+/- 10 input ADC

bennettdan

Hello
I have a need to read a -10vdc to +10vdc two wire signal and was looking to see if anyone knows of a ADC that can read it?

groggory

I'd adjust your references so you're talking all in positive voltage.

The way you do that will depend on your exact circuit. This will almost definitely add a little noise, but no big deal.

Tubular

Parallax sell the MAX1270 in DIP form which is useful for this kind of thing.

I also use Max1032 and Max1302 for more precision but these are harder to get and prototype with.

Parallax really should advertise the fact the MAX1270 ADC can do bipolar inputs on that product page. Its a big selling point.

bennettdan

Thanks Tubular I will look into the MAX1270 I have read through the datasheet it only needs a single supply and allows +/-10vdc input. I think you hit it on the head with this one.
Do you happen to have any sample code to setup the MAX1270 with the Prop for +/- input?
Thanks again

pjv

Bennettdan;

You can also do this directly in the Prop without any external chips; only two resistors and a small cap. I believe there is an appnote about Sigma Delta A/D.

The conversion results will be skewed due to a non-zero reference point, but that is easily dealt with by a simple subtraction. Personally I have not done this with the Prop, but many time with an SX processor with excellent results. I believe the Prop should also deliver good results, and the code to implement this will be less than the work required to interface to an external chip.

Cheers,

Peter (pjv)

Tubular

This code from the Obex should get you going...
http://obex.parallax.com/objects/513/