Zero Crossing Detection

Hasan

Hi,
With background in CS, I have been working with enterprise Java for the past five or so years. Now I am getting back into my true passion, hardware design and Micro Java (MIDP). I came accross Javlin and bought the starter kit immediately.

After going through the manual, as my first project, I wanted to build a home control system based on Javlin and X10 protocol. I wanted to base my design on the ideas in application notes by Microchip, "Interfacing to AC Powerl LInes" and "X10 Home Automation Using the PIC16F877A". PIC can be made to detect zero crossing by connecting AC line directly to an I/O pin (thru and resistor). The input proectection diodes at the pin also do the voltage limiting. PIC can, then detect the edges and so the zero crossing. This is brilliant because only one external passive component is needed.

Now the question is, does Javelin have the protection diodes at its input pins? Can I do the same type of simple design to detect zero crossing with Javelin? The manual I have doesn't give this kind of specs. I could use the ADC VP too but I liked PIC's approach better.

Thanks for any help.

-Hasan

Jon Williams

Yes, it does, but you're no longer running machine code and running interpreted Java may not be fast enough to detect zero-cross points reliably. If you do decide to proceed, strap on a couple 1N914 diodes just for safefty, and by all means proceed very cautiously. A PIC chip is cheap -- a Javelin module is not....

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Jon Williams
Applications Engineer, Parallax
Dallas Office

RussR

I'd even go so far as to say use an isolation transformer. any low current low secondary voltage would do. Bad form to connect directly to the AC line!

Russ

Hasan

Thanks, I took the advice. I will use a transformer on the transmit side which has the javelin brains but I'll use a cheap PIC16F84 on the receive side connected directly to AC since the circuit must fit on a very small pcb.