size of the capacitor.

There are ways of simulating a light bulb-type fade with LEDs but the circuits can get quite complex quickly, especially if you have eight independent fade-out circuits for each chaser.
Here's a circuit that someone's designed which uses transistors to achieve this. If you replaced the switch with the output from the case circuit, followed by a diode then it would work, but as I say it would perhaps be overkill.

Another option is to just use bulbs and a suitable high power output chase circuit

[galacticprobe]

The circuit above wouldn't have any power sitting on the counter chip's output long enough for it to damage the chip once the counter "clicked" to the next stage in the count. (If you're using a 4017 Decade Counter, they're almost as bullet-proof as the NE555 Timer chip used to advance the counter.) And if this is a concern, simply placing a regular diode between the output leg of the counter and the cap, you will stop any "backwash" the cap may cause. (Sort of like this:)

Pos_____+Diode-________
                            |
                          Cap
(The + and - symbols denoting the polarity of the diode: when this output of the counter turns off, the - (cathode, or negative side of the diode) will prevent any reverse flow of the current caused by the + charge sitting on the cap. That charge will bleed off through the LED, which is what causes the fade-out.)

Yes, the resister under the cap would slow the charging time of the cap, but without it the cap would effectively look like a short circuit to the counter chip's output and this is what can cause chip damage. You need some sort of resistance there. Since that part of the circuit is in parallel with the LED both the cap and LED will get the same voltage applied to them. Yes, the current flowing through each leg (cap and LED) will be divided, but unless you have a very small resistor in series with the cap (which you shouldn't - it should be larger than that with the LED), the LED brightness shouldn't be noticeably affected. (Another reason why I said "experiment" with a variable resistor in line with the cap: to adjust the "fade" time of the LED, and this would also reveal if there would be any noticeable difference in the LED's brightness.)

As for the resistor under the LED, not all LEDs are build with resistors in them. If you use an LED that is just an LED, and not one with a built-in resistor, you will short out the counter's output because an LED is basically a one-way wire: current flows through it in one direction only, but it offers no resistance; current won't flow through it on the other direction (unless you have one of those bi-color/bi-directional LEDs, but that's a story for another day). The only way to get current to flow backwards through an LED (or regular diode for that matter) is to overload it, and that's not likely to happen with this type of circuit.

True, LED dimmer circuits can get complicated, but why go that route when a simple solution will work just as well, and cost less?

Dino.