ditz@ECN.PURDUE.EDU (Michael R Ditz) (02/19/91)
I am working on an X-10 based home control system for a senior project. We have decided to make our own X-10 transmitter for specific reasons. The part that I am having trouble with is the zero-cross detector. What we need is the AC line as input, and some "nice" voltage output pulse at each zero-cross. One of the problems is that a transformer CANNOT be used, because it will shift the phase. I would GREATLY appreciate any help on how to do this. Thanx!!! Mike (ditz@en.ecn.purdue.edu)
ftpam1@acad3.alaska.edu (MUNTS PHILLIP A) (02/19/91)
In article <9102182138.AA22294@en.ecn.purdue.edu>, ditz@ECN.PURDUE.EDU (Michael R Ditz) writes... > >I am working on an X-10 based home control system for a senior >project. We have decided to make our own X-10 transmitter for >specific reasons. The part that I am having trouble with is the >zero-cross detector. What we need is the AC line as input, and >some "nice" voltage output pulse at each zero-cross. One of >the problems is that a transformer CANNOT be used, because it >will shift the phase. I would GREATLY appreciate any help on >how to do this. The best method I have found is to use an optoisolator. I like to use an AC input device like the H11AA4 with about a 10 Kohm series current limiting resistor on the input side. I tie the output emitter to ground, and collector to +V thru a pullup resistor. The voltage across the transistor will be a recified sinusoid, which can be squared up with a Schimdt trigger gate like the 7414. Another possibility is to use a logic output optoisolator with a small bridge rectifier on the input. Philip Munts N7AHL NRA Extremist, etc. University of Alaska, Fairbanks
whit@milton.u.washington.edu (John Whitmore) (02/19/91)
In article <9102182138.AA22294@en.ecn.purdue.edu> ditz@ECN.PURDUE.EDU (Michael R Ditz) writes: > >I am working on an X-10 based home control system for a senior >project. The part that I am having trouble with is the >zero-cross detector. What we need is the AC line as input, and >some "nice" voltage output pulse at each zero-cross. One of >the problems is that a transformer CANNOT be used, because it >will shift the phase. Actually, a transformer would do nicely. They don't shift the phase unless you're saturating something. A useful approach is to use two phase-shifting networks, one leading, the other lagging, like: |\ | \ AC hot------VVVVV-----+----||-----+-----| >-----output R1 | C2 | | / | R2 > |/ C1 = > | > AC neutral------------+ GND Use R1*C1= R2*C2, make R1 much smaller than R2 (factor of a hundred?) so that the two RC pairs are both lightly loaded by the next stage, and try for time constants large compared to 1/60 second (because you NEED some attenuation here). The amplifier shown could be a CMOS Schmitt trigger, or comparator; 'GND' can be any convenient DC bias point (if you use +5 regulated power, +2.5 V would be a good choice). I assume that you are using NONisolated power for your logic circuits; else that amplifier up there will have to include some isolation. John Whitmore
jim@rwsys.lonestar.org (James Wyatt KA5VJL) (02/19/91)
ditz@ECN.PURDUE.EDU (Michael R Ditz) writes: >I am working on an X-10 based home control system for a senior >The part that I am having trouble with is the >zero-cross detector. What we need is the AC line as input, and >some "nice" voltage output pulse at each zero-cross. One of Back when I was working on a computer-controlled light dimmer, I found a simple optoisolator with a *large* dropping resistor worked best. The output was conditioned by a pull-up resistor into a Schmitt trigger and it produced a nice square wave (with an occasional glitch). We fed the square-wave into a PLL, so a minor spike or two didn't hurt us. If you need a pulse, try feeding the output into a short delay (sets your pulse width) and feed the input and output of the delay into an XOR gate. The output will be active from the time the square-wave changes to the time the change makes it through the delay. (You might use the rest of a 7414 schmitt tigger for the delay). Hope this helps - jim ---- James Wyatt (KA5VJL) - Standard disclaimer applies... (H)817-595-0571 {letni.lonestar.org,merch.tandy.com}!rwsys.lonestar.org!jim (W)817-390-2864