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181  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.
182  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.
183  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.
184  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.
185  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.
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.

186  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.
187  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.
188  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.
189  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.
190  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.
191  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.
192  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.
193  Using Arduino / Project Guidance / Re: Replicating an RF remote signal on: September 30, 2013, 11:00:49 pm
Its important to not confuse learning remotes that work with IR , with those that work with RF.
Its dead easy to learn what the output of an IR transmitter is simply because the only transmission you will see
coming from the IR receiver is your own.
With RF, there will be stuff coming from the receiver all the time, even when you arnt transmitting,so the receiving code
needs to be able to sort out the garbage from the wanted data.
194  Using Arduino / Networking, Protocols, and Devices / Re: 433MHz Simple RF Link Kit on: September 30, 2013, 05:30:24 am
No, the Virtual Wire library uses Manchester Coding which has inherant error detection in it .
You either get the correct result or in this case, you wont get any data output.
And thats the other issue, if both transmitters transmit at once , neither transmission will be received.
If its necessary to have to separate radio channels in close proximity, then you need 2 separate radio channels
which could be done by using both 433 and 315 Mhz radios.
195  Using Arduino / General Electronics / Re: Ambient radio wave energy on: September 30, 2013, 05:03:44 am
This is difficult to do.
Whilst there is a lot of radio frequency energy being transmitted from multiple radio transmitters all around
its simply not possible to somehow add it all together and generate any power.
This is because its all AC and the phase relationships of all the transmissions are not related to each other in any way.
This simplest way and the most likley is the humble MF crystal set, consisting of a simple tuned circuit to isolate a single
transmission, a diode to rectify it , and a capacitor to charge.
But dont expect to get much energy, unless you live across the road from a 50+KW transmitter.
The longer the antenna the better, and long wire antennas work well with MF broadcasting stations.
The single largest source of radio noise is the Sun, but its totally useless as its non coherant so the energy is spread
across a wide bandwidth.
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