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Registered Member #2677
Joined: Mon Feb 08 2010, 03:06AM
Location: Palo Alto, California, USA
Posts: 64
Hello all, As part of my current tesla coil project (which I hope to complete soon) I am developing an arduino based interrupter. I have written the code for the arduino and I have a general idea of what the rest of the circuit will consist of. The arduino feeds into an HFBR-1412 fiber-optic transmitter. A description of the circuit is included in the code which I derived from one of the examples provided with the Arduino IDE. It would be much appreciated if someone a bit more seasoned in programming Arduinos could review my code and identify any potential problems. I intend to keep the code public so that others besides me can benefit from it. The code is at http://ubuntuone.com/p/1A71.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
Is there any reason you're using an arduino for this? It looks like your code is pretty much emulating a 555 timer interrupter. While there is technically nothing wrong with this, a 555 is far less likely to fail near a tesla coil than an arduino is. Also, if it fails in the wrong way (such that the output of the interrupter is locked high - and I have had this happen, it's effectively a garunteed bridge burn out) it would be unfortunate.
My solution to this was to make a one-shot pulser as the output stage, which is fed by microsecond pulses from a microcontroller. It can be setup in such a way that even if the input to the one-shot from the microcontroller is held high indefinitely long, there will still just be one pulse at rising edge to the coil and nothing bad happens except requiring you to reboot the frozen controller.
The only drawback to my solution is that you can't have the microcontroller change pulse-width to increase the width of bass notes so as to keep their wattage up and their spark intensity high. This could be solved by using a digitally controlled resistor, however I have not bothered to attempt this yet.
Registered Member #2677
Joined: Mon Feb 08 2010, 03:06AM
Location: Palo Alto, California, USA
Posts: 64
The reason I am using an arduino is so that I can eventually program it to run specific sequences of frequencies to do things like playback musical scales as well as possibly MIDI input. I do like the idea of a digital potentiometer to control pulse width as I was thinking about replacing the pots with momentary push-button switches that would cause the Arduino to raise or lower the BPS or on time by a pre-set increment. How would I determine what the on time will be given the value of the capacitor and what resistance level the potentiometer is set to? Thanks for your reply, by the way, I was concerned that it might have lock-up issues.
Registered Member #2288
Joined: Wed Aug 12 2009, 10:42PM
Location: Cambridge, MA
Posts: 179
You can calculate it as follows: The voltage across the capacitor should follow 1-e^(-t/(R*C)), and you can solve for the time at which that voltage crosses the schmitt trigger level, which is I think around 2.7V for 74 series logic. I don't remember the exact capacitance I used but I'm pretty sure it was around 1-10nF.
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Arduino DRSSTC Interrupter
