Adding Digital Inputs to Stargate


Senior Member
Looking ahead I can see that I will be running out of digital inputs on my Stargate pretty soon so I need to start thinking about the best way to add some more. The most popular method seems to be to install a CADDX alarm panel and use the alarm zones as general purpose inputs, but before I go down the road of installing a whole new hardware platform I had another idea...

I have a whole bunch of unused analog inputs and I was wondering why I couldn't just put a cheap relay at each one of these that would switch the input from ground to +5V when activated. The relay coil becomes my digital input and I get to keep everything on the base Stargate hardware platform. Is anybody doing something like this? Is there a downside to this approach that I am overlooking?
I think a better idea would be to put the analog channels to good use!

You could wire-up an R-2R ladder (D/A converter) and get many digital inputs per analog input.

More later... ;) Laundry calls...
This circuit will give you as many inputs as you want to wire, but, is limited by the resolution of your analog input.

Courtesy of Google, here is info on a four-channel version.
Cool idea! If I assign flags to each digital input I create, I can just watch for a change in the analog value and trigger a routine to reset the them accordingly. I'll have to set up test circuit and give it a try!