On 13/04/2018 18:47, The Natural Philosopher wrote:
On 13/04/18 17:24, newshound wrote:


As you say, small mains transformer, a few resistors and of course a
5 volt Zener on the ADC input.

Well i'd just clamp that to the 5V rails.

Clamp what? I'm confused.

The input.

resistor and reverse biased diode to +5V. If it goes above 5V the diode
clamps it to the suplly rail plus half a volt or so. Standsard technique.


https://i.stack.imgur.com/LfzyT.png

is a perfect example

from a similar app.

https://electronics.stackexchange.co...erence-voltage


OK perhaps I am getting my Zeners and Shottkys mixed up, it is a long
time since I actually built anything like that. But that's the principle
I was trying to convey.