Stargate SG-IP A/D Converter


Hi all,

I am beginning to add analog inputs to my Stargate SG-IP and the following is what I have found:

I believe that I may have a bad A/D converter or converter reference on my SG-IP motherboard.

I am powering my light and temperature sensors from an external +12 volt power supply.

I have the return side (-) of the sensor power supply tied to the Analog Ground on the motherboard.

I have one temperature sensor tied to A/D input 6 and it is reading approximately 1.37 vdc at the A/D 6 input with respect to Analog Ground.

When I read the temperature sensor input when it is not hooked to A/D input 6, I get a value closer to 1.57 vdc.

I have the Stargate I/O enabled in the IR and I/O window.

I have defined A/D input 6 as AD6 with a Gain=1 and an Offset=0 as the temperature sensor puts out 20mv/degree F.

When I do an A/D read to see the raw and converted values, I just get the value 255 when it should be 1370mv/20mv= ~63.

It seems like the A/D converter is loading its inputs.

When I use the Mega Controller to read AD6 in the Analog widow, it shows a value of 255 like the raw and converted values window in the Analog I/O define window.

As a matter of fact, all of the A/D inputs that are floating and not tied to ground or to an analog input, read 255 when they should be reading random floating values between 0 and 255!

Unless I am doing something wrong with the programming of the A/D input definitions, I believe that either the motherboard A/D converter or the converter references is bad.


An easy way to check would b to put a jumper between analog ground and 5 VDC ground. Then put a jumper wire between one of the analog input terminals and the other analog ground terminal (there are 2). You should get a reading of 0. Then if you move that wire from analog ground terminal to the +5 VDC terminal that should move you back to 255. If there is no change in the input when using this internal reference source then you may have a bad analog chip and it is time to call tech support.
Hi upstatemike,

Thanks for the input. Much appreciated.

What you have suggested was going to be my next step.

Jeff at JDS thinks that it is probably a bad A/D converter.

My Stargate is only two months old and this should be covered under JDS's warranty.

Fortunately the A/D converter is in a socket and can be easily replaced with a pair of IC pullers and a ground strap both of which I have and use occassionally for repairs.