Lighting noob - questions regarding circuit analysis & L

[BuildinStuff]

Hey guys, I started a thread in General Modeling and was told to check this forum out.

I've started reading over the LEDs threads. I'm getting a general feel for how you guys are talking about using the LEDs. I'm still curious, though...

--Before you guys put together a circuit, do you do a circuit analysis (voltage & current in and out, etc.) or do you just "go to town?" I don't have a problem with analyzing the circuit, it's just a lot of running the math on each element of the circuit. Boy, that sound like a retarded excuse now that I've written it.

It seems to me - at least from the way the stickies read - that a lot of this is just "make sure you've got the right size resistor matched up to the right sized LED and then power it up with between 6 to 9 volts." Am I wrong?

--Are there LED sets out there that have an integrated blinker in them already, or do you guys think its more reliable to just hunker down and build the blinking circuit using a chip? I wired up a REAL basic circuit a few days ago with a 555 chip - I used the "make a blinking light" tutorial in one of the circuitry books I picked up - and I'm wondering if there's a way I can eliminate the multitude of wires going in and out of that circuit.

[tetsujin]

Hey guys, I started a thread in General Modeling and was told to check this forum out.

I've started reading over the LEDs threads. I'm getting a general feel for how you guys are talking about using the LEDs. I'm still curious, though...

--Before you guys put together a circuit, do you do a circuit analysis (voltage & current in and out, etc.) or do you just "go to town?" I don't have a problem with analyzing the circuit, it's just a lot of running the math on each element of the circuit. Boy, that sound like a retarded excuse now that I've written it.

My general approach is to consider the input voltage (from the battery or wall wart) to be within a certain range and a certain (estimated) potential current flow. That makes LED circuits pretty simple - you have your input voltage and you can assume it doesn't vary too much, and you just have to make sure the total of all your LEDs doesn't exceed the current limit of the source. In reality, it's not quite so simple - for instance, a significant increase in the current draw can cause the source voltage to decrease - so this approach is all about making sure your "comfortable margin" is comfortable enough.

As an example - let's say my power source is "somewhere between 4 and 6 volts". Eventually, of course, a battery will discharge down below that lower bound, and the circuit may fail at that point... But I design each individual LED circuit along those lines - a resistor large enough that the LED won't burn out at 6V, but small enough that it'll still operate at 4V... Then I wire up all the individual LED circuits in parallel, and I can pretty much treat them as separate entities. The only way I need to consider them as being all part of the same circuit is that I need to make sure they're not drawing too much power all at once... But I don't think of these individual series circuits as things that affect each other...

It seems to me - at least from the way the stickies read - that a lot of this is just "make sure you've got the right size resistor matched up to the right sized LED and then power it up with between 6 to 9 volts." Am I wrong?

It can get more sophisticated than that - for instance, the use of a constant-current source rather than a constant-voltage source (which reduces the need for resistors and can reduce the amount of wasted power - but can also complicate the inclusion of other circuitry like logic ICs.), or when there's a whole lot of LEDs in a single model you may need to be careful about how the circuit is designed, so that wasted power and dissipated heat is kept to a minimum.

--Are there LED sets out there that have an integrated blinker in them already, or do you guys think its more reliable to just hunker down and build the blinking circuit using a chip? I wired up a REAL basic circuit a few days ago with a 555 chip - I used the "make a blinking light" tutorial in one of the circuitry books I picked up - and I'm wondering if there's a way I can eliminate the multitude of wires going in and out of that circuit.

Yes, and yes. I wouldn't buy a self-blinking LED for a model generally because it's not uncommon that I'll need blinking to be synchronized (for instance, nav lights) or that I'll want fairly precise control over the blink rate or pattern. IMO there's not a terribly strong case these days for using discrete components or single-purpose ICs for controlling blinking these days - PICs are cheap, they operate with a minimum of external components, you get all the control you want over the blinking (even to the point of doing PWM if you like), and they can control a whole bunch of LEDs at once.

[jwrjr]

A thorough circuit analysis is not usually necessary for a model effects controller. It just isn't that complicated.
The 8-pin pic controllers are very good for this. Not that there is anything wrong with a 555 (once you really learn how to use it) but the 8-pin pics are not only much more versatile and controllable, but they can actually cost less than a 555 with the resistors and capacitors.

[Sparky]

The best place to start is general project architecture. If molding an existing object (ship/figure/scene) look at all the FXs you see or hear in any reference material you can find. Write them down: best guess timing, etc.

Then decide what you want to implement. Then design or hunt for solutions to each FX.

Decide how you want your model to be powered and controlled. Push button to activate an FX or running on a loop.

Basic planning for wiring and circuits can't be done until you've thought of what you want and where it will go. How many of us have wanted to add a fan or ceiling light, but it's a lot more work once the walls are up and sheet rocked. When building model its no fun to try to shoe-horn in some wires and LEDs after gluing down to many parts.

[jwrjr]

No doubt about two things - ALWAYS do your research. And the more thoroughly you have planned your project beforehand, the better. You can't avoid improvising some. It is better to keep that to a minimum.