Hasbro Sound with Mosfet

Hello folks,

I am not certain this will be answered or not. Either way here goes:


I was tinkering around with a hasbro sound and wondered why transistors are used in the upgraded wiring instead of mosfets.

So I hooked up a mosfet in the typical fashion to the speaker negative and used a white cree xp2... It was getting too much juice (full power not usual on speaker gnd). I resistored it.

Now when the power is turned off, the led with thr mosfet is still on. It slowly turns down.

Is this because the mosfet gate takes such little current that it is still being utilized?

or does the mosfet itself act as a capacitor and has a residual charge?

anyway to eliminate this issue?

thanks.


PS. the issue is livable, I am attempting to use 3 mosfets on a obiwan clonewars sound board and a tri-cree. I have 3.7v liion capable of 4 amp discharge. Because voltage drop across a mosfet is less than the tip42c....

I believe the term you are looking for is "Pull-down resistor". A resistor is used in conjunction with the MOSFET to eliminate this issue. It's a little beyond my area of expertise, but a little Google-Fu should get you the answers you seek.

There's an article some where "you can have my TIP42 when you pry it out of my cold, dead hand." that covers this. I'm not an EE by any stretch, and I could certainly use an education on the topic, but I use TIP42/41 all the time because it's just easier. MOSFETs are nice because you can use a tiny SMD, but unless you are building a PCB...

Thanks for the responses,

I know nothing, just what I play around with and research.

I think I understand the basic concepts of transistors and mosfets, and that mosfets are better utilized in conjunction with microcontrollers.

I will research what you mentioned silver serpent .

The main reason I am looking at this option is because I was able to fully power the one Xp2 cree die off the speaker ground (as if PWM...) while the 3w single die led still ran off the LED grounds...

I'll see where it takes me.

*edit quick google fu-has led me to the answer. Pull down resistors as mentioned by Silver Serpent*

http://hackaday.com/2015/08/17/you-c...ld-dead-hands/

If you don't feel like researching parts and then wiring up your own mosfets and resistors, there's an option in the TCSS store. http://www.thecustomsabershop.com/Po...r-20-P652.aspx

Silver,

I pulled the trigger and got the NBV4 and a couple of xtenders for other builds.

The NBV4 specs sound awesome. I am excited.

Quote:

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Originally Posted by Whosle

Thanks for the responses,

I know nothing, just what I play around with and research.

I think I understand the basic concepts of transistors and mosfets, and that mosfets are better utilized in conjunction with microcontrollers.

I will research what you mentioned silver serpent .

The main reason I am looking at this option is because I was able to fully power the one Xp2 cree die off the speaker ground (as if PWM...) while the 3w single die led still ran off the LED grounds...

I'll see where it takes me.

*edit quick google fu-has led me to the answer. Pull down resistors as mentioned by Silver Serpent*

http://hackaday.com/2015/08/17/you-c...ld-dead-hands/

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If you use the MOSFET off the speaker ground, do you still get blade shimmer AND full brightness?

SA22C,

I have since aborted the use of a mosfet for this application. It requires extra resistors which takes up more space.

If you use one tip42c on the speaker line, and one tip42c for the LED (wired to 2 die), you can get 2 die at full brightness amd one die(from speaker tip42c) with flicker(shimmer).

Thats the best I could do. I tried a mosfet off the main LED leads on the board and the first time I tried it on a breadboard it didn't need pull down resistors, after it was all wired up, it was on when the board was off, and off when the board was on.....

Anyhow you could try buying 2 power extenders from TCSS and hooking one up to the speaker line and one up the LED line.

I will post a better video of the flicker on my Ghetto-flex thread in the gallery.

I think a good quality liion 3.7v is necessary as well. This is only on the Obi-wan clone wsrs with dvd toy board.

Quote:

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Originally Posted by Whosle

SA22C,

I have since aborted the use of a mosfet for this application. It requires extra resistors which takes up more space.

If you use one tip42c on the speaker line, and one tip42c for the LED (wired to 2 die), you can get 2 die at full brightness amd one die(from speaker tip42c) with flicker(shimmer).

Thats the best I could do. I tried a mosfet off the main LED leads on the board and the first time I tried it on a breadboard it didn't need pull down resistors, after it was all wired up, it was on when the board was off, and off when the board was on.....

Anyhow you could try buying 2 power extenders from TCSS and hooking one up to the speaker line and one up the LED line.

I will post a better video of the flicker on my Ghetto-flex thread in the gallery.

I think a good quality liion 3.7v is necessary as well. This is only on the Obi-wan clone wsrs with dvd toy board.

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Thanks for the tip. I tried wiring the white led to the speaker using a tip and the two blue dies to the led negative with a second tip, but the white was so weak it was washed out by the two blues.

Oh well, no big deal. For the money, the hasbro board is a great solution.

Thanks for the reply!

The white may be washed out, but when you swing or clash it will get brighter.

As well, if you have the one flicker led wired to the speaker , it will help disguise the flash on and flash off.

When you clash it will clash white.