Posted on May 17, 2011 at 14:33It's probably safe - but it's wrong. Why not use a series schottky diode or a transistor or FET buffer. Devices are available which include series and bias resistors if you are trying to keep it small.
In general, there's a risk that if you bias the protection diodes in the analogue section you will cause small inaccuracies in ALL the analog measurements in that section.
