During the development of one light controller (more on this later) I had a requirement for two analog inputs that would allow connection of external LDRs to enable operation only in low light conditions. Normally you would just use a basic voltage divider with an LDR going to supply voltage and feed the output directly to an ADC. But since this particular LDR was supposed to be connected via long cable I wanted to have a robust analog input that would survive any transients and/or crazy connections that might occur during installation and normal operation.
This is not it. This is the basic circuit that will be used as a starting point: a voltage divider with a non-inverting unity gain amplifier as an input buffer. It works as a universal 0-5V analog input and can be easily expanded to 0-10V using a different value for resistor R2 (see notes below). Another advantage of R2 is that it provides a known reference when nothing is connected to the input so you can also detect broken wire conditions for resistive sensors.
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