user-1: I need to connect a speed sensor module with an Arduino Due and calculate the speed of an approaching object.
the sensor is:
http://www.limpkin.fr/index.php?post/2013/08/09/Making-the-electronics-for-a-%247-USD-doppler-motion-sensor
The sensor already output a signal that its' frequency represents the speed of the object.
I would really appreciate any help understating how can it be connected and operated by the Arduino without burning it, and how can I sample its output?
If more details are needed I'll be happy to supply.
Thanks.

user3720: The articles and tutorials I've read on the subject say that the HB100 module produces a very weak signal which needs to be amplified before your Arduino can read it. They recommend building an op amp. This post on the Arduino forums, for example: http://forum.arduino.cc/index.php?topic=61989.0
BUT looking at your picture and linked article, I find that your device already includes the signal amplification and filtering you need in the backpack board. I found the store page for this module, which has a more noob-friendly explanation. From what I gather:

VCC: provide the module with a 5v supply.
VOUT: analog reading of the amount of return signal being received. My guess is you could use this with analogRead() to get a rough estimate of the size or distance of the object being read. If you want only the speed reading, you don't need this pin.
FOUT: digital output of the speed that the sensor is reading. Thanks to @sachleen's link, you can use either pulseIn() or FreqCounter library to measure the frequency and then convert it to a MPH or KPH speed.
GND - ground, aka common, aka -.

So connect VCC to 5v, GND to ground, and FOUT to an input pin on your Arduino. If you use pulseIn(), frequency f = 1 / t, t being the return value from pulseIn(). If you use the FreqCounter library, it no doubt has documentation on its usage.

-1: <p>I need to connect a speed sensor module with an Arduino Due and calculate the speed of an approaching object.</p>

<p>the sensor is:
<a href="http://www.limpkin.fr/index.php?post/2013/08/09/Making-the-electronics-for-a-%247-USD-doppler-motion-sensor" rel="nofollow noreferrer">http://www.limpkin.fr/index.php?post/2013/08/09/Making-the-electronics-for-a-%247-USD-doppler-motion-sensor</a></p>

<p>The sensor already output a signal that its' frequency represents the speed of the object.</p>

<p>I would really appreciate any help understating how can it be connected and operated by the Arduino without burning it, and how can I sample its output?</p>

<p>If more details are needed I'll be happy to supply.</p>

<p>Thanks.<img src="https://i.stack.imgur.com/bCYgd.jpg" alt="The module&#39;s connectors"></p>
 3720: <p>The articles and tutorials I've read on the subject say that the HB100 module produces a very weak signal which needs to be amplified before your Arduino can read it. They recommend building an op amp. This post on the Arduino forums, for example: <a href="http://forum.arduino.cc/index.php?topic=61989.0" rel="nofollow">http://forum.arduino.cc/index.php?topic=61989.0</a></p>

<p>BUT looking at your picture and linked article, I find that your device already includes the signal amplification and filtering you need in the backpack board. I found the <a href="https://www.tindie.com/products/limpkin/hb100-doppler-module-with-backpack-1/" rel="nofollow">store page</a> for this module, which has a more noob-friendly explanation. From what I gather:</p>

<ul>
<li>VCC: provide the module with a 5v supply.</li>
<li>VOUT: analog reading of the <em>amount</em> of return signal being received. My guess is you could use this with <code>analogRead()</code> to get a rough estimate of the size or distance of the object being read. If you want only the speed reading, you don't need this pin.</li>
<li>FOUT: digital output of the speed that the sensor is reading. Thanks to @sachleen's <a href="https://tushev.org/articles/arduino/9/measuring-frequency-with-arduino" rel="nofollow">link</a>, you can use either <code>pulseIn()</code> or FreqCounter library to measure the frequency and then convert it to a MPH or KPH speed.</li>
<li>GND - ground, aka common, aka <code>-</code>.</li>
</ul>

<p>So connect VCC to 5v, GND to ground, and FOUT to an input pin on your Arduino. If you use <code>pulseIn()</code>, frequency <strong>f</strong> = 1 / <strong>t</strong>, t being the return value from <code>pulseIn()</code>. If you use the FreqCounter library, it no doubt has documentation on its usage.</p>
