Stargate SG-IP A/D Converter

[TCIII]

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.

Comments/suggestions?

Regards,
TCIII

 

[upstatemike]

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.

 

[TCIII]

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.

Regards,
TCIII