I have a sensor (NRG #40 Anemometer) that produces an AC signal with a frequency between 2 Hz to ~100 Hz with an amplitude of 80 mV to 12 V peak-to-peak. The signal to read is the frequency (zero crossing?), amplitude is not relevant.
The signal gets read by a Arduino Uno. To convert the sine wave (from the sensor) to a square wave (suitable for the MCU input), I was thinking of using a 74HC14N Hex inverting Schmitt trigger. The sensor application note suggests adding Over-Voltage Protection, Low-Pass Filter and a limiter. I am running the Schmitt trigger at 3.3V.
Unfortunately my Schmitt Trigger output is always high, meaning the input signal is low and doesn't register.
- How can I bring the input signal to a valid level for the Schmitt trigger?
- How can I DC bias the input signal to about 1.65 V and limit it to not pass 3.3 V and 0 V?
- I thought I ignore the Over-Voltage Protection and Low-Pass Filter for the test setup, is this ok?