Torpedo firing circuit

Falcon5768 · Post by **Falcon5768** » Mon Dec 29, 2008 2:58 pm

I love you! Im so going out and buying the Arduino starter kit to design my lighting for the Refit E

kitty · Post by **kitty** » Fri Jan 02, 2009 4:34 pm

Madman Lighting wrote:OK, I'm a little impressed but there's more to the story.

$15 gets you a bare expansion board with no parts and no microcontroller. If you want the small version that is the same size as my board and has a micro on it, thats $50 and you still dont get the LED drivers I have on mine and you have to write your own real-time code which is not trivial.

Arduino is an impressive set of micro boards and I may play with one someday. They're similar to the PIC BASIC stamp cards and some of the other micro controller proto boards out there and they do some pretty neat stuff, but not for $15.

-John C.

The i'duino (that's the one meant for a breadboard) costs 17.82 for a full kit including the PCB, microcontroller and all components and a presoldered FT232RL for the USB interface.
It is overkill for only a torpedo sequence, but i'm just saying.
You don't need LED drivers if torpedo sequence is all you want you can hook up 2 Leds with their individual resistors directly to the output pins.

You can even do it cheaper if you want.
You don't need to programm the microcontroller onboard, so you can omit the USB port completely so that takes care of the presoldered FT232RL and connector for the USB interface.
That leaves $5.18 for a bare board, add all the components except what's needed for the USB port and any ioport beyond 2 and you are way below $15.
You'd have to programm the microcontroller though, so that means you'd need 1 full i'duino to be able to programm those.
What's needed for a torpedo sequence alone however costs less than $15.00
And if you make a new design for only a torpedo sequence with only a cheaper and simpler microcontroller, the resistors, the 2 LEDS and a 16MHz resonator instead of a crystal oscilator, you should be able to do that for even less.
But at these prices i wouldn't even bother with that.

And if you are worried about the output not being able to drive a High Bright LED (but they will), you could add a BC547 darlington as driver for each led (those cost a few cents each)

I use the ULN2803A for driving LEDS, thats an array of 8 Darlingtons each capable of driving 500mA.
2 of those are sufficient to drive all the LEDS i want in a 1/350 PL Enterprise 1701-A.
And they cost less than €0.50 each.

Madman Lighting · Post by **Madman Lighting** » Mon Jan 05, 2009 12:38 pm

OK, I concede that you can build the micro for cheap.

May I humbly suggest you use a constant current source for your LEDs, esp your high current LEDs?

Sure, you can use a cheap darlington BJT to turn it on but what you may not know is that high current LEDs are very sensitive to changes in the driving current and can easily be over driven. You will also need a heat sink for those parts, they dissipate over a watt of heat each and without one, you're toast.

However, for small LEDs, a darlington array part will work fine as long as you provide a current limiting resistor.

-John C.

jwrjr · Post by **jwrjr** » Mon Jan 05, 2009 11:33 pm

That's why I like power mosfets. They don't draw current from the controlling device (not for our purposes, anyway. Technically they do, but it is miniscule) and, for practical purposes they are either full on or full off. This minimizes the heat that they give off.

Madman Lighting · Post by **Madman Lighting** » Tue Jan 06, 2009 9:22 pm

I use MOSFETs all day at work on switch mode power supplies.

I like LED drivers better for driving strings of LEDs. They provide constant current so you can drive any color you like with the same circuit. (Different colors have different voltage drops). What can happen with longer strings is the differences add up and one current limiting resistor wont cut it. If you drive with a constant current, that never happens.

kitty · Post by **kitty** » Wed Jan 07, 2009 1:55 pm

I don't use LEDs in serie anymore, so i give each led it's own resistor anyway, so the current usualy is stable enough, the highest current LEDs i ever used use for models are 30mA and i hardy use those at all.
My bright whites (10000 mcd or 12000 mcd, depending on the color) use 20mA typicaly at 3.8V and if i dare to look into one directly for a second i am blind for half an hour

That's enough light for my models and they cost me only €0.24 including metalfilm resistors.
For diffused red, green or yellow i go for my el cheapo 3mm, 80 degrees angle, 1.8 and 2.1 V LEDs which only cost 2 cents including the resistor.

I mainly use cheap cheap 8 pin microcontrollers with a ceramic resonator, because 6 I/O lines and a 4-6Mhz resonator is enough for most applications that don't have to be accurately timed.
I don't even program them myself, for a few pennies more they program them for me if i send the hex file.
I cannot be bothered with it for a few pennies.
using a resonator also lowers the component count and thus costs.

For my 1:350 PL enterprise 1701 refit however i want to have a few complex sequences and 14-16 different groups.

jwrjr · Post by **jwrjr** » Wed Jan 07, 2009 11:39 pm

That is another thing that I like about the 8-pin PICs - they come with an onboard clock oscillator. This is usually 8 mhz, calibrated to 1% with no external parts. You wouldn't build a clock with this, but it is plenty good enough for a model controller.