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181  Using Arduino / Project Guidance / Re: Transfer of charge wirelessly via inductive coupling on: November 02, 2013, 12:34:28 am
What is your goal here?
How much power do you want to transfer?
What will be connected to the secondary coil.
Your questions are too vague to really comment on.
182  Using Arduino / General Electronics / Re: cell phone jammer using house Mains ground as antenna on: October 29, 2013, 08:21:17 pm
To answer the original question the answer is no .
To make any kind of antenna that is in any way efficient , the antenna has to be resonant with respect to the frequency of the
energy being fed into it.
Most Cell phones operate on frequencies from 800 Mhz upwards.
Theres no way of connecting a transmitter on these types of frequencies to any kind of random length long wire antenna and expecting the wire to radiate the energy.
183  Using Arduino / General Electronics / Re: Easiest way to monitor a small solar panel on: October 29, 2013, 08:15:14 pm
What precisely are you trying to measure?
The output power of a solar panel varies depending on a large number of variables.
Primarily the solar radiation intensity , which changes over the course of the day, and whatever the solar panel is connected too.
Fixed value resistors will provide some data , but it wont mean much , as the values have to be changed depending on the level of light intensity.
To accurately measure how much power the solar panel can deliver over a period of time , needs a MPPT (Maximum Peak Power Tracker) which is an electronic device that continuously adjusts the apparent load to match the solar panels peak power point , and a battery to absorb the energy.
You could use a resistor instead of the battery if you dont care what happens to the Solar panels output.
You can make a MPPT charger with an Arduino if you wish.
Heres an article on how to do so.
http://www.timnolan.com/?page=arduino-ppt-solar-charger
184  Using Arduino / General Electronics / Re: How does Radio control of RC cars works without any antennas and using a LED? on: October 26, 2013, 02:10:37 am
IR generally works for indoor control, and they will work outdoor at night,or on very cloudy days  when theres no sun.
Sunlight totally swamps the receivers and they dont work.
Range is pretty limited.
185  Using Arduino / Sensors / Re: I am having trouble with a DHT22 temperature sensor to work on Arduino Mini Pro on: October 20, 2013, 07:08:08 pm
You need a pullup resistor of between around 3.3K and 10K on the sensor data line.
Without one , it might work , but will be very unreliable.
186  Using Arduino / Project Guidance / Re: Solar Powered Water Pump with Back up Battery on: October 20, 2013, 12:36:50 am
The energy needed to pump water is determined by the flow rate , ie how many litres per minute , and the head, ie
how far vertically the water has to be pumped.
Unless these values are known , its impossible to determine how much power you will have to generate with the Solar Panel.
187  Using Arduino / Networking, Protocols, and Devices / Re: Questions about WLANS, Wireless Networks, and Wifi on: October 18, 2013, 05:40:40 pm
OFDM is a technique used by services like digital TV transmitters and also digital radio to transmit
hi bit rate data is a bandwidth limited channel.
Transmitting hi bit rate data is hard, as it gets affected by transmission anomalies like frequency selective fading
and multipath.
To overcome these problems , OFDM was developed which transmits hi bit rate data at a slow bit rate, which might sound impossible.
To do this , the hi bit rate data is broken down into lots of low bit rate channels, which are all stacked next to each other and the whole lot is transmitted together.
At the receiving end , all the low bit rate channels are demultiplexed and the original hi bit rate data is reconstructed.
This makes the transmission quite rugged , and impervious to frequency selective fading and multipath.
188  Using Arduino / Networking, Protocols, and Devices / Re: Questions about WLANS, Wireless Networks, and Wifi on: October 14, 2013, 02:52:11 am
Its a frequency stability problem.
At 2.4 Ghz , to maintain a 1 Khz channel , needs a frequency stability of 4 in 10^7, which whilst possible needs
extremely good oscillators.
Theres also little need for 1 Khz wide channels at 2.4 Ghz .
Generally, the higher frequencies are chosen ,so that faster bit rates can be achieved.
How fast depends on many variables, but the theoretical limit is set by the bandwidth and the signal to noise ratio.
http://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theorem
Shannons theorem, as its commonly called, explains the relationship between maximum data rate, channel bandwidth
and signal to noise ratio for communication over a noise limited communications channel.


189  Using Arduino / Project Guidance / Re: Outdoor & Indoor remote weather/temp system on: October 13, 2013, 04:41:39 pm
Its easy to build a temperature / humidity sensor , but a lot harder to build a rain guage.
Ive built a number of temperature / humidity sensors using the DHT22 , a small micro and a 433 Mhz transmitter.
Some issues you need to think about is do you want to expand the system later and add more sensors.
190  Using Arduino / Motors, Mechanics, and Power / Re: Using LiPo Fuel Gauge for reading THIS! battery pack on: October 12, 2013, 03:58:16 am
Dont confuse precision with resolution.
The Arduino can read to a resolution of 4.9 mv , but that doesnt mean its accurate to 4.9 mv.
Its accuracy is set by the accuracy of whatever its using as its voltage referance.
191  Using Arduino / Project Guidance / Re: Energy monitor on: October 12, 2013, 03:50:11 am
How big are the batteries and how are they wired. (series or parallel).
A 1100 watt Inverter can pull close to 100 amps from a 12V battery and this will rapidly deplete the battery.
You need some idea of how much energy is going to be consumed each day.
192  Using Arduino / Project Guidance / Re: Radio direction finder on: October 11, 2013, 01:14:15 am
The voltage by itself isnt enough to get direction.
You also need to measure the phase angle between the 2 RF signals from each antenna to get the quadrant info.
193  Using Arduino / Networking, Protocols, and Devices / Re: Arduino RF communication problem on: October 10, 2013, 05:56:29 pm
Why dont you want to use Sc2262 Sc2272 devices.
They will do exactly what you want.
194  Using Arduino / Project Guidance / Re: Best Arduino wireless communication solution - 350Mhz / 433Mhz / 950Mhz / 2.4Ghz on: October 10, 2013, 12:17:17 am
What do you mean by module?
Are you just talking about Transmitters, or Transmitters and Receivers.
The power consumption of them all is totally dependant on how much of the time they are transmitting.
The receivers need to be running all the time , and they are relatively power hungry.
Basically, the bottom line is the power consumption is proportional to the range you need.
Do you need full duplex or half duplex transmission.
Do you need inbuilt error correction.
Without any understanding of your needs , its impossible to answer.
195  Using Arduino / General Electronics / Re: how do 2.4 Ghz transmitters work on: October 03, 2013, 01:10:31 am
Not sure I fully understand your question, but this is how the 2.4 Ghz frequency is generated.
 The 2.4 Ghz transmitter frequency is generated by a voltage controlled oscillator which feeds
a very hi frequency divider called a dual modulus prescaler.
This chip divides the 2.4 Ghz signal down to a much lower value where its compared with a similar value from a conventional crystal oscillator using a phase detector.
The phase detector produces a variable output DC voltage which controls the frequency of the 2.4 Ghz oscillator.
This gives a stable frequency at 2.4 Ghz which equals the stability of the crystal oscillator used to do the comparison.
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