I am hoping to interface an NRG #40C anemometer to an Arduino. The anemometer outputs a frequency which is linear with the wind speed which equates to 1.711 mph/Hz. However the output voltage ranges from 80mV p-t-p to approximately 12V p-t-p at 60Hz, which approximates to a wind speed of 100mph. The manufacturer states that the voltage is non-linear with wind speed, so as the wind speed increases so do both the frequency and amplitude, but only the frequency is a linear increase.

I have no design experience but I am quite competent at the construction of projects. I am hoping that someone has, or able to design, a suitable circuit that will convert the variable amplitude sine wave into a square wave suitable to be fed to a digital input pin on an Arduino and then convert the frequency to the wind speed. The software side of this is quite easy

An alternative would be a frequency to voltage converter, but I am still concerned regarding what I see as a massive range of input voltages.

  • \$\begingroup\$ does the frequency or the amplitude change with the windspeed? \$\endgroup\$ – Wesley Lee Nov 29 '15 at 21:40
  • \$\begingroup\$ You can use back-to-back zener diodes to limit the voltage. Use current limiting resistors at the anemometer output to avoid putting too much load on the anemometer. Run the signal to a comparator first, then to the Arduino. Unless the Arduino has a comparator input, in which case you can use that. I can draw a schematic if you want. Or you can take a stab at it yourself if you have a rough idea what I mean. \$\endgroup\$ – mkeith Nov 29 '15 at 22:28
  • \$\begingroup\$ So, what is your question? \$\endgroup\$ – Andy aka Nov 29 '15 at 23:02
  • \$\begingroup\$ Have you considered a square wave output (reed switch) anemometer like the Comptus A75-101? \$\endgroup\$ – user110252 May 16 '16 at 13:10

Sounds like a comparator would be a good option. AC couple the signal from the anemometer into a comparator. Add a large voltage divider after the cap to get a good reference level. Make sure the voltage divider and cap will give you a show enough timestamp - you may need to use a rather large capacitor. Then use a comparator circuit that has a few 10s of mv of hysteresis. Place a couple of diodes between the comparator input and the voltage for protection.

  • \$\begingroup\$ A Schmitt trigger may also do the trick. \$\endgroup\$ – Wossname Sep 28 '16 at 9:00

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