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Registered Member #855
Joined: Sat Jun 23 2007, 05:25PM
Location:
Posts: 8
Hi Guys,
I have a 2 part question I was hoping to get some help with. I have been doing a ton of reading and I'm getting some stuff mixed up, so I feel like a need a human being to clarify some stuff for me.
I currently building Steve Wards 'MINI SSTC'
1) I was wondering if it was possible, by switching out the 555 timer circuit (the interrupter? Not sure what it would be called) with a micro controller I could make the coil play music.
2) Assuming it's possible, would I vary the frequency of interrupter pulses, or the duty cycle to make the corresponding sound frequencies?
Example.
I want to play 'Middle C' @ 261.63Hz
I set the duty to %50, Period = 3.822ms, on time = 1.91ms =off time.
Would that work? Would the sound change it all by changing the duty cycle but keeping the frequency the same? Meaning, can I drop the duty cycle down ~10-20% if I am having issues with heating?
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
You could do exactly that. You don't even have to go as far as an MCU, because it's an SSTC and you are not inherently limited by duty cycle like a DRSSTC. You could alternatively just use a simple zero crossing detector (like an opamp or even 74HC14) and put in regular audio and have it simply square it off so it can be used to turn the digital log on and off.
Don't get me wrong the MCU option will also work fine, I do it all the time with my DRSSTCs but only because I have to duty cycle limit. It's just not entirely necessary.
Your second question, changing "off time" or period will change the frequency of the sound the coil will produce. Duty cycle will correspond to power output. However it could be done by changing the duty cycle as well I suppose but this would give more of an AM modulated effect.
Registered Member #855
Joined: Sat Jun 23 2007, 05:25PM
Location:
Posts: 8
Goodchild wrote ...
You could do exactly that. You don't even have to go as far as an MCU, because it's an SSTC and you are not inherently limited by duty cycle like a DRSSTC. You could alternatively just use a simple zero crossing detector (like an opamp or even 74HC14) and put in regular audio and have it simply square it off so it can be used to turn the digital log on and off.
Don't get me wrong the MCU option will also work fine, I do it all the time with my DRSSTCs but only because I have to duty cycle limit. It's just not entirely necessary.
Your second question, changing "off time" or period will change the frequency of the sound the coil will produce. Duty cycle will correspond to power output. However it could be done by changing the duty cycle as well I suppose but this would give more of an AM modulated effect.
Hope this helps!
Never thought of putting regular audio in, that would be a lot less programming, haha.
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Hi Truant19, check out this schematic as you can see on lower right, the opamp and 555 timer to square up the audio waves. And I believe this schematic is also based on steves micro sstc, but could most likely also be used with the mini sstc.
Registered Member #855
Joined: Sat Jun 23 2007, 05:25PM
Location:
Posts: 8
Physics Junkie wrote ...
Hi Truant19, check out this schematic as you can see on lower right, the opamp and 555 timer to square up the audio waves. And I believe this schematic is also based on steves micro sstc, but could most likely also be used with the mini sstc.
That schematic is pretty much exactly what I'm looking for, but I am pretty confused by the audio circuit. I guess I could build in Multisim and try and figure it out, but if you know, do you mind giving me a brief overview on the operation?
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Sure, click the picture to see it larger. I drew this up in Autodesk Sketchbook, sorry for sloppy writing. But basically, you have your MP3 player (probably best not to use expensive ipod) and this is sending the sound waves to the op amp. if you have an oscilloscope you can see the sound waves if you scope the output of the op amp. These sound waves are being squared off by the 555 timer, again you can see the square waves if you scope the output of the 555. Then these square waves are sent to the gate drivers, just as your normal 555 interrupter would be. Hope that helps!
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Truant19,
Excellent questions, thanks for posting them!
One of the easiest ways to implement audio into your coil is to simply build a zero cross detector circuit. It works this way:
1. You have a keyboard and use a flute sound or sine synth sound or anything that outputs close to a sine wave for best results. You then feed that audio output (from the keyboard) into a comparator circuit which detects the zero crossing of the sine wave. At each zero crossing, the output of the comparator will trigger a one-shot circuit to output a fixed pulsewidth. The one-shot, typically just a 555 timer. Feed this output into your DRSSTC.
These are how the first DRSSTCs were modulated before MIDI came onto the scene.
There was a very brief article (basically just a one page handwritten schematic written by an Alan ??? i think) that used to reside on the hot-streamer website. It was dated from the 80's i believe and was used to connect a keyboard to modulate a vacuum tube coil. I'll have to see if i can find it on the Bert's mirror of the hot-streamer website.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
Actually, if you are looking for SSTC audio modulation - were you referring to a plasma speaker type reproduction (full bandwidth audio) or the buzzing audio tones commonly seen in DRSSTC audio modulation? If its the latter, then thats the zero cross circuit.
If its full-bandwidth audio modulation you need, then simple PWM of the gate drive is all you need. This can be done as simply with a single 555 timer IC or similar IC such as TL494.
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