Yet another LED fade-in-out with a few caveats

Thread Starter

Moppusan

Joined Aug 24, 2017
5
Here in Pennsylvania the Renaissance Fair is going on through October and a friend invited my wife and I. I figured I'd make it fun and dress up as something...the only thing I'm certain on is a staff like I'm a mage, wizard, or what-have-you. I'd like to be able to illuminate my DIY "crystal" with a LED. I'm not *completely* new to electronics but things like what resister to use, what capacitor, how much voltage, etc. are mainly foreign to me.

Now, the caveats: I want to be able to hide this in my staff with a small button that would be covered by a small amount of wood or a wrap, whatever. I figured a 9v battery would be a good sized battery that would be easy to hide. And of course I would need it to snake up to the top where my "crystal" is. So far I think just one white 3mm 3v LED would be good.

I've seen the commonly-referenced video (I searched before posting) and it looks mostly like what I'd be doing. The "problem" of that design is perfectly fine for my project. I don't mind a delay before the LED starts fading in.
I figure about a 5 second fade-in time would work and a 3 second fade-out. Also, a "safety" switch would be great to have so I don't accidentally start illuminating my staff unless I want to.

I know it would (probably) be better for me to learn all of the ins and outs about circuits, resistors, capacitors, Ohm's law, etc., but this is just one project and I really don't see myself doing anything like this again. I humbly ask you, the experts, what parts I should get that would solve my dilemma and how to throw them together without soldering (I have plenty of electrical tape). The diameter of my wooden "dowel" is 1 1/4" and it's about 5 feet in length.

Thank you everyone for any help.
 
I have some mechanical ideas to start. A 9V battery is about 1" x 0.6 x 1.9". It won;t do well in a 1.5" diameter staff.

I'm assuming the switch in the same end as the hand?

Suppose, the following.

Somewhere "convienient", cut a rectangular hole that a battery would slip through. I'll define convienient later.

Drill a pilot hole with an extra long aircraft bit.
Hollow out the inside at the top with a Forestner bit to the top of the hole you dug for the battery.

Have it meet up with something like http://www.mouser.com/ProductDetail/Keystone-Electronics/968/
at the end of a long/thin PCB. with circular piece of say plastic at the ends, This basically helps you align the battery to a PCB with a circular end and some sort of grip. e.g an eye hook. Maybe a screw slot. Then something to use as a pull to get it out.

so a long PCB with round somethings on both ends that you can push, twist and pull out. Purpose is to be able to line up with a battery slid in the side and connect.

Actually, it probaby could go straight down and you can fit rounded pieces to fit into the sides and glued in place etc. Maybe cover it with tape or something.

At the top, which would be bored, put two slots into the side of the staff. Put a bar through it that has a tapped hole in the center. This provides a means to atttach the crystal. The LEDS may be able to be on the top and not embedded into the crystal.

Think of it as say 3 LEDS at the top with the top flanged to accept a "ball". The ball has a stud in it. This could be done with an EZ-Loc insert and some locktite.

Again, a little tape along the top to conceal the side holes.

Where does the button go: (thinking out loud)

Turn the xtal; push the xtal; a hidden side button.

Make things really magical and make it so you wear gloves with a magnet, so it only works for you. E.G. Hold staff in one place with a magnetic fingertip and push staff button.

I don't know what's feasable or easily doable. You will have to learn to solder.

It's an electro-mechanical problem.
 

Bernard

Joined Aug 7, 2008
5,784
Do you want the pulsation to be continuous when turned on or manually switched on for rise, manually switched off for fall as in posted example ?
A description of crystal please.
3 AA Alk. batteries will fit better & give longer life.
 

Thread Starter

Moppusan

Joined Aug 24, 2017
5
The "crystal" is just a lot of scotch tape clumped together to form basically a sphere with a hole at the bottom for mounting/LED fixture. I want the LED to stay on as long as I'm pressing the button then fade out when I release it. Also, with the "safety" switch that would keep the circuit open to prevent accidental illumination of the LED. Like a mini or micro SPST slide switch.

