Hi,

sorry, the circuit cannot be read. OTOH, you can try digital potentiometer
from Xicor or from DALLAS...

I hope this helps.

Imre


On Tue, 26 Oct 1999, Nikolai Golovchenko wrote:

> Hello all.
> I need to read 50Hz signal with PIC16F877. Actually, 10-bit accuracy is
> enough, but the signal level is unknown, therefore PIC has to adjust to the
> signal. The level changes relatively slowly and there is some time allowed
> for adjusting. In this case four gain bands (1:2, 1:4, 1:8, 1:16) will do
> the job.
>
> Now, the problem is that I don't want to use variable gain amps, because
> they are too expensive and hard to get here, in Ukraine. Another way is to
> use analog switches which will change the gain of a usual op amp. Can the
> PIC's pins be used as analog switches, connected to ground? The datasheet
> says that ports use FETS and that the leakage current is as small sa 1uA.
>
> I would connect four resistors to PIC and made the pins go low or tri-state.
> Will the circuit work?
>
>          __
> -------| + \
>          |       \
>          |         >------------- To RA0/AN0
>          |        /          |
>      ---|--  /              |
>      |        ____      |
>      |-----[_____]----
> ---------
> ---------
>      |----------------
>      |      |      |     |
>     [ ]    [ ]   [ ]   [ ]
>     [ ]    [ ]   [ ]   [ ]
>      |      |      |     |
>      |      |      |     ----------    RA1
>      |      |      ---------------    RA2
>      |      ---------------------   RA3
>      --------------------------    RA5
>
> Thanks in advance.
>
>