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Mario Vernari

Member Since 22 Jan 2011
Offline Last Active May 05 2017 11:55 AM
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In Topic: How to interface and measure a capacitive sensor?

12 November 2015 - 07:56 AM

I never said the circuit is not working: I've said that's very critical. I mean that if you're going to create more-than-just-one circuit, you'll have to re-tune each one, because the inherent error, tolerance and whatever will lead to (even to) dramatic different results.

 

A typical resistor is given at 5%, but you might find at 1% as well. The capacitance of a comb plate is due to many factors: exposed surface area, dielectric, and distance. Thus, upon a temperature range of, let's say, 0 to 40°C, you'll have a very different C, despite the same rain fall.

 

Have a try, and you'll face the problem. However, if you're going to create a single one, okay, you can tune it perfectly, table its trans-characteristics on software and plot a real behavior upon rain and temperature.

 

I really didn't want to fire discussions: just to alert other readers that the problem isn't simple!

Cheers


In Topic: How to interface and measure a capacitive sensor?

10 November 2015 - 08:11 AM

Fine!

Just a word about the oscillator...

The frequency of that circuit is something like: f=K/(R*C), where K is a constant.

The relevant thing is that a capacitance-delta is behaving in a hyperbolic way to the frequency. That is, even a small fluctuation of the capacitance (or resistance) will actually produce a huge shift of the expected frequency.

You should avoid coupling high R with small C: leave the oscillator running fast and count how many pulses it feeds in some "capture" input. Any cheap *duino is able to count MHz without any problem.

 

We don't use Davis' products. Our rain detector is basically a water flow meter. However, that's *not* a product of our labs: we just use it.

Cheers


In Topic: How to interface and measure a capacitive sensor?

09 November 2015 - 08:27 AM

I don't think you'll get decent (i.e. accurate) results with a simple oscillator: the capacitance is pretty small and also spans along a short range. Moreover, as you correctly pointed out, the Netduino itself won't be able to capture a so high frequency, although I believe you'd have hard time to read it with an Arduino-like board.

Such a sensor is surely cheap but much reliable: it's just a comb-shaped pair of plates, which offers a different electrostatic behavior upon the quantity of water on it...

Water? how this water is composed? what if the rain is mixed with sand, since often we experience red-rains due the African desert wind?

 

I don't know if that might help you, but we faced the generic "weather" station a while ago, for real cases, not just hobby/home purposes. We've a complete set of sensors for accurate telemetry, even without TCP/IP layer and for pretty long distances (up to some km).

Have a look  here, just for your information...

http://www.cet-elect...ti/sensors.html

 

Cheers


In Topic: LCD-Boost library for Netduino

20 October 2015 - 12:00 PM

Sorry for being in late.

The boost library leverages its performance by a hardware trick: you must use it, otherwise the library not only won't help you, but even won't work at all.

The Stefan's library is more intuitive and maybe more straightforward to wire, but you can't get it faster because the interpreted framework. That's because I used a hardware solution as a workaround.

 

From your photo I realize that you already finalized the hardware. I believe there's no clues for pushing the speed greater...

Cheers


In Topic: Gameduino 2 For Netduino

31 July 2015 - 05:47 AM

Were you able to display images?

I stopped my porting because of that...


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