Maybe I should get a breadboard to test things.

Another question: would a whole circuit be OK to wrap in electrical tape? Being that I have limited space to begin with. I do have until some time in October to get this put together if I need to learn how to solder and need a pcb or whatever I'd have to do.
 

wayneh

Joined Sep 9, 2010
17,496
I want the LED to stay on as long as I'm pressing the button then fade out when I release it.
Is that all? If a fade-out is the only "effect" you need, that's a pretty simple thing to do.

Maybe I should get a breadboard to test things.
You can get by and do testing without a breadboard, but you absolutely should test at the lab bench (ie. kitchen table) before building anything. A breadboard makes this easier and is a great thing to have around if you think you might do future projects.

Another question: would a whole circuit be OK to wrap in electrical tape? Being that I have limited space to begin with. I do have until some time in October to get this put together if I need to learn how to solder and need a pcb or whatever I'd have to do.
I can't recommend electrical tape but this circuit will be simple enough to wire up without a board. To immobilize the parts and insulate any leads at risk of touching each other, I'd probably use hot glue. The biggest negative of that is that it's tough to clean off if you need to make changes.
 

Thread Starter

Moppusan

Joined Aug 24, 2017
5
Yeah, fade-in while a micro button is being pressed and fade-out when released is the only thing I want it to do. And that safety switch I've mentioned to keep the circuit open to avoid accidental light-ups. I just need to figure out what power source would be good enough and small enough to fit in a 1 1/4" dowel. The only real thing I need help with is what capacity capacitor and the resistors' ohm levels.

Is there an online calculator for things like that or do I need to read up on some basic electrical how-to?
 

Thread Starter

Moppusan

Joined Aug 24, 2017
5
Yes, fade-in when the button is pushed and stay on while the button is pushed, then fade-out when released. Something like 5 seconds fade in and about 2-3 seconds fade-out.
 

Thread Starter

Moppusan

Joined Aug 24, 2017
5
The diagram for the video I linked to in my first post is this. It's pretty much exactly what I want to do, but with only one LED and the safety switch added at the start. And probably not 12v, depending how I can wire a few batteries in series. I have 3 AAA batteries of questionable remaining charge...so that would be 4.5v. Not sure what voltage would be best for this application. I have a few Eneloop rechargeable AAs and I think 2 AAAs.

 

wayneh

Joined Sep 9, 2010
17,496
The diagram for the video I linked to in my first post is this. It's pretty much exactly what I want to do, but with only one LED and the safety switch added at the start. And probably not 12v, depending how I can wire a few batteries in series. I have 3 AAA batteries of questionable remaining charge...so that would be 4.5v. Not sure what voltage would be best for this application. I have a few Eneloop rechargeable AAs and I think 2 AAAs.
That's essentially the same as the simulation I've been working up, which is now working. (I had forgotten to include a ground. Forehead slap.) I haven't yet included the resistor to help drain the capacitor and that would help get isolated control of the fade up and fade down times.

Don't get confused by V2. That's just a technique for controlling the switch in the simulation. In real life there would just be a simple switch.

UPDATE - the attached simulation now includes that drain resistor R3. By playing with the values of R3 and C1, you can fine tune the fade-in and fade-out timing to your heart's content. You'll need LTspice to do that in simulation, but it may be better to actually build the circuit and just play with it. Your ideas may change once you see the actual results, the relative brightnesses and so on. You may decide that the shape of this ramp (an RC curve, steep initially and flattens) doesn't suit you. A linear ramp might look cooler, and can be achieved with a simple op-amp circuit. But one step at a time! BTW, I think a single 9V is a good choice for this project. You could consider using 2 LEDs in series to get more brightness.
 

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Bernard

Joined Aug 7, 2008
5,784
It might be helpful to try different LED's or combinations with just battery, 3 AA's, & resistor to find desired effect. I ground off the dome of a 30 mA white "piranha" , sanded & polished & came up with about 170 deg. spread and fairly bright @ 4.5V battery, 10 ohm & LED = 35 mA.
 
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