Analog signal through I2C expander

Hi there guys and girls

I have now reached the limits of analog IN pins of my Arduino Mega and the project needs redesigning.

I have 20 temperature sensors now that need to be read (thermocouples), and was thinking of designing the project around I2C now.

Has anyone of you used MAX504CPD-ND (digikey number) 10 bit analog to serial converter with I2C?

I do not want to buy 20 pcs of those as it will add $60+ to my budget :frowning:

Any clever ideas to read my 20+ analog inputs to I2C?

David.

I think I have come up with a solution that is not too expensive for me.

I might use two of those I2C 20-I/O expanders:
CY8C9520A-24PVXI

One I2C is set up to turn on transistor to supply each of my Instrument amplyfying circuit 5V, thus I turn on and off each temp sensor. then I just connect the output of the Instrument amplifiers together in 1-3 groups to 1-3 analog to serial converters (MAX504) connected to the other I2C expander. Then it is just to read the no.2. I2C values.

Does this sound too crazy? :o

David.

http://code.google.com/p/multidisplay/wiki/TypKThermocouples

Have a look here...

How about just adding an analogue multiplexer (or two) in front of the arduino's analogue pins?

http://www.arduino.cc/playground/Learning/4051

thanks, will do... Would like to do custom I2C although :)

David.