Trying to plan out electrical choices for future projects

[tetsujin]

I'm thinking of setting up various models of mine with a common interface: set them up to take the same voltage power supply and give them a data interface so I can control the lighting effects run by the microcontroller... There's various issues I'm trying to solve but one of the more frustrating ones at the moment is the question of what that common supply voltage should be.

A higher voltage (like 12V or 24V) would mean I could run more LEDs in series with less wasted power and fewer wires to and from the LEDs - but it would also mean that every single model with a microcontroller in it would need a voltage regulator, too, to drop voltage down to 5V.

A lower voltage (like 5V) would mean I could run microcontrollers without any additional power regulation circuitry, and so for simpler models without tons of LEDs going, the circuitry inside the models could be kept very simple. But then I wouldn't be able to run multiple white LEDs in series, for instance... Which in some cases would involve running additional wires to the LEDs, and in other cases might mean I'd need a DC-DC converter in order to get more voltage...

I'm not really sure which approach is better. I guess a lot depends on whether I expect most of my projects to require a LED driver or not... My most recent project doesn't have a ton of lights, but it has got eight white LEDs - in parallel, running at 10mA each, that's 80mA which is nearly at the limit of what my microcontroller can handle. I could get around that by adding driver transistors so that the microcontroller itself is no longer directly driving the LEDs - but I'm aiming to get most of the circuitry for the model collected in one place. It's less frustrating that way.

[macfrank]

I think lower voltages are usually better. Why not run a low voltage power bus (3.3V or 5V, GND) using either a heavier gauge bare wire (adequate for the current rating) or copper tape, the have the LEDs source or sink off the bus? I/O for the LEDs is cheap. You can always coat the bare wires/tape under a layer of primer or paint.

[Ziz]

Make a little male/female adapter cable with a resistor in it that you just install between the 12v supply and 5v model to reduce the current when necessary, remove it when it's not needed.

[tetsujin]

Make a little male/female adapter cable with a resistor in it that you just install between the 12v supply and 5v model to reduce the current when necessary, remove it when it's not needed.

A resistor won't regulate 12V down to 5V. If I hooked up a microcontroller that way I could fry it - or send it into brownout mode when the power requirements increased (i.e. when turning on lights)

At the very least it'd take a Zener diode to drop one known voltage down to another. To be safe, it'd take a regulator.

[Ziz]

Point is, do it as an adapter that can be moved from one model to another as needed rather than trying to force everything to be universal from beginning to end.

[tetsujin]

Point is, do it as an adapter that can be moved from one model to another as needed rather than trying to force everything to be universal from beginning to end.

I'm not sure that's right for what I'm trying to do. I want to be sure I don't hook up a model to the wrong power source by mistake, as that would be fatal to the microcontroller inside, and possibly some of the LEDs as well. (losing LEDs would be a lot worse than losing the micro...) I'm kind of being a bit secretive about what I need this for, I guess - but I'm going to be disconnecting and reconnecting these supplies a lot. If one screw-up kills the electronics in the model (or worse, the LEDs sealed up in remote parts of the model) then that's going to be hell in the likely event that I will, at some point, screw up.

I guess one solution would be to just start with 5V and then if I need a higher voltage for future stuff, make the connector mechanically incompatible with the one I use for 5V... Or if I had to go to a higher voltage later on I could probably retrofit the older stuff with voltage regulators...

[Ziz]

Point is, do it as an adapter that can be moved from one model to another as needed rather than trying to force everything to be universal from beginning to end.

I'm not sure that's right for what I'm trying to do. I want to be sure I don't hook up a model to the wrong power source by mistake, as that would be fatal to the microcontroller inside, and possibly some of the LEDs as well. (losing LEDs would be a lot worse than losing the micro...)

I guess one solution would be to just start with 5V and then if I need a higher voltage for future stuff, make the connector mechanically incompatible with the one I use for 5V... Or if I had to go to a higher voltage later on I could probably retrofit the older stuff with voltage regulators...

That was going to be my next suggestion - use connector style "A" on the 24v power adapter, the power input side of the module and models that use the adapters native voltage and connector style "B" on the model side of the circuit and models that use the modified voltage. That way you'll always know which models need which voltage because you won't be able to hook the power adapter up to a model that requires the module. In effect, the whole thing becomes a "square peg in a round hole" puzzle that would be impossible to screw up.

http://www.zizolfo.com/power-module.JPG

[Mr. Engineer]

This is a good topic. And since I am doing some circuits for the 1/350 Enterprise, I would be using a 12volt wall adaptor. At first, I was thinking of using a PC PSU but because its very bulky and noisy, I decided otherwise.

The reason is that for this project, each segment would have a microprocessor and so, each circuit would be using a voltage regulator to bring it down to 5 volts. Reason being is that I will use the 5 volts for the microprocessor and for most LEDs except for the Warp Nacelle where I would be using 12 volts.

Over here, 12 volt wall adaptors are very common. Moreover, if you need to show off your model from a car............ heh.