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136  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.

137  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.
138  Using Arduino / General Electronics / Re: MOSFETs to switch/cut-off 10000V on: November 29, 2013, 06:01:47 pm
This is an interesting read about high voltage thyristors which can switch 10Kv at up to 5000 A.
Devices like this are used in HVDC converter power stations where the HVDC can be as high as 800 KV.
People who work in this industry I really have high regard for.
Getting it wrong yields some horrible outcomes.
http://www05.abb.com/global/scot/scot221.nsf/veritydisplay/1402c60973f47e72c1256fda004aead8/$File/thyrvalv.pdf

Moderator edit: link corrected
139  Using Arduino / Networking, Protocols, and Devices / Re: testing 433 MHz reciever on: November 28, 2013, 04:51:26 pm
You can do some really simple tests which may help to determine whether the receiver is completely dead, but
wont conclusively indicate its working properly.
A multimeter connected to the receivers data pin should  read some arbitrary voltage between 0 and Vcc.
The voltage may wander around a bit.
This will test the receivers basically functionality.
Another test is to connect the transmitters data pin to its Vcc pin, and power it up.
Do the same test with the receiver, and it should now show a constant voltage on its data pin close to its Vcc.

The only real way to test the receiver is to use a dual channel CRO and feed data from an Arduino or any data source
into the transmitter and then check the receivers data line , which should show a very similar data waveform to what is being sent.
You cant test the receiver with just 1 Arduino.

140  Using Arduino / Motors, Mechanics, and Power / Re: *cheap* capacitor power supply 80-140mA on: November 26, 2013, 06:09:39 pm
Can be done , but not cheap.
The capacitor needed is 3 uf at 200 V, and they are quite expensive , anywhere between $6 to $12 each.
Capacitor type power supplies only make economic sense for very low current loads , 20ma or less.
Also quite dangerous , unless the item they are being used in is totally isolated.

141  Using Arduino / Project Guidance / Re: GPS accurate to microseconds on: November 24, 2013, 10:23:38 pm
Its not usually possible to phase lock the crystal oscillator in a Micro with an external referance, because theres no provision
to electronically alter the frequency of the oscillator.
You could however use an external VCXO something like this
http://www.maximintegrated.com/app-notes/index.mvp/id/2097
to provide an external clock input to the Arduino and use the Arduino as a software PLL to control
the VCXO, using a PWM output into a low pass filter, which is fed to the tuning input of the VCXO.
The only tricky part is getting the damping factor right, so that the VCXO doesnt hunt.
142  Using Arduino / Project Guidance / Re: Wake up arduino from RF message on: November 23, 2013, 06:55:51 pm
If you use the design concept that a lot of wireless door bells use you can reduce the power consumption
but not eliminate it.
A pair of AA batteries will run a 433 Mhz receiver drawing 4 ma for around 1 month.
If you use Alkaline C batteries , around 8000 mah , you can get around 2 1/2 months.
Doorbells simply use a 433 Mhz receiver and a Cmos data decoder like a PT2272/ SC 2272.
http://www.adafruit.com/datasheets/PT2272.pdf
For a simple off / on application, this is all thats needed.
The Decoder simply provides 4 bits of data which can be used to turn things on and off.
Using a encoder like a PT2262 / SC 2262 , to provide the transmitted data to the 433 Mhz transmitter is all
thats needed.
The decoder chip being Cmos, only draws around 20 ua.
You dont need an Arduino at all, which reduces drastically the power consumption.



143  Using Arduino / Motors, Mechanics, and Power / Re: what is these stuff? on: November 23, 2013, 04:57:53 pm
JimboZa is correct.
There are membrane operated water valves, which use the water pressure to operate the valve.
What the solenoid does is moves a tiny plunger to open or close a small hole which allows the water pressure
to operate the valve.
You should hear a click from the valve when the power is applied.
144  Using Arduino / Networking, Protocols, and Devices / Re: Manchester Library (MCHR3k) RF Modules & Delays (Fixed, was Noise) on: November 21, 2013, 07:10:01 pm
Use the Virtualwire library instead of Manchester.
http://www.pjrc.com/teensy/td_libs_VirtualWire.html
145  Using Arduino / Networking, Protocols, and Devices / Re: Sensing radio receiver pwm on: November 21, 2013, 07:05:31 pm
Need to know what the output data looks like.
Its most likley PPM (pulse position modulation) which is not PWM.
Consists of a sync pulse plus a number of channel pulses which vary in time.
Not easy to get an analog voltage that really means anything.
146  Using Arduino / General Electronics / Re: How can I read mains voltage with this oscilloscope? on: November 21, 2013, 04:52:36 pm
What you are trying to do is highly dangerous as USB scopes dont have an isolated earth.
This means that if you get the active and neutral the wrong way around , the scope and whatever it is plugged into, ie
what is supply the USB power, will go bang.
Use a step down transformer and look at the isolated secondary.
147  Using Arduino / Motors, Mechanics, and Power / Re: Can Arduino Uno power four 3.3 volt motors without frying the Arduino on: November 19, 2013, 09:57:45 pm
Quadcopters are getting quite small these days.
I got one of these last year to play with.
http://arkrc.com.au/twister-quad-copter-mode-1-350mm-diameter-with-3-7v-lipo-2-4g-radio/
Runs off a single 3.7V lipo, and surprisingly for its size can do some amazing things.


148  Using Arduino / Microcontrollers / Re: ATmega328 on 3.3v - strangely enough does not work... on: November 19, 2013, 06:43:21 pm
Did you change the BOD fuse in the Micro to suit the lower supply voltage.
http://www.atmel.com/Images/doc8161.pdf
See sect 28.4 which gives the fuse values for differant BOD detect voltages, or you can disable BOD altogether.
Otherwise the chip will simply keep resetting itself and wont start.

149  Using Arduino / Sensors / Re: Manchester version 1.0 libary for RX/TX temperature sensor? on: November 17, 2013, 05:42:40 pm
Have look at the VirtualWire Library.
http://www.airspayce.com/mikem/arduino/

Its used for sending short messages between Arduinos using those simple 433 ASK radios.
Im not sure whether it actually uses manchester coding, but it achieves similar results, ie no DC component
in the transmitted data.
150  Using Arduino / General Electronics / Re: Help identifying crystal please on: November 17, 2013, 05:30:21 pm
Series mode crystals will oscillate OK in a parallel circuit, but the frequency will be slightly off.
Its not enough though to worry an Arduino, unless the application requires the frequency to be exactly 16 Mhz.
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