How do I detect a polarity change on an input?

[CocaColaKid]

The <> just means the two values are not equal.

[Darrel Taylor]

Right, it's not equal to.
By means of being either Less Than or Greater Than, just like >= would be greater than or Equal to.

It's initialized to 255 to make sure it always triggers on the first pass.
If it were left at 0 (assuming there's a CLEAR statement), and the first Request was also a 0, then the code wouldn't execute and the output state would be left Undefined.

hth,

[jessey]

Very Clever Darrel,

Thanks for the explanation and the code, I totally understand it now. It took me a few minutes to fully get it and once I did I could see with-out a doubt that it's fool proof.

Thanks Again
jessey

[ardhuru]

Jessey, although your original query has been answered, I thought I would add my opinion as well.

When you speak of the X10 transmitter I assume you are referring to an X10 RF transmitter, right?

In which case, why not get rid of the X10 remote altogether, and drive an RF transmitter module directly with your 877? The RF protocol used by X10 is well documented (its actually the NEC IR protocol) and I could send you the URL(s). Besides the hardware being much simpler, you could send as many different commands and addresses as you wish without having to add more transistors.

Regards,

Anand

[ardhuru]

Forgot to add, there are readymade basic snippets on the web that directly let a stamp drive an X10 firecracker as well; would achieve the same objective you seek.

Regards,

Anand

[jessey]

Thanks Anand,

I've been away visiting with a friend without a computer (hard to believe now a days). Now that's something that I'd definitely be interested in investigating. I surely would appericate receiving the URL's if you could please send them to me.

Thanks Again
jessey

[ardhuru]

Hi Jessey,

To begin with, here's Dave excellent page on the X10 RF protocol http://www.arkis.net/rf_protocol.htm.

This would give you a pretty good starting point.

The other approach would be to use a CM17A (Firecracker) module; this would eliminate the need for a separate RF transmitter. Theres loads of basic software available to drive it; one such page is at http://www.awce.com/firecracker.htm

Hope this helps!

Regards,

Anand