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Flashing Light Unit

Started by 12thdoctor, May 15, 2009, 09:49 pm

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kiwidoc

the asciimation circuit works a treat - he made one for me when he first developed the unit.

galacticprobe

May 15, 2011, 08:15 am #106 Last Edit: May 15, 2011, 08:16 am by galacticprobe
Ah, the old reliable 555 timer chip. Some things just never go out of style. As a former Coastie ET (Electronics Tech for those non military types) I worked with them quite often. I love those things! They can take a lot and keep going, but as shown in the diagram, if you're going to be using any bulb larger than a 12V car dashboard or standard side marker light, you'll need a power transistor to carry the current needed by the larger bulb, which is what that BUZ71 MOSFET does. And the nice thing about this circuit is that most of the components can be found in your local Radio Shack (although they may be less expensive in a general electronics supply store).

There used to be a small book called "The 555 Timer Cook Book" (or something like that) which had quite a few circuits in it like this one, so if you can find that somewhere it could give you even more options. (I think there's even a "555 Timer Experimenter's Handbook" out there. Pretty much the same thing as the "Cook Book", but the title might be easier to find.)

Dino.
"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"

slidin_sidewayz

Quote from: galacticprobe on May 15, 2011, 08:15 am
if you're going to be using any bulb larger than a 12V car dashboard or standard side marker light, you'll need a power transistor to carry the current needed by the larger bulb


Unless you use a relay. :-)

galacticprobe

May 15, 2011, 05:04 pm #108 Last Edit: May 15, 2011, 05:14 pm by galacticprobe
Quote from: slidin_sidewayz on May 15, 2011, 12:47 pm
Unless you use a relay. :-)


True: a relay would do the same as the transistor. The 555 would activate the relay (low current draw there) and the relay contacts would be the same as throwing a switch to turn the larger bulb on and off with the higher current going through the contacts: no extra load on the 555.

The only thing you risk going that route, depending on your relay and where you put it, is having a 'click' - 'click' - 'click'... every time the light turns on and off because relays are mechanical. Relay contacts also get dirty from carbon build-up; because they are a mechanical closure like a switch, there is a small amount of arcking when the contacts open and close, which leads to the build-up of carbon deposits, and just like the spark plugs in our car this carbon build-up will eventually block the current flow and the bulb won't light up. So, depending on how much you have your light flashing, the contacts will need cleaning at some point. This isn't a huge problem and most relay contacts can be cleaned quite well and easily with a rub of very fine sand paper (800 grit or higher) or a burnishing tool - we're talking a very fine abrasive here.

Transistors (like the BUZ71 MOSFET) are electronic and make no sound (that is, unless you get your ear dangerously close to them to hear a faint hum, but at that point your ear would actually be touching it and the hum you hear would be your own - yeah: think about that one :o). They also don't require cleaning unless you consider blowing dust off of the circuit every so often. Transistors may need an added heat sink (a metal "clip" with small wings or vanes on it which attaches to the transistor; in the diagram shown here it would attach to that little "plate" at the top where that little round hole is) if the light is going to be flashing for long periods. This is to help dissipate the heat caused by the current flowing through the transistor so the transistor doesn't burn out. But if the light is only going to flash briefly to go with sound effects every once in a while a heat sink shouldn't be needed. (That little plate with the hole in it is a small built-in heat sink for such things.)

Relays would be good for consoles, where clicks would add to the effect, but for the flashing light I'd stick with transistors like in the diagram. But, that's just my personal preference. And I hope my explanation above is useful to some members who weren't too familiar with the workings of electronics.

Dino.
"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"

slidin_sidewayz

Sir, you are indeed correct. A relay will most certainly click while operating. I doubt you'd ever need to clean the contacts in one, however. They do tend to work for many years in cars, no problem. I would use a transistorised system myself, and if a darlington was perhaps used in place of the main transistor in the diagram a larger wattage bulb could be used. I'm sure another, higher current transistor could be added on the output of the circuit as it stands to increase the load carrying ability instead. 555's are indeed cheap and reliable. I think this circuit will be a good one and could be played with successfully.

galacticprobe

May 17, 2011, 03:48 pm #110 Last Edit: May 17, 2011, 03:52 pm by galacticprobe
Maybe it's all the military electronics I've worked on over the decades, but it seemed like at least every six months or so someone (meaning equipment) needed its relay contacts cleaned. You are right in that they work for years in cars and such without needing to have their contacts cleaned. Maybe it has to do with how much power passes through the contacts? Higher wattage usually means more current flow, and that does tend to cause more arcking, and not that anyone would be using a 1,000 watt bulb in their lights, our ships' equipment often ran with that level of power, especially the transmiters which were full of relays.

We had one equipment cabinet - 19 inches wide, 24 inches deep, 7 feet tall - on one of my ships that was nothing but a bank of relays for reconfiguring the three computers that ran our Command and Control System. When we had to reconfigure things, we'd push a certain button and after all the relay-switching was "done", we'd have a bank of red LEDs that showed which relays hadn't closed (or opened as the case may be) because the arcking sort of "lightly spot welded" the contacts. And just like with the Doctor's TARDIS console, the procedure to correct this - and it was written in the manual for this cabinet - was to "lightly rap on the relay banks with a rubber mallet until the relays toggle." (More often than not that "lightly rap" turned into a repeated pounding until that last red LED finally went out!) This system was on ships built as late as 1990 and was finally upgraded in the late 1990s - less than ten years old, so I can see how a 900-year-old TARDIS would need a few pounds with a mallet every so often.

But anyway, back on track... As for power transistors (and I know they're old, but then so am I) I've always favored the 2N3055. Like the 555 timer, those power transistors can take quite a load (like a 55 watt halogen) and keep going like it was nothing. You wouldn't even need to heat sink them if the light was only flashing; their casing would easily dissipate enough of the heat.

Dino.
"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"

blackbird

This is my first post but I thought I'd throw this out there to see what you guys think.

I'm building a light weight, low-tech demountable 2005 Tardis to take to conventions and I wanted to have a light and sound effect for it.  I don't know much at all about electronics, but here's my plan.

I'll use a cheap old MP3 player with the Tardis sounds loaded on it, set to play on a loop of about 30 minutes.  It will have the landing / takeoff sound then 28 minutes of silence so it won't annoy people too much.

I'll run the MP3 player to this sound activated relay:
http://www.simplecircuitboards.com/Spec%20Sheets/Sound%20Activated%20Relay.pdf
This is intended to be used in haunted house setups to make lights flash or flicker with sound effects.  It has a sensitivity setting so it would flash with louder or higher pitched sounds.  Here is the "for sale" page for it:
http://www.simplecircuitboards.com/HauntedHouse.html

I'll then connect this to a 1,000 watt home theater surround sound system.

Theoretically the light will flicker on in sync with the volume of the landing and takeoff sounds.

The sound activated relay runs on 12 volts and I assume this 12 volts also powers the flashing light.  However I'm having trouble finding a light that will actually run on my 12v battery supply (a pack of 8 AA's). 
Does anyone know of any reliable light bulbs that actually work on a 12v pack made of AA's?  I have tried a few 12v light bulbs (including a car headlight) that don't seem to work.

slidin_sidewayz

Keep in mind that the lamp flashes at a particular rate completely irrespective of the sound.  In fact it flashes brightly even when the sound is low.  I looked at both ways with mine and decided the continuous flash rate was the only accurate way to mimic the real thing.  And it turned out great.  After all, it's not a Dalek.

wayne venomous

Here's something I've been working on:

Mark

Looks a very complicated set up, but it does give the desired effect.

I particularly like the fact it gives that fade when it goes out, as per the original TARDIS lamp.


wayne venomous

It's not as complicated as it looks, the main parts are the battery, charger, amplifier, mp3 player, sound-activated relay and the bulb itself.

The trick is the bulb is a low voltage 12 volt 60 watt rough-service bulb - because it's high wattage but low voltage it takes a while to illuminate and gradually fades up when switched on and fades down when power is cut from it. The battery acts as a "reservoir" as the surge from the bulb is ridiculous when it switches on and would overload the power supply from the charger.

slidin_sidewayz

And again, awesome bit of gear, Wayne. I just posted a question on your video page but I'll ask it here too: is that a Ring Modulator I see in the centre of that panel?

wayne venomous

Thanks!  :) Sorry, I didn't see the question  ???

It's a ring modulator but it's not connected up. It's actually a "test panel" I use for experimenting, the only part I was using in this video is the power amplifier, which is the board I keep adjusting the sound on.

galacticprobe

Apr 13, 2014, 06:32 am #118 Last Edit: Apr 13, 2014, 06:32 am by galacticprobe
Looks great, Wayne. That puts my buoy light flasher to shame. It can only handle a bulb roughly equivalent to a car's brake light. I might have to pull out my old electronics manuals (and experimenter's book) and start looking for a better circuit - one that can handle a larger watt bulb. Not to compete with you... just so mine doesn't look so pathetic. (I mean, it's great for a buoy at night on the ocean as it was intended, but for a TARDIS lamp? Erm... not so much these days.)

(Although I might still use my buoy light flasher for a 2005 TARDIS lamp, where the bulb is small enough to fit inside the little candle ring of the Gardman lantern. I can have the lamp and its base box sitting on a shelf, and just tell everyone that my TARDIS exploded, and this is all I've been able to find so far.)

And then call for a Scavenger hunt! ;D

Dino.
"What's wrong with being childish?! I like being childish." -3rd Doctor, "Terror of the Autons"

wayne venomous

It's just a 30 amp car relay that does the switching. There's no fading in the circuit as the effect is purely down to the light bulb I'm using!