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

[Matt Thorn]

I have been poring over my electronics books, the Internet, and scouring the forums, but I just can't get this to work.

Some of you may have been following this thread, where smarter folks than me figured out a great way to use a high-output PNP transistor to both 1) boost current to the main LED and 2) do the job that a relay would do.

Well, I've been trying to do the same thing with a Force FX board, but have had no luck.

One complicating factor is the clash sensor of the positive line coming from the Force FX board. (With the 2010 Electronic Lightsaber board, the positive line from the board is not used at all, and this poses no problem.) So I tried doing everything backwards, and using an NPN transistor instead of a PNP transistor.

If I've lost you already, either I'm not explaining well enough, or you don't have the electronic expertise necessary to help me out here.

I've heard plenty of people say that transistors are much more efficient than relays, yet I haven't heard of anyone using one with a Force FX board. Maybe that's because in most cases, the Force FX board provides enough current for the LED.

In my case, I'm using a LedEngin RGBA, with a 16-position rotary switch, so in some cases only one chip will be on, in other cases all four chips will be on. The board does provide enough current to light the LED, but it's not nearly as bright as it could be, and that's why I'd like to use a transistor.

I'm using a Yoda Force FX board and 4AAA alkaline battery pack.

Can any of our electronic wizzes out there toss off a diagram, or is this just not possible for some reason?

[FenderBender]

Alkaline AAA's put out less than 1A or 1A max. You can't pull more than that. Change to LI-Ion 18650s and see what happens

[Rhyen Skytracker]

Are you talking about the Yoda Force FX as in toy saber or the Yoda FX as in MR/Hasbro? Also, do you have pics of the board?

[Matt Thorn]

Thanks for the responses.

Fender, I think you may be mixing up mAh and mA. The AAAs have an mAh of 1000, but using the same 4AAA set-up and a BD242 PNP transistor, I was able to boost the paltry 21mA output from a 2010 Electronic Lightsaber board to 1180mA, and I recall Rhyen saying he was able to get much more current using a TIP42 transistor using AAAs.

I would prefer to use Li-Ions, but the guy I'm making it for wants alkalines, and it's all going into the teeny, tiny space of a Korbanth Luke ROTJ hilt. (Color-changing, no less, with a Hero-style control box with triangular LEDs that actually light up.) So 4AAAs is the best I can do. As you can see from the photo and video, I custom-made a battery-case/chassis (3D printed by Shapeways), so there's no turning back.

Rhyen, I mean "Force FX" as in the "high-end" saber boards, not the toys. (Although there's a "Force Action" toy, I'm pretty sure that "Force FX" is used only for the high-end MR/Hasbro sabers.)

[Rhyen Skytracker]

I was able to get around 1530mA using AA NiMH batteries not normal akaline batteries. I think with the AAA NiMH I was getting around 1300mA. You can get around 1200mA straight from the Yoda board by connecting all the 6 negative wire together. I would do that than to try to use a transistor. You can try the transistor by putting all 6 negative wires together and going to the base of the PNP transistor. I never use a transistor with the Yoda FX board because it puts out 1200 mA.

[FenderBender]

No, I wasn't mixing MA with MAH. AAA's don't put out much more (if at all) than 1A under load. AA's will put out more, and AAA NIMH's will, but not alkalines. You're just not going to get much more MA out of alkalines without a driver that converts extra vf to MA.

[Rhyen Skytracker]

Fender is correct. It was with the NiMH AA batteries that I got the high MA out of the transistor. How much mA are you needing?

[Matt Thorn]

No, I wasn't mixing MA with MAH. AAA's don't put out much more (if at all) than 1A under load. AA's will put out more, and AAA NIMH's will, but not alkalines. You're just not going to get much more MA out of alkalines without a driver that converts extra vf to MA.

I see. Sorry about that.

Fender is correct. It was with the NiMH AA batteries that I got the high MA out of the transistor. How much mA are you needing?

Now there's the $50,000 question. I'll be using an RGBA with a 16-position rotary switch, which means all 16 possible configurations of the four chips being on or off. And I'm not sure if the net effect of the rotary switch is to have the chips wired in series or in parallel. Better check into that.

I'm going to have to put on my thinking cap and calculate whether or not I can do a one-size-fits-all solution. But I'm still convinced there must be some way to use a transistor to get more current to the LED.

I also have to buy some fresh AAAs, because the ones I'm using are dying, and while I can get each of the chips to light up, the blue is barely there at all. (Green and blue have minimum forward voltage requirements of 3.2V, but at the moment the Yoda board is passing along just 2.8V.)

[Arkhan]

in the AAA form factor:

Energizer Advanced Lithiums are rated at 1000ma continuous, 1500 peak
Energizer Ultimate Lithiums are rated at 1500ma continuous, 2000 peak

http://www.energizer.com has tech .pdf that detail the discharge curves at various loads for all their batteries, lithium primary, nimh, alkaline, etc.

Obviously, neither of them is going to last very long at those kinds of loads, but they will output significantly more than alkaline, and provide 1.5V per battery, unlike the NIMH.


Order them in bulk. Don't buy them at Radio Shack ($4 a PIECE)

[Matt Thorn]

in the AAA form factor:

Energizer Advanced Lithiums are rated at 1000ma continuous, 1500 peak
Energizer Ultimate Lithiums are rated at 1500ma continuous, 2000 peak

http://www.energizer.com has tech .pdf that detail the discharge curves at various loads for all their batteries, lithium primary, nimh, alkaline, etc.

Obviously, neither of them is going to last very long at those kinds of loads, but they will output significantly more than alkaline, and provide 1.5V per battery, unlike the NIMH.


Order them in bulk. Don't buy them at Radio Shack ($4 a PIECE)

Lithium AAA batteries!? What rock have I been living under!? I had no idea such things even existed. And I just Googled and learned that I can buy them here in Japan (both Energizer and FujiFilm). But they sure aren't cheap, are they? Thanks for that info, Arkhan.

Anyway, I just put in fresh alkalines and got 5.8V from the Yoda board. But for some reason, when I try to measure the current, my Fluke 87 III gives me an "OL" error. My only concern is giving that much voltage to the red and amber chips, since the maximum forward voltages (according to the datasheet) are 2.6V and 2.7V respectively.

My brain hurts.