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136  Using Arduino / Project Guidance / Re: dual axis solar tracker for mobile/portable installation of solar panels on: January 28, 2014, 07:36:13 am
The fundamental problem with small wind turbines, which are the type that might be used in camping or erected on a short pole
is the swept area is simply too small to gather any usuable wind , unless the wind speeds are 40 kmh + .
As the power in wind is proportional to the cube of the wind speed, small drops in the wind mean really large drops in output power.
A good example is a popular small wind turbine called an Air X 400, which is a small 400 watt turbine with a rotor diameter of 1.5 Metres.
To get 400 watts , you need a wind speed of 45 kmh, and because of the cubed law, at half the speed you get 50 watts.
Ok if you live somewhere near the coast where the wind is always blowing a gale.
Then there is the cost, and small wind turbines are very expensive relative to the power they make.
You are much better off with Solar panels for the same cost.

137  Using Arduino / Project Guidance / Re: dual axis solar tracker for mobile/portable installation of solar panels on: January 27, 2014, 06:29:46 pm
Before you even think about any kind of vertical axis wind turbine , make sure you examine closely the
power output versus wind speed for the turbine you are considering.
All VAWTs fall into 2 categories.
They are either a Savonious rotor design, which are fairly common , but extremely inefficient as they are a drag rotor and need
hi wind speeds to make any usuable amount of power.
The other type is a Darrieus vane which do work well, but are extremely large and need very substantial mounting structures, so are not viable for most people.
138  Using Arduino / Project Guidance / Re: dual axis solar tracker for mobile/portable installation of solar panels on: January 26, 2014, 02:08:23 am
Why do you want to do this?
Have you looked at the economics of how much extra power you would get from a tracked array
and the economics of simply having a fixed array with an extra solar panel added.
Its generally easier and cheaper to add extra panels than to make a tracking array for a smaller number.
139  Using Arduino / Networking, Protocols, and Devices / Re: 433.92 Mhz garage gate opener on: January 25, 2014, 02:35:09 am
Very hard to help here, as more information is needed.
Just having a transmitter on 433.92 Mhz isnt enough, as the type of receiver in the garage gate is needed.
Garage door openers frequently use rolling code transmitters for security, and if this is the case, then simply
recording the transmission wont help, as it changes every time you open the door.
If you can read the IC type in the transmitter , it may help determine what type it is.
140  Using Arduino / General Electronics / Re: how to calculate the exact frequency of this FM transmitter? on: January 17, 2014, 05:17:57 pm
Get yourself a copy of this book.
http://www.arrl.org/arrl-handbook-2014

It explains the basic theory of Radio Comm pretty well, and has constructional articles of how to build both transmitterss and receivers.
Dont expect to learn everything in 5 minutes though.
141  Using Arduino / General Electronics / Re: how to calculate the exact frequency of this FM transmitter? on: January 17, 2014, 01:38:35 am
I think the OP may be a bit confused re what is needed.
A few posts back, the OP indicated they wanted to make a walkie talkie.
Firstly, such radios dont operate in the FM band, but usually in the 433 - 434 UHF band , similar to UHF CB radios.
Such radios use narrow band FM , bandwidth limited to a 10 Khz channel, with typically 5 Khz deviation.
In this case its essential that the frequency stability of the both the transmitter and receiver is controlled by a crystal oscillator
which usually provides the clock for a fractional N dual modulus pre scaling synthesiser.
In my work life I used to design and make such things, and its not that hard to do , but sure isnt a beginners project.
Heres a bit of an article on how such devices work.
Its a bit old , and there are far better ICs around now , but the explanation is easy to understand.
http://epic.mcmaster.ca/~elmer101/wx_synth/wx_pll.htm
142  Using Arduino / General Electronics / Re: how to calculate the exact frequency of this FM transmitter? on: January 16, 2014, 07:00:32 am
What are you trying to do with this transmitter?
The frequency is given by the formula 1 / 2 X pi X sqroot (L X C), but as
the circuit has the oscillator as the output stage , its frequency stability will be terrible.
You need some kind of crystal oscillator followed by a multiplier to get a stable frequency.
143  Using Arduino / Networking, Protocols, and Devices / Re: Super simple wireless on: January 14, 2014, 05:43:47 pm
Its unclear whether you want bi directional transmission capability or not , but if so you need radio modules
that are bi directional and that limits you to Xbees or the NRF series of modules.
If uni directional transmission is OK, then you can use the much cheaper and simpler 433.92 Mhz ASK modules.
Most remote light switches are uni directional.
144  Using Arduino / Networking, Protocols, and Devices / Re: Max amount of slaves in a wireless system? on: January 08, 2014, 10:43:59 pm
From a practical perspective, it depends on what the slaves are required to send and how often.
Since the entire system is sharing a common frequency, you can basically determine the number of slaves by simply dividing the
data requirement of each slave into the total bandwidth available.
145  Using Arduino / Project Guidance / Re: ringing phone on: January 06, 2014, 09:45:01 pm
The bell itself only needs AC at around 90V
The referance to 48V DC was that phones traditionally were fed from a 48 V battery in the telephone exchange so there was
always 48 V on the line when the phone was on the hook.
To make the bell ring, 90 V AC was superimposed on the 48 V DC, but the bell only got to see the AC as they had capacitors in series with them.
Depending on how loudly you want the bell to ring, you could try much lower voltages than the 90 V.
You will however need some way of generating the low frequency AC voltage for the bell.
A simpler solution would be to junk the bell altogether and use a low voltage DC buzzer which an Arduino can easily drive
with a simple transistor switch.

146  Using Arduino / Networking, Protocols, and Devices / Re: 433 mhz RF Servo control Potentiometer value on: January 05, 2014, 04:04:04 pm
You need a full duplex radio link to do this , as you need feedback from the servo as to what its position is .
You can do this with the NRF type radio modules as they are bi directional, but the 433 Mhz modules are not.
147  Using Arduino / Project Guidance / Re: Detect interference from power lines on: January 02, 2014, 05:53:08 pm
What kind of interferance is causing the RC planes to be lost?
The 2.4 Ghz band is in most countries part of the ISM band, which stands for Industrial, Scientific and Medical band.
There are many devices capable of causing wide scale interferance in this band , but power lines is not likley to be one of them.

148  Using Arduino / Project Guidance / Re: Detect interference from power lines on: January 02, 2014, 04:26:41 pm
110KV transformers you will only find in zone sub stations .
You wont find them anywhere along  the power line.
To measure interferance at 2.4 Ghz , you need a receiver that is designed for operation at this frequency.
This means an antenna designed for 2.4 Ghz and a receiver with a RF amplifier also designed for 2.4 Ghz.
Id be very surprised if you measure anything at 2.4 Ghz from a power line as theres no obvious mechanism to create it.
149  Using Arduino / General Electronics / Re: Morse Code Tx and Rx on: December 27, 2013, 06:40:54 am
Decoding morse code is hard to do, unless its generated by a machine which maintains constant timing.
ie the length of the dots and dashes dont change.
If its being sent by hand, you will have a very hard task decoding it.
150  Topics / Home Automation and Networked Objects / Re: light switch rf control on: December 26, 2013, 05:29:53 pm
The rc switch library relies on the remote being controlled having a Sc2272 or similar decoder chip inside it.
Whilst this chip is pretty common, its not universal.
You may have to pull the remote switch apart to see what it uses.
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