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166  Using Arduino / Sensors / Re: Deriving True Power with ACS712 on: December 16, 2013, 01:42:13 am
What are you intending to power with this set up?
Determining RMS volts is easy, but RMS amps is difficult if the load has any kind of active devices in the
power supply , like switch mode regulators, as the current waveform then is not sinusoidal.
You then need a true RMS converter to get the correct result.
Something like this.
167  Using Arduino / General Electronics / Re: Circuit Design Help? rectifier-voltage peak detector. on: December 14, 2013, 08:31:19 pm
The basic theory behind Joule Thief converters, requires a minimum voltage of approx 0.5V to get them to oscillate.
They use a single transistor as a self oscillating converter and with only 85 mv for input  , its extremely difficult to make a DC - Dc converter that will work.
168  Using Arduino / Project Guidance / Re: Decoding RF help on: December 13, 2013, 07:46:15 pm
That Nexa article does suggest its using some variant of the Sc2262 encoder, so all is not lost.
It will help you understand  whats being sent, but you will still have to figure out what the data being sent actually does.
A CRO is very useful for figuring this sort of stuff out.
Heres the datasheet for a SC2262 Encoder.

The data encoding format is described about 1/2 way in the article.
You may be able to spot the data patterns in your transmission.
Note, there is no timing standard as to how long the short bit or the long bit is , as both are set by a RC oscillator on the chip which can be changed by the user.
Note that the encoder is a trinary encoder, in that it can send 3 states, 0 , 1 and floating.
Quite often though the floating state is not used.

169  Using Arduino / Project Guidance / Re: Decoding RF help on: December 13, 2013, 04:47:07 pm
Decoding RF signals requires some knowledge of what is being used to generate the signal in the first place.
You need to know what type of data coding is being used, but Manchester coding is fairly common, but there are others.
In this type of coding , 1s and 0s are transmitted as positive to negative , or negative to positive transitions, which means the
data is self clocking and has no DC component.
Whilst not universal, a common approach is send a sequence of flag bits , which usually are represented as a sequence of 10101010 data pulses which last for 10 - 20 ms , followed by a unique and constant sync byte or nibble, which will be in some way always differant and easy to detect than the flag bits.
The purpose of the flag bits is to provide time for the receivers AGC loop to adjust to the incoming level of the RF signal
and the 1010101010 transitions allow the receivers data slicer to adjust to the 50% point of the incoming data.
Many common transmitters use one of the family of SC2262 / SC 2272 encoder , decoder chips , so if you can determine whether your transmitting device has one of these, then it makes the process a lot easier, otherwise you will have a difficult task.
The SC2262 encoder sends data as a sequence of short pulses or long pulses, with the data being conveyed by the pulse length.
Usually a logic 1 is a short pulse followed by a long pulse, a logic 0 is the reverse, ie a long pulse followed by a short.

170  Using Arduino / General Electronics / Re: Double RC circuit on: December 11, 2013, 05:50:15 pm
Simplest way to understand whats going on is to measure the leakage current of the capacitors.
I presume they are both electrolytics.
171  Topics / Device Hacking / Re: Opinions on intercepting 433MHz from Oregon Scientific WMR200 Weather Station on: December 10, 2013, 07:58:24 pm
You can cut the costs of OS sensors down by buying them directly from the US.
The prices in Australia are extremely high compared to the US prices.
I use a company called Price USA to do this , as OS in the US wont ship to Australia..
Ive managed to build a clone of a THGR810 temp / Hum sensor which does get decoded Ok on my OS weather stations
and also by a weather shield Arduino based decoder.
Ive got a WMR100 & a WMR80, but its not Arduino based.
Made it long before I learnt about Arduinos.
Its based on a Microchip 16F88 and is written in basic , not C .
Ill eventually get around to a C version.
OS do some funny things to the data that their Sensors transmit, to make it hard for people to make the sensors.
Guess they want to protect their product.
172  Topics / Device Hacking / Re: Opinions on intercepting 433MHz from Oregon Scientific WMR200 Weather Station on: December 10, 2013, 04:51:31 pm
Depends a lot on what you are trying to do.
Its easy to decode the data thats transmitted from Oregon sensors so that you can receive them using an Arduino and then display them on a PC which is connected to the Arduino.
Have a look here.
The weather shield is an Arduino based program that can decode the WMR100, 200 series of sensors.

If however , you want to make your own sensors and have them displayed on a Oregon console , then thats a lot harder to do
as there is information in the data that is sent from genuine OS stations that is not fully understood as to its function.
Ive built 2 Arduino weather shield decoders and they work fine .
Ive also made some of my own sensors, mainly temp / humidity ones and they also work fine when used with the Weather shield.
173  Using Arduino / Project Guidance / Re: Another smoking Leonardo on: December 08, 2013, 05:00:10 pm
Many Walwarts are unregulated power supplies which return a rated voltage when plugged into the device they were intended for
so a walwart rated at 12V which is designed for a modem / router will produce 12V when powering the router.
Routers draw far more current that a Arduino does, so using such a power supply on a Arduiono or Leonardo will result in more than 12V being delivered.
The Leonardo is rated at 12V max , and thats the board itself, not including any extra devices plugged in , such as LCD displays etc.
If the LCD display has a backlight, then theres a good chance the on board regulator is fried.

174  Using Arduino / Networking, Protocols, and Devices / Re: 433 Mhz RF signal cloning on: December 04, 2013, 06:34:31 pm
The RCswitch library relies on the encoder using a particular type of chipset which are listed here.
You will need to pull the key fob apart and see what the encoder chip is.
If its not one of the SC2272 type encoders, then using that library wont work.
175  Using Arduino / Sensors / Re: Capacitive Touch Piano on: December 04, 2013, 01:35:28 am
I cant see any sensing plates in your diagram.
The capsense library relies on a fairly large area of sensing plate to work properly.
If the plate is too small, the capacitance change becomes too small to detect.
176  Using Arduino / Networking, Protocols, and Devices / Re: testing 433 MHz reciever on: December 03, 2013, 11:12:17 pm
Yes, thats the most common method of using them.
The virtualwire library does all the hard work , so that the connection looks like a hardwired connection.
177  Using Arduino / General Electronics / Re: Can an AC Power inverter successfully power an arduino PWM load? on: December 03, 2013, 04:41:12 am
Zero cycle switching works well for loads with a long thermal time constant, such as heaters, but Im not sure I understand
what PWM has to do with this.
Zero cycle switching takes place at the frequency of whatever the mains is , usually 50 or 60 hz , and has to be syncronised
with the zero crossing points of the mains voltage.
You could make a zero cycle switcher fairly easily with an Arduino, but it wont be using PWM.
178  Using Arduino / Motors, Mechanics, and Power / Re: Solenoid valve 12V on: December 02, 2013, 07:32:19 pm
That looks like a normal solenoid valve, which needs power applied to turn the valve on.
No power and the valve turns off.
Dont think thats what the OP wants.
Ive never seen a latching type of water valve, although you could get close with a rotary water valve, but they are usually
a lot more expensive.
179  Using Arduino / General Electronics / Re: MOSFETs to switch/cut-off 10000V on: December 02, 2013, 04:32:05 am
The capsense library wont work in an application like this , as it requires a very high impedance from what is being sensed to ground.
The sense resistor needs to be somewhere between 100K to 50 M ohms  which means that the leakage resistance to ground has to be at least this high or higher.
In the example application, ie detecting a persons hand it will work fine , as the sensing plate is has extremely high resistance to ground , so very small changes in capacitance can easily be detected.
That principle wont work for a very long wire , with a large number of insulators supporting it , as every insulator represents a parallel capacitance to ground and a shunt resistance to ground.
They all add together and will totally swamp any small changes caused by a capacitance change along the wire.

180  Using Arduino / General Electronics / Re: MOSFETs to switch/cut-off 10000V on: December 02, 2013, 01:53:49 am
How is the Arduino detecting that something has touched the fence , when the fence isnt energised.
Simply measuring resistance to ground wont be in any way reliable, as electric fences always has some residual
leakage current, which gets much higher when the fence gets wet.
Its also directly related to the fences length, and the quality of the insulators used.
Im not clear what the OP is actually trying to do here.
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