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166  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.
167  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.


168  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.

169  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.
170  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.
171  Using Arduino / Sensors / Re: UFO hunting lead to a cool idea: Inertial Path Tracking on: November 12, 2013, 05:50:36 pm
All inertial guidance systems suffer from a problem known as integration drift, which causes over time
an error in the location the device provides.
The error gets worse the longer the device is used.
The error can be to some extent minimised by using very high quality gyros and accelerometers, but costs then become very significant.
This article gives some more info on the subject.
http://www.navlab.net/Publications/Introduction_to_Inertial_Navigation.pdf
172  Topics / Home Automation and Networked Objects / Re: 433 MHz RF transmitter questions on: November 10, 2013, 04:45:12 pm
Its important that the supply voltage for those el cheapo 433 Mhz receivers is as close as possible to 5V.
The frequency stability of the onboard oscillator which sets frequency isnt all that great and drifts with variations
of supply voltage, which causes the receiver to appear to be insensitive .
Measure the voltage with a multimeter right on the receivers supply pins , especially if the receiver is being powered
from a power source which also has to power other things.
173  Using Arduino / Networking, Protocols, and Devices / Re: 433mhz RF modules on: November 09, 2013, 05:58:27 pm
What type of wall sockets are you trying to sniff
The Arduino RF switch library only works for devices that use the SC2262 / SC 2272 type decoding chips.
Not all wall sockets however use these chips.
174  Using Arduino / Project Guidance / Re: Wake up arduino from RF message on: November 09, 2013, 05:45:08 pm
Its not possible to make 433 Mhz receivers with extremely low power consumption, as most of the power goes into running
the oscillators and the RF amplifier.
There are some tricks you can use to reduce the power consumption however, which are commonly used in battery operated
weather stations.
It relies on knowing when the transmitters are likley to transmit and then turning the power to the receiver on and waking up
the Arduino from sleep for a short time .
For example, suppose you want to transmit data every minute.
You turn the Arduino on and the 433 receiver and wait until you get a valid transmission.
You then put the Arduino to sleep but keep time by using a low power 32.768 watch crystal.
When a minute has elapsed, you wake the Arduino up and supply power to the receiver.
This technique works , if the data to be sent is small , and comes at known time intervals.
175  Using Arduino / Sensors / Re: WIND SENSOR / ANEMOMETER on: November 06, 2013, 06:42:19 pm
You will have to pull the anemometer apart to see what type of sensor pickup it uses, otherwise you dont know
whether the voltages coming from the anemometer are even compatible with the arduinos input.
A common technique thats used is a spinning magnet which induces a small voltage into a pickup coil.
This produces an AC output which has to be conditioned so that the Arduino can read it.
176  Using Arduino / General Electronics / Re: Rectification Circuit (receiver of wireless power transfer) on: November 04, 2013, 04:36:52 pm
How far apart are the coils?
Most inductive charging systems need very closely coupled coils spaced only a few mm apart.
Hard to know what needs to be changed without more information about the primary coil circuitry.
177  Using Arduino / Project Guidance / Re: Transfer of charge wirelessly via inductive coupling on: November 03, 2013, 03:20:30 am
Ive repaired a number of Braun electric toothbrushes which use a close coupled inductive loop in the base of the toothbrush to charge the internal AA battery.
The oscillator in the charging base runs at 50 Khz and consumes 1.3 watts.
The power delivered to the battery charging cct in the toothbrush is 25 mw.
The coils are extremely close , around 3 - 4 mm spacing.
1.3 watts in for 23 mw out isnt very good , but in an application like this , the efficieny doesnt matter.
Trying to scale the idea up though , is very hard .

178  Using Arduino / Motors, Mechanics, and Power / Re: Need help on powering micro servo motor with 3.7 Li-ion battery? on: November 02, 2013, 12:43:53 am
Whats the current draw of your flashlight?
The capacity of a Li battery and indeed most other batteries is stated for a discharge rate of 1/20C .
At higher discharge rates , you will get less capacity.
179  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.
180  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.
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