Adding Digital Inputs to Stargate

[upstatemike]

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?

 

[TonyNo]

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...

 

[upstatemike]

OK, you definitely have my attention! What is an R-2R ladder and how many digital inputs will it give me?

 

[TonyNo]

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.

 

[upstatemike]

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!