Hello!

I'm currently implementing a dual slope ADC (TL501C from TI).
It consists of two control lines, A and B.
00 = Autozero (reset and storage of offset voltage on an offset cap.)
11 = Integrate Vmeas (integrating the measured voltage 0-5V under a specified time = T1)
10 = Integrate Vref (integrating Reference Voltage 2.5V)

When Vref integration is finnished, an interrupt (INT1) is provoked. I'm measuring the time and setting the control lines via the timer 0 interrupt. The INT1 is high priority above the timer 0 and is only enabled when needed (When AB=10).

The formula for the Measured voltage is: Vin/Vref = -T2/T1

I have played around for a while now, but I can't get a linear measuring when voltage is measured within the 0-5V area.

I will therefore share the problem with you. I'm sure some of you may have some experience with the use of a dual slope converter. The advantage of the dual slope is that the offset values are not important, and the times T1, T2 abs. values is not important, only thier ratios.

If anyone need more information of the ADC I can pass the Datasheet to you, but it don't describes the ADC very well. I had to write an e-mail to Texas Instruments to get it.
For other information, I'm using a AT89C51 controller.

Best regards
John E. Finnekaasa