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

[alreadyRogue]

i have heard that 6 V will fry the FX boards
which is why the voltage regulator will save it
but what the transistor does is act like a switch
when voltage is applied to the emitter pin (middle one) it closes the switch between the base (left) and collector (right) so all the juice from your battery pumps into the rotary switch and in turn into the LEDs

[Matt Thorn]

i have heard that 6 V will fry the FX boards which is why the voltage regulator will save it
but what the transistor does is act like a switch when voltage is applied to the emitter pin (middle one) it closes the switch between the base (left) and collector (right) so all the juice from your battery pumps into the rotary switch and in turn into the LEDs

I've used plenty of Force FX boards at 6V with no problems. In terms of getting the brightest, most predictable results, having buckpucks for all four chips would be ideal, but there's no way I could fit more than one buckpuck inside this hilt, and even one might be hard to squeeze in. If only buckpucks were smaller.

[alreadyRogue]

Here is what I would suggest
replace the alkalines with the NiMH from the shop, they will have a much better battery life as they will not loose their energy to heat through the resistors (due to the impossibility of buckpucks) because their voltage is closer to the voltage needed for the LED
because the dies are in parallel, they will draw much more current, and if at all possible i would HIGHLY suggest replacing the 4AAA pack with a 4AA pack, plus you can put the sound board over it and save space
the run time would be tremendously improved (2.6 TIMES AS MUCH)
I can modify my diagram to show you exactly how to wire in the recharge port if you want
I believe it is a necessity

[Matt Thorn]

Here is what I would suggest
replace the alkalines with the NiMH from the shop, they will have a much better battery life as they will not loose their energy to heat through the resistors (due to the impossibility of buckpucks) because their voltage is closer to the voltage needed for the LED
because the dies are in parallel, they will draw much more current, and if at all possible i would HIGHLY suggest replacing the 4AAA pack with a 4AA pack, plus you can put the sound board over it and save space
the run time would be tremendously improved (2.6 TIMES AS MUCH)
I can modify my diagram to show you exactly how to wire in the recharge port if you want
I believe it is a necessity

Rogue, thanks for the advice. I'll be sure to tell the guy I'm making for that Ni-MHs are preferable, but I can't control what he puts in it, so I'll choose resistors based on 4AAA=6V.

Unfortunately, the 4AAA arrangement can't be changed at this point. The guy does not want a recharge-port setup. (Using two 14500 Li-Ions and a recharge port would have made this project much, much easier. Oh, and I've wired plenty of recharge ports, but thanks for the offer or help anyway.)

Run-time is a low priority for this guy, since it's primarily for show, rather than dueling. Here's what it looked like in green, before I knew he wanted it to be color-changing.

[Matt Thorn]

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

Wait. Looking at your diagram again, I'm confused. You show a bundle of wires coming from the Yoda board, joined into a red wire. The bundle from the board would be negative. And since the crash sensor is on the positive line...not hooking up the positive line from the board would seem to not be an option. I'm hoping the sketch of the negative wires from the board is an error, and that I can leave the negatives from the board unused. Otherwise, I may be back to square one. (Note that I am not at home right now and can't test this directly.)

EDIT: Double wait. This description...

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.

...contradicts your diagram.

[Matt Thorn]

Sorry to double-post, but this is not an addition to my previous post, but rather A Whole New Thing™.

I actually brushed away the cobwebs, turned my brain on (chug chug chug), did some studying, and may actually have comprehended exactly how the whole using-a-transistor-as-a-switch thing works, and how to make it work here.

I have yet to test it, but theoretically, this diagram should work. Note that the transistor is an NPN, not a PNP. I now understand why it has to be an NPN, but don't ask me to explain it. (Yeah, I have read numerous explanations of how it works, but since my brain was turned off and gathering cobwebs, I couldn't wrap my head around it till today.)

I left out the latching switch, clash sensor, and speaker, because they are hooked up in The Standard Fashion™.

EDIT: I added a 7805 5-Volt regulator, because the TIP120 NPN transistor can only handle 5V. (Still untested, though.)
EDIT 2: I simply could not get this to work. It looks good on paper, but either I'm messing something up, or something in the Force FX board renders this set-up unworkable. (Possibly the clash sensor on the positive lead?)



Now, I'm hoping some electronics-savvy member will check this for me, but in the meantime, I'll actually put it to the test. (Right after dinner.)

[Rhyen Skytracker]

Also keep in mind if the rotary switch is NOT a BCD then you would need to use a bunch of resistors to get the exact colors you want plus you would need to use diodes to keep the mixed colors from backfeeding when in different switch positions.

[Matt Thorn]

Also keep in mind if the rotary switch is NOT a BCD then you would need to use a bunch of resistors to get the exact colors you want plus you would need to use diodes to keep the mixed colors from backfeeding when in different switch positions.

It is in fact BCD. But I had to look up the meaning of "BCD" and check the datasheet to confirm. Thanks, Rhyen. So that tiny little switch has something like Zener diodes built in to prevent that sort of thing?

[Matt Thorn]

O-o-o-kay.

So much for theory and my capacity for comprehension thereof. Within seconds of connecting the ground line to the emitter and the positive from the Yoda board to the base, my TIP120 NPN transistor was giving off wisps of smoke. Which is particularly puzzling considering that the board wasn't even turned on, so the circuit should not have been complete. At least the board seems to be all right.



I am flummoxed, and back to square one. *sigh*

EDIT: Oh. Maybe it had something to do with giving 6V to a transistor rated for 5V.

[Skottsaber]

EDIT: Oh. Maybe it had something to do with giving 6V to a transistor rated for 5V.

Oops!
Was it a mistake on your part, or will you need a different transistor?