Using a transistor as a switch/amplifier with a Force FX board

[Novastar]

Yes, Matt you are correct... you do not want to feed ~5v or ~6v into LEDs (in this case, the LEDEngin reds/ambers) that are best with ~3 or ~3.5v max...

BTW... a quick lesson in batteries and how they are rated for "draw"... you'll usually see something like "2C" or "1.5C" or something if a spec sheet is offered.

What that means is "2 x the current/present capacity" and "1.5 x the present capacity"...

Therefore... if your cells are at max charge and have:
a 1500mAh rating... 2 x that (or 2C) would be 3A.
a 1500mAh rating... 1.5 x that (or 2C) would be 2250mA.

However... don't forget that the total capacity (quite naturally, duh!!) lowers as you use the batteries (again, DUH)... and therefore, you max draw will decrease as the cells get used up.

This is why you want a "C" rating (amp draw) that is fairly higher than the maximum you ever wish to draw. Since (hopefully) when your pack is even at 50% capacity... you may still be able to draw what is needed.

Almost lastly, I'll just say... when you have 4 dies (LEDEngins that "we" are using--we as in saber dudes)... you can wire:

* in series
* in parallel
* a mixture of these (what I like to call "paraseries" or "seriallel", lol)

FOR LEDS:

Wiring in series "keeps" the required amp draw, but DOUBLES voltage requirements...
Wiring in parallel "keeps" the voltage requirements but DOUBLES required amp draw...

For example...

LED = it wants ~3v @ 1A

Series of 2 of those LEDs = ~6v @ 1A needed/being drawn
Parallel of 2 of those LEDs = ~3v @ 2A needed/being drawn

Finally... now that I've said a THRONG... I'll close by saying that your choice of how you'll wire the dies will determine how much voltage and amp draw is going on. In some cases (of course) it's prohibitive...

Some boards can't handle ~7.4v... so you'd go in parallel...
Some boards can't handle ~4A... so you'd go in series...

And if you have problems feeding a device both ~7.4v ***AND*** are asking it to spit out ~4A--and it can't... uh oh!! Yer in trouble, and you probably need to do SOMEthing with "paraseries" or "seriallel"... lol. (if that even works)...

[alreadyRogue]

Matt if you are going to use the negative wire from the yoda you will still need an npn transistor. The difference between pnp and npn type transistors is the state of the base circuit. In a npn transistor the circuit is always closed (allows electricity to flow) unless voltage is applied to the emitter pin. In a pnp type transistor the circuit is normally open (no electricity) and when voltage is applied to the emitter pin the switch closes and the electrons flow.
Now if you want to use the negative wire from the MR board, all you will need to do is switch the polarity of the other wires. So if the emitter (from board) is negative, then both the base (from battery) and collector (to led) also need to be negative.
So your wiring should look something like this.
Battery plus terminal forks, goes to MR board and DIP switch, from MR board it goes to PNP type transistor ( reversed polarity as mentioned above), From dip switch it goes to the different dies of the LED. The negative wires from all the dies are combined, and that leads to the COLLECTOR pin of the transistor, thus completeing the loop.
Even though the transistor is on the negative side of the LED, the fact that it is still an open switch keeps electricity from flowing.
Hope that helps, if you want I will draw you up a complete circuit diagram.
EDIT: please note that NiMH bateries sold in the store can easily pit out 5, 6,or 7A easily where as the pcb for the Li-ions capps it at around 4.5A. I just want you to and your friend to be informed because you could be looking at 15-40 minute runtimes before you have to buy a new set if alkalines, which may not even drive the LEDs at their full capacity in the first place.

[Matt Thorn]

Nova, thanks for the info on batteries. I thought I had already learned everything there was to know on the topic from you, but it seems there always more to learn.

Rogue, sorry for the late response. It sounds like you're giving me exactly the info I'm looking for, but I haven't had a chance to wrap my head around it yet, and am working on a diagram at this very moment. I just want to clarify something. You wrote, "you will still need an npn transistor." Judging from what follows, I think you meant I still need a pnp transistor, correct?

[alreadyRogue]

Hey matt i just reread your post and found that you are using the positive wire right? but just to clear things up i decided to post a diagram of what i think you are trying to do

[Matt Thorn]

Hey matt i just reread your post and found that you are using the positive wire right? but just to clear things up i decided to post a diagram of what i think you are trying to do

That would be fantastic, Rogue, because I'm confused by this:

Now if you want to use the negative wire from the MR board, all you will need to do is switch the polarity of the other wires. So if the emitter (from board) is negative, then both the base (from battery) and collector (to led) also need to be negative.
So your wiring should look something like this.
Battery plus terminal forks, goes to MR board and DIP switch, from MR board it goes to PNP type transistor ( reversed polarity as mentioned above)

Positive or negative, whichever works is fine with me. I just know that when I tried to do something similar to what we did on the other thread, it didn't work.

[Rhyen Skytracker]

If you are using a BCD rotary switch it will work in parallel. When the switch goes to pos 4 and above it will just combine the two wires internally and that is like wiring them in parallel.

[alreadyRogue]

That should work
I forgot to upload the picture to my other post... sorry

[Matt Thorn]

If you are using a BCD rotary switch it will work in parallel. When the switch goes to pos 4 and above it will just combine the two wires internally and that is like wiring them in parallel.

I thought that was probably the case. Thanks for the confirmation!

That should work
I forgot to upload the picture to my other post... sorry

Brilliant! Can't wait to get home and try it. If it works, I should be able to finally finish this saber this weekend.

[alreadyRogue]

haha thanks
BUT
dont forget to put resistors/buckpucks/drivers between the bcd rotary and the led

[Matt Thorn]

haha thanks
BUT
dont forget to put resistors/buckpucks/drivers between the bcd rotary and the led

Okay. I was wondering if the 4.5V regulator was intended as a substitute for resistors on the red and amber LEDs. So, why did you include a regulator?