8 replies to this topic

[denisj]

Hi there all and congratulations for the forum and the netduino invent :-) I just want to begin a home progect and i want to monitor some consumers aroud my home. For first thinks if anyone can help me i'm looking all net to find a non invasive current reader that allready have a zigbee trnsmiter (and maybe that function using the battery) Then i want to buy the netduino plus (in europe) with the zigbee interface, in order to read all data that the current sensor send me. Is there anybody that allready make this ...or have allready see some zigbee sensor for current please ? Thanks in advance. Denis

[Dan Morphis]

Hi there all
and congratulations for the forum and the netduino invent :-)

I just want to begin a home progect and i want to monitor
some consumers aroud my home.

For first thinks if anyone can help me
i'm looking all net to find a non invasive current reader that allready have a zigbee
trnsmiter (and maybe that function using the battery)

Then i want to buy the netduino plus (in europe) with the zigbee interface,
in order to read all data that the current sensor send me.

Is there anybody that allready make this
...or have allready see some zigbee sensor for current please ?

Thanks in advance.
Denis

SparkFun has clamp-on current meter for $9.95 (US) that would work for your purposes. I don't think you'll find one with a ZigBee interface though.

[Michel Trahan]

We should have our netduino version of this project

[Mario Vernari]

I agree that it would be nice having something similar for our world, but... The Arduino project makes use of fast ADC readings to calculate the various units (i.e. voltage, current, power, etc): that is not possible with Netduino. It could be solved with additional analog circuitry (e.g. filtering, amplifiers, etc). Probably the current clamp is the simpler way to test a load, but it results a not reliable way to do it. The AC is described by vectors, so complex math, and it needs both amplitude and phase. If you consider a pure-resistive load (e.g. an iron), then the current measured by the coil would give the correct value, because voltage and current are perfectly "in-phase". That is 230V x 1A = 230W. But if you consider an inductive load (e.g. a free-running motor), then voltage and current would have a certain phase-angle. That angle should be taken in account because it is *NOT* what your electric company measures. Theoretically speaking: 230V x 1A (90' degree) = 230 VAR, but 0W!!! You won't pay any VAR, but only Watts instead. The best way to measure a load is having two little transformers: one in series for the current and the other in parallel for the voltage. The MCU should sample both the transformers and apply the vectors math to calculate the most common readings. Cheers

[denisj]

Deal all, thanks for the answers. I just still looking for some harware around i found a lot of sites (http://www.currentco...ransmitter.html) that use the reader for commercial scope. But i still can't find a reader to buy for use it alone for my project. Mario... nice to meet you, I live near Milan (Casarile). The true is that i did't care what i must use for the current reader sensor But important is that i can use the .Net programation lang to monitor it cause i think is more easy than the C lang. I wish to have 2 readers (one for the general home power and another for my photovoltaic system) and monitor it on the netduino... have the diference on some android pad that access to netduino ... i hope :-) So do you think is possible to use a reader sensor with inside arduino and than use a netduino to monitor it ? sorry ... what is "fast ADC" please ? I just take a look on your blog :-) Thanks again all Denis

[Mario Vernari]

Well to know that you are living in my same country! I think that a simple clamp would be sufficient, at least until you don't care about precision, phase, etc. A clamp is basically a coil with a resistor. The alternating current flowing through the tested cable induces a current (electromagnetically) to the coil. That current flowing in the resistor produces a voltage, also sinusoidal: your goal is to measure that voltage. The main problem is that it is small (hundreds of millivolts) and it is sinusoidal. That usually solves using rectifiers and amplifiers. Another way is using a controller with an ADC. The CPU reads the voltage by the ADC, at least as fast as enough to fit the whole sine. Treating of 50Hz (for EU), you should sample the signal *at least* every 1/(2*f), that is 10ms. The truth is better to oversample as little as 1ms, for example. This trick allows you to make less computation, because the sine shape is reconstructed better (interpolation). An Arduino-like board works using native code and it is very fast, so it won't be a problem to sample even under one millisecond. By contrast, using Netduino, you will have tons of powerful libraries (.Net Micro Framework), that simplify your life on relatively large projects. The best way I'd suggest, is using a Netduino board with a small circuit as input: an amplifier and rectifier. That is NOT simple if you haven't some basis on electronics, but it looks to me as a very flexible way to create what you mean. A simple question: is your project a single sample or it should be produced in relative quantity? Another question: does it require a good reliability or not? Ciao

[denisj]

Here i found on http://smartenergykit.com/explore/ a clip that can send every second via zigbee and a wonderfool think... it's power by itself using the current induction I think is the best point :-) Denis

[Mario Vernari]

Ciao Denis! I don't forget your problem, and just today morning I have promised to write a small tutorial on how to create a simple power meter. I think I could be able to write it during the next weekend.

[mpearson]

Another option is one of these Current Transformers from Dig-Key.

If you use the Spark Fun or Digi-Key version, you will need to rectify (AC to DC), and condition the signal. Here is an App note on this. I will be using one of these in my projects. A possible solution for someone that is interested in learning more about electronics.

My inclination is more on the hardware side, but I am very interested in learning the .net framework.

Take care,
Mike