Schmitt Trigger

Welp, after talking with some smart guys on forums.parallax.com, it looks like the Schmitt Trigger feature on the SX is going to allow me to get rid of my 74HC132 that I’ve spent at least a couple hours messing with. It’s no big deal —- I’m glad to see it go!

The object of the game for me is the simplest possible circuit, lowest number of components, and so this will help. Turns out you have to simply enable ST_C on the appropriate bit that corresponds to the PORT C pin you are using for input.

I’ve already modified my code to use interrupts now — they are a heck of a lot more reliable in terms of timing than counting instructions etc. Much easier. I’m still running into an issue that I haven’t figured out exactly how I’m going to solve it.

The issue, loosely, is that I want to lock the start of interrupts on the first transition to 0 after receiving a bunch of data. See, initially, I don’t enable them until I receive a 0 — but after I get data, then I need it to go back to this initial state. It’s not easy if you see my code. Maybe there’s a variable I can set to zero?

The picture for today is the cool breakout board I bought from Winford Engineering. They make prototyping with db25 connectors a piece of cake.

Winford Engineering breakout

About the author

keith

Amateur Electronics Design Engineer and Hacker