Jacky,

Assuming you don't need anything else added to the data bus, you can do the following: (image valid till 031501)



The PDF file for the ADC is:
http://www.national.com/ds/AD/ADC0844.pdf

On page 16 of the document they have an example 8051 schematic, the only difference is that they tie the ADC chip select to one of the IO pins and I simply ground it. They have example code on the same page.

I've not looked carefully at the part nor the advantages of grounded CS compared to controlling it. I assume that you have no other part on the data bus.

It should be a fun project. I've played around with some National Semi ADCs and it was a lot of fun.

You might want to hook the device up to send samples to your PC over the serial link. We did something like this to evaluate some temperature and relative humidity sensors and with such a collection of sample points, you can tell when the office airconditioner kicked in over the weekend.

We just collected a data stream and displayed them into Excel spreadsheet and the characteristic pattern showed us that our office airconditioner was kicking in every 45 minutes during the daylight summer hours and you could easily see the duty cycle. The progression of airconditioning was also dehumidifying the air over the course of the day and you could even see the 45 minute cycle in it... it was quite interesting but useless data. :)

aka j