hi,

I have ask this question due an your friends experience.

Looking on messages of the forum I have found a couple of messages where people indicate an idea to use analog inputs as multiple digital ones. For example, with each channel of SiLabs 10/12-bit ADC it is possible to control about 8 buttons (or even more). The idea is to use R2R network constructed from buttons and resistors which provides voltage level to ADC channel.
Now is the question: does someone have utilized such way? I have done an experiment and connot obtain good results. Well, analog schemaic is not my good side, but I tried only 4 buttons and have not obtained good and stable voltage. The problem I see is that I cannot use direct Vref from SiLabs F120 due its high-impedance output from one side, and Vcc due it is not stable value (relative) from other side. Global problem is that I have limited myself with no way of calibration.
I see a next way: I use OpAmp as voltage follower from Vref. Then I use DAC R2R from buttons and output voltage of the OpAmp. Result voltage I provide to input of chip ADC. When I use strong switch buttons then result is more or less good. But when I try to isolate buttons with optocouplers then I cannot obtain any appropriate results.
So, does anybody have real worked schematic of this task, could you public it here, please? I will pass a beer for you then (=
One more note: the question is from my argument with a colleague that this way is possible in the practice. Indeed, it may be useful for all 8051 users.

Thanks,
Oleg