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181  Using Arduino / Sensors / Re: how to make real antenna for an RF module ? on: July 17, 2013, 06:21:21 pm
Most simple commercial antennas are nothing more than a length of wire inside a plastic sleeve.
They may have loading coils or impedance matching networks if the wire length is not a multiple
of a 1/4 wave long .
Some longer antennas can be made of fibreglass rods with the wire being a copper braid placed over the rod
and encapsulated in thin epoxy.
182  Using Arduino / General Electronics / Re: Odd behaviour: Solar charging voltage crