An alternate way to do the LED light up on activation mod?


I’ve been talking to a friend about the method of doing the LED light up on activation mod via the hex inverter.

According to him, there is another easier method that will work just as well, and potentially not need an external battery.

He’s good with electronics and building analog circuits, but not familiar with controller pcbs, and I’m not versed enough electronics or building circuits to give him the specifics of how the Cthulhu or 360 pad works. As far as he knows the pad should be able to power the LEDs on it’s own via the USB, but maybe someone here knows otherwise.

Basically his method uses PNP transistors and a couple resistors of specific values instead of the hex inverter.

What I’m hoping is that some of the electronics gurus on the board will let me know if this method would work.

He would like to know what the benefit of using the hex inverter would be as opposed to using PNP transistors which can be easily found at Radioshack (while the inverters need ordered for most people).

Here is the schematic:

Any thoughts or input would be appreciated. Thanks.


Quick question, what’s the light up on activation mod?

LED ON when the button is pressed? As in a light up mod for your buttons?

right now as he’s got it, when you press the button (close the circuit), the PNP will turn OFF, and the LED will turn off. NPN’s turn on when biased, PNP’s turn OFF (has to do with the internal PN junction).

Also, the PNP is backwards I think, the arrow is supposed to go from the VCC side (collector) down to the base, not from emitter to base.

Toodles confirms.

Also he’s right, you’re replacing a cheap part with a more expensive (and tougher) implementation, I wouldn’t recommend going this way.

Again also, that’s badass toodles

Another thought, real estate. Not sure if you care but 6 transistors + resistors takes up more space than a single IC… by a lot. Again, with a fightstick that may not be an issue but you’ll have to get a PCB from radio shack to make it somewhat clean as well…so don’t forget to add that into your shopping list.


Nope. Well, I mean it will work as is (or something close to it. Isn’t that the wrong transister though? Meh, doesn’t matter.) but:

  1. Most worthwhile pcb’s use a common ground. That schematic assumes a common High. Not too big of a deal since the schematic can be switched around to work on a common ground setup without any additional parts.
  2. For a six button stick, you’d be replacing a single $0.25-$0.50 chip with six transistors, six resistors (the ones between the pull up/pull down resistor and the base of the transistor), and probably 6 diodes as well.

The funny part? The schematic shown above is the implementation of a non-inverting buffer. On a common ground setup, it’d have to be redone to be an inverter. Or you can just get the inverter from the get go for better performance, less wiring, and less impact on the original circuit.

(Or just sit tight for a quick spell. An LED board has already been made with kaytrim and I working on getting the code setup. The result will be FAR FAR cooler than just ‘on when pressed’. )

Edit: In case anyone thinks Im full of shit :slight_smile:


Thanks toodles, I’ll run it by him and see what he thinks (because I don’t know nearly enough about what you’re talking about to respond to it correctly).

As far as price though, I can get 6 transistors from radioshack for $1, along with the needed resistors for $2.

So total cost this method would have been $3 plus some tax. But digikey you’d have to pay at least $5 shipping on the parts which would be a few bucks also. Not a big difference, but if you’re doing a lot of sticks it adds up.

I’m sure when describing to him the way the pads worked I left out some important parts of what you’re saying, so I’ll talk to him and let him know.

edit That LED board looks awesome btw. I just need my LED mod now:sad:


Ok, this is his response (fast response because he works with me, lol).

It does invert because it’s a PNP not an NPN and would be off when the input is high and on when the input is low … inverting. You can get a chip and make it just as small as his. Wouldn’t need the the diodes he is talking about … your using Light Emitting diodes. No current will come back from them. Sure it is 10 ns slower in it’s switching but I’m sure no human will notice that! :wink:

For the record, I’m not proposing this as a better way to do things, just got to talking to him and wondered what the benefits to using the inverter chip as opposed to something like this would be.


I did my light-up LED mod with the method andywarne posted in the other topic:

It should work just fine if you’re doing this to a 360 or PS3 PCB. No components other than wire, LEDs, and resistors necessary.


I’m not trying to or going to argue. It’s easy to see what he’s trying to do, and yes, it (the idea) can work. If you’re trying to avoid using the chips, and are using a common ground pad, just wire the resistor and LED directly like drunkninja suggests.

Benefits of using an inverter over this method:
Smaller size
Less interference from the original pcb’s signal lines (less current drawn from the signal line, less influence on the voltage of the signal line) May matter for some pcb’s, but won’t matter for most.
Easier and less wiring



I’m really just trying to learn how all of this works, so I’ll probably get all of the parts for each method and mess around with all of them.


2 q’s:
can you set multiple LEDs to a single button?

and can you set multiple buttons inputs to light up a single button?


Yes and yes. Although, the multiple buttons to light up a single button require different chips to do. (two buttons would require a 2 input NOR gate, three would require a 3 input NOR, etc.)


yes u can set multiple its no problem …


Toodles, you’re a friggin electronics GENIUS. You make my brain fart just trying to keep up with the lingo =)


do want

Put me on the list now ill take 2!


Ohh… I’ve worked with MEGA8’s before, this should be really interesting. Looking at the pinout on the board, I’m guessing it’ll have the ability to light up different moves (like a keyboard that lights the keys to play)? Any timeline at this point for production? If you’d like another head looking at the code, I’ve got at least a semester’s experience (we used several of those chips in my embedded systems class in college) and would be willing to give up some free time :wink:


Super interesting. How exactly would this work? I’ve been toying with having lighted buttons on my 1st (wireless PS3 only) stick, but if this will make things easier I may wait until I build a second one.