This blog post is about the very long process of how I came to make a box that could dynamically dim AC bulbs via computer control. The main purpose being to react to music. View this as a documentation on how I came to make this box, and my thought process throughout. I will be providing code, and some schematics, and I hope other beginning hobbyists will find this post useful.
(If you’d like just to find out about the box, simply start at page five)
First, a brief history.
My desire to make lighting that would react to music largely began in late 2003. A Perfect Circle released their album, Thirteenth Step. Upon first listen of the song, Blue, I pictured a series of lights reacting to the music, and blue shifting upon the chorus line of “She’s turning blue.” At the time, the original Xbox modding and hacking scene was huge, and I had jumped onto the bandwagon. Prior to this, I soldered here and there, but had no real experience with electronics or hardware design. Nor did I know where to begin. I knew I desired the skills, but was still a hardcore n00b. I found datasheets at the time to be highly overwhelming. During this same period of time though, I was learning tricks here and there mainly due to the large number of hardware hacks being performed on the Xbox.
As the years went by, I was doing IT work, and learning about other technical skills, but I was slowly putting my (limited) electronics hobby to the back burner. Flash forward to 2007, and I read a blog post of how Xbox-Scene moderator, Twisted Symphony, had made a circuit that would allow the use of a Sega Saturn pad to play Xbox 360 games. As I was a huge fan of the Saturn pad, I wished to replicate this design, and to possibly improve on it.
Twisted Symphony, as I would come to learn, had used a PIC16F690 Microcontroller to break out the Saturn controller’s serial data into Parallel data that was fed into an xbox 360 pad. I began to research PIC Micros, but ultimately ended up buying just a breadboard, and playing around with simple circuits due to my limited disposable income at the time,.
Then came February, 2008…..
Hi.
Does the transformer induce some phase (delay) to the zero cross detection?
Juan, I’d imagine the Sine Wave looks the same after being stepped down, only with less power, so I don’t think a delay is being caused here, or the wave is being pushed out of phase.
The wave becomes rectified and drives a Transistor that in turn inverts the signal into a a square wave. i.e. when voltage is 0, the transistor passes no power, and a pull up drives the interrupt high. What I believe is happening is once the wave hits a low threshold, say 4v, for example, the transistor no longer functions, and the interrupt is triggered. I’d like to find a solution to this.
Hope that helps.
I know this has been idle for a few months but just to give a possible solution.
You have a processor, which allows you more flexibility that a transistor circuit monitoring a full wave rectifier.
If you use a single separate diode as a half wave rectifier,with some resistors you’ll get a square wave at the line frequency, that you could read with logic input.
Now if life were perfect,you’d be set, because all you would have to do is monitor that input for an edge. Rising or falling. That would be a zero crossing. It may even work just that simple. But possibly there is line noise on the AC that would give you several as the signal is near Vinputhigh. There is also a symmetry issue, where voltage crossing would be different on one phase from the other. Its the kind of thing you’d use a Schmidt trigger to read if you were using pure logic.
This is where the processor comes in. You can calculate how deep into the wave form the input crosses Vih, and when it will crass back again on the way down. From there you can calculate where the real zero crossing is.
With further elaboration you should be able to use that data make a phase locked loop in software that locks into the 60 Hz signal of the AC line. Using that as a time base, then you can determine your triac firing times.
On additional thought, you can really factor out the asymmetrical aspect of the half wave detector. Whatever Vih is, the peak of the AC powerline waveform is going to be half way between the rising edge and the falling edge. Likewise the nadir of the low part of the cycle will be half way between the falling edge and the next rising edge.
This PIC has a timer. So if (after deglitching) you take the times of the rising and falling edges, you should be able to calculate where the peaks are, and thereby the zero crossings.
I’d probably set it up so that a timer caused an interrupt when it rolled over, intending that to be a zero crossing. Reloading the timer count should take into account the error based on the the expected peak times. If the peak is not at 1/4 of a cycle, and the low at 3/4 of a cycle, calculate the error, and add that in when setting the timer count back 1/2 a cycle in the interrupt service routine.
You can even use an initialization process at the start of day to figure out how many timer ticks a cycle is, and not worry about an absolute scaled time base. just get an average for a few cycles.
Therefore with a bitof deglitching, you should be able to know
You can use another optocoupler on the transformer line in place of the transistor circuit instead. Look up the 4N26. The internal diode will half rectify the wave and the transistor will cause a more precise square wave you can base your timing from.
You must be Psychic. The last comment here was over a month ago, and I JUST had gotten done purchasing it’s sister chip, the H11AA1 when you commented. I was researching this earlier. The Renard PIC controller uses it, and I think I’ll adapt it also.