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Audio modulation problem, DRSSTC

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LAN_403

zzz_julian_zzz

Sun Jan 15 2012, 03:08AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Using this schematic, I am having problem to my audio input(keyboard) once I put a note to this interrupter, my keyboard got stock multiple notes at the same time and it hangs up.. what could be the problem? =/ thanks in advance..

Daniel Kramnik

Sun Jan 15 2012, 05:30AM

Registered Member #3885 Joined: Sun May 15 2011, 12:47AM
Location: Newton, Massachusetts, United States
Posts: 94

You need your keyboard to be isolated from your Tesla coil's circuit, otherwise, it will go crazy. Add an optoisolator IC, or better yet, a fiber optic transmission system between your modulator and your DRSSTC's interrupter input.

Goodchild

Sun Jan 15 2012, 06:02AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

Isolation will help but only one thing with completely fix the problem, and that is to move the keyboard as far away from the coil as possible. My whole system is fiberopticly isolated and I still have that problem with my keyboard and small DRs.

I think it has to do with the sensor that is used to sense key pressure, it seems that EMI from the coil can trigger them very early. Also because it's a positive feedback loop the more keys that are trigger the more the coil outputs in turn making more EMI and triggering more keys. It's a scary cycle and one should take care to add some kind of limiting to there controller. Because I use MIDI it inherently limits to 2 notes and usually only results in me having to reset the controller.

Good luck

EDIT

I noticed after looking at your controller that you limit PW but not off time. It would be in your best interest to add a minima dead time to your controller to set a max duty cap on the output. IF you don't do this you could easily still get to 50%+ duty cycle just by playing lots of notes at ones or high freq notes or both!!!

zzz_julian_zzz

Sun Jan 15 2012, 02:07PM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

It would be in your best interest to add a minima dead time to your controller to set a max duty cap on the output. IF you don't do this you could easily still get to 50%+ duty cycle just by playing lots of notes at ones or high freq notes or both!!!

-how can i do that? do you have schematics which I can borrow? thank you daniel and goodchild for your astute observation.. Goodchild, you're one of my idols =)

Goodchild

Sun Jan 15 2012, 04:44PM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

zzz_julian_zzz wrote ...

It would be in your best interest to add a minima dead time to your controller to set a max duty cap on the output. IF you don't do this you could easily still get to 50%+ duty cycle just by playing lots of notes at ones or high freq notes or both!!!

-how can i do that? do you have schematics which I can borrow? thank you daniel and goodchild for your astute observation.. Goodchild, you're one of my idols =)

You already have a 555 limiting the on time, what is to stop you from using another 555 to limit the off time? Just invert the signal first send it into the 555 to limit it and then reinvert it on the output and hey presto you are limiting off time.

I also found this circuit a while back.
3651170986 15bb8acc52

This is basically just a another one shot type circuit. Because it limits on time you would have to ether inverter the signal first or reverse the polarity of the diode.

Hehe no one has told me that I'm there idol before, I'm flattered thanks

zzz_julian_zzz

Mon Jan 16 2012, 05:35AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

Goodchild,

will this be the whole new schematics you are referring to? this is to regulate only the off time, isn't it? but how about the on time?
thank you again Idol! =)

edit: Sir, my coil is now audio modulated, but having a problem when the note is weak(small volume) this tends to chop the output.. And i have to strum again my bass guitar louder to make a more lasting note but then it will chop when the note is getting weaker, (do i have to make a pre-amp?)

Goodchild

Mon Jan 16 2012, 07:07AM

Registered Member #2292 Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795

zzz_julian_zzz wrote ...

Goodchild,

will this be the whole new schematics you are referring to? this is to regulate only the off time, isn't it? but how about the on time?
thank you again Idol! =)

Umm aahh you need to move your triggering network that 1k and D1 to after the inverter, You may also have to play with the triggering network to get it to trigger on the correct edge.

If you want to limit both on time and off time you need to use 2 555 run it though one to limit off time then another (after invention) to limit on time. You may also consider dropping the 555's altogether and just using the inverter to do the limiting(like in the circuit I posted) much simpler. If I have time tomorrow I will throw your circuit in spice and tweak it a bit.

What you will probably want is actually a preamp with a high frequency rolloff so that is has less gain at high BPS. This will help to control power draw.

zzz_julian_zzz

Mon Jan 16 2012, 10:12AM

Registered Member #3964 Joined: Thu Jun 23 2011, 03:23AM
Location: Valenzuela City
Posts: 332

okey, thanks Idol! =D., will be waiting for your schematic, then I will compare what I did came up too..

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