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4hv.org :: Forums :: Tesla Coils
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MIDI Problem

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Graham Armitage
Fri May 24 2013, 11:37PM Print
Graham Armitage Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
Got an interesting MIDI problem that is similar to an earlier thread with one difference.

The DRSSTC is fed a signal via fiber from a MIDI controller (in a metal enclosure). The Laptop is unplugged, running on battery (as plugging it in exacerbates the problem). The laptop is connected to the MIDI controller with a USB-MIDI shielded cable. The whole control center is about 15ft from the coil.

Everything works really well, until there is a heavy ground strike, and the MIDI note hangs. There is no problem unless there is a ground strike. I am reluctant to shield and ground the audio electronics as that could potentially bring high voltage spikes too close to the computer. So two questions really..
1) Why is it only the ground strike that causes the notes to hang - ie. what is happening electrically to cause this?
2) How do I effectively protect the laptop etc from the coil influence?
Thanks
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HV Enthusiast
Sat May 25 2013, 12:40AM
HV Enthusiast Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Where is exactly is the ground strike occuring?

When you have an arc that strikes ground somewhere, there are a lot of peak currents that can induce a large amount of noise. For example, if you have a secondary strike that hits the wall or ceiling, that current has to return back to the base of the secondary, so it will do everything in its power to find a return - through the walls, nearby electrical wiring, etc...

I always use ground strike targets that are tied directly to RF ground of the secondary. This way, when the coil strikes one of these ground strike targets, the current returns directly back to the secondary and i somewhat control where those currents are going.

So if you get a ground strike, you could be inducing noise into your audio and MIDI electronics and its just interfering with the MIDI stream.

Without knowing more about your set-up, its kind of difficult to diagnose your problem.

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Graham Armitage
Sat May 25 2013, 12:55AM
Graham Armitage Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248
I understand it;s difficult to diagnose remotely frown

I have the grounded objects connected to the base of the coil, but it happens when hitting the strike rail. I suspect that it's actually the laptop that;s picking up something, because the MIDI program will lose the USB port it was using. If I move the laptop even further back it seems to be better.

I am actually interested in the electrical signal from a ground strike - if you say it generates all sorts of noise, then that could explain why the laptop might pick up something and screw the USB up. I believe the laptops are very sensitive to this sort of thing.

Thanks - this is helpful.
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plazmatron
Tue Jun 11 2013, 10:27PM
plazmatron Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Bushman wrote ...

Everything works really well, until there is a heavy ground strike, and the MIDI note hangs. There is no problem unless there is a ground strike. I am reluctant to shield and ground the audio electronics as that could potentially bring high voltage spikes too close to the computer. So two questions really..
1) Why is it only the ground strike that causes the notes to hang - ie. what is happening electrically to cause this?
2) How do I effectively protect the laptop etc from the coil influence?
Thanks

1) Just a guess, but but as easternvlotageresearch suggests. It is likely that it interferes with the midi signal. I have had a similar issue (not involving ground strikes) where if the midi signal is interrupted after the microcontroller starts playing a note, the microcontroller doesn't revieve the note-off message (or note with velocity 0 depending on your midi device)
The best way to mitigate this situation would be to code for it. So if a note lasts for > x ms , turn it off.

2) I use a toughbook for mine, with a Magnesuim case, but for standard hardware, distance is your friend!
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