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136  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.
137  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.

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.
138  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.
139  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.
140  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.
141  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.
142  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.

143  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.
144  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.

145  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.
146  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.
147  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.
148  Using Arduino / General Electronics / Re: Calculating inductance on: December 19, 2013, 02:51:25 am
Will the inductor have any DC flowing thru it?
If yes, then you also must consider the maximum DC current that the inductor can handle before it saturates.
149  Using Arduino / Sensors / Re: Wind Speed Sensor WH2080 on: December 17, 2013, 06:44:08 pm
Buying Wind Sensors by themselves to use in an application differant to what they were intended for is risky
for 2 reasons.
If its a wireless sensor as this one appears to be , then you will either have to dismantle the sensor to figure out
how the wind speed direction and speed are detected, or you will have to reverse engineer the radio protocol that the sensor uses.
Even if you can get this all working, you will have to figure out the relationship between the spin rate of the anemometer and the actual wind speed, and this is not easy to do.
Unless the Wind Sensor comes with a calibration chart which shows the relationship, then you will have to calibrate the wind sensor to get the wind speed correct.
Try and buy a wind sensor from a reputable supplier who will provide the calibration data if you want accuracy.

150  Using Arduino / Motors, Mechanics, and Power / Re: GSM Shield battery power supply? on: December 17, 2013, 04:45:05 pm
The voltage of a battery doesnt tell you how much electrical energy the battery holds, and although the little 9v batteries
are nominally 9 volts, their capacity is only around 100 - 200 mah, so they cant power very much.
Running a GSM shield where it transmits every 20 seconds will be very hard to run off a battery unless there is some mechanism for
charging the battery on a regular basis, or regularily replacing the battery.
Whats the application involved?

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