Who said Hasbro FX must be boring? - LED string blade with FOC-like effect

[Obi1]

Hi,

Just these days I had some idle time and was wondering how to make those great looking Hasbro/MR lightsabers better. I simply love the sight of a LED string blade igniting, so I did not consider replacing the string with a single LED, also since I have such lightsabers with electronics from Plecter Labs. Inspired by the extra features of the High-end electronics, I wanted to devise a simple way of pimping an existing Hasbro FX with features I miss, foremost with a Flash when hit (only Erv can say if I'm allowed to use FoC here in this context...), because I felt that a static blade is simply too boring.

After spending some time to think about it and making a lot of measurements with a multimeter on an activated blade, I came up with a solution which actually requires only a single Transistor and the LED's you want to Flash when the blade is hit (in case someone already posted this idea, I did not find it, so sorry...)

It's just a teaser, in case someone is initerested, I can sketch the connection and the type of parts I used for the conversion.

On this Picture you can see the Transistor on a small PCB I directly attached to the LED sting PCB. In case you wonder how come the LED string looks strange, I managed to break the White PCB and had to rewire (price of excessibe modifications I guess, but it was worth this price).


This is the naked LED string of my HASBRO FX Darth Vader (removable blade).


In case of a hit, it lights up like this (here the normal LEDs are switched off for sake of better visibility). You can see that the Flash LED's are nearly doubling up the intensity.

...and one more thing: this same concept would work just as fine for a HP LED conversion in case you have a multi-dice LED!!!

Cheers: Andras (aka Obi1)

[Obi1]

Let's see how you can do this conversion.

First I needed to know how the Impact works in a Hasbro FX Lightsaber. After making some simple measurements with a multimeter, I came to the (right) conclusion, that the Impact Signal is connected to the Vdd pin (battery positive) via a weak pull-up (probably some x10kOhm). When the blade is hit, the Impact sensor - which is a flexible wire inside the green housing - touches the housing, which is in turn connected to GND. So while the Impact signal normally measures Vdd, upon impact it's pulled down to GND for the durations of the hit.
Here I sketched how it looks like in the inside of the blade:



In order to conduct when the signal level is low (GND), I needed to use a p-MOS transistor, which has a threshold volage close to GND. Due to the fact that the Vdd of a Hasbro FX is ~3.7V (4.5V theoretically, but it's never going to reach that level with the batteries), it has to be ensured that the Transistor is fully on even with a weak Level, so I wanted a p-MOS with a threshold of around -1V, finally my selection fell to IRLML6402TRPBF from International Rectifier (my Boss would kill me if he knew I made advertisement for a competitor...). As can be seen from the pic, the gate of the p-MOS is connected to the solder point called Impact, the Source goes to any of the LED segment positives (from which the FoC LEDs will draw their currents), the Drain is connected to the positive of the FoC LEDs, whose negative is connected to GND. Between GND and LED- you could insert a resistor limiting the LED current, but you may also opt to overdrive your LED without adverse effects for the duration of the clash for higher intensity.

On this pic you can see how much space this circuitry takes up (nearly none....)


If you want to do the same trick with a converted Hasbro featuring a single high-power LED (Cree, Tri-Rebel etc.), the same applies, you need to wire the clash sensor similarily, but intead of what I did to solder a string of FoC LEDs, you would probably want to use of the the LED dice as a FoC LED.

I made a small video showing the lightsaber after the conversion, I still need to find a decent Video converter to reduce the size, but I will post it once ready.

I hope you liked the short tutorial and looking forward to your Feedbacks!
Cheers: Andras

[Obi1]

...now I found that Video converter, so here is the short demo of the lightsaber featuring the FoC-like effect:

[clahey83]

good job! I think im going to use this technique on my daughter's first saber.

[Obi1]

Great idea, kids love lightsabers, even more when if flashes. BTW, I tried this technique first on an Ultimate FX, because the principe of the Impact/Hit is the same.

Do you plan to make a LED-string saber or one with HP-LED? Will it be an Hasbro conversion or a custom saber?

[clahey83]

im planning on using an econo Hasbro board. shes almost 5 so I need a board that will turn itself off if she sits it down and walks off lol. its going into a HP-LED saber (string blades dont like kids very much lol)

[dgdve]

Terrific job on this!

Thanks so much for sharing! So cool

[Sunrider]

Cool. Are you using a resistor to limit the current on this setup?

[Obi1]

If you meant the FoC LED(s), not, there I do not Limit the current, I use the full voltage of the 3 batteries on the 1 yellow HP-LED at the base of the LED-string and the ~30x3mm red LEDs along the blade. For the duration of the clash the overvoltage will not hurt the LEDs.

[Sunrider]

So I'm guessing that the 3 AA batteries come down to a lower voltage when the FoC kicks in. So the load on the batteries brings the voltage into the safe zone when it flashes? You could also do a series parallel wiring with the leds in pairs for battery packs that would maintain voltage better, like Li ion packs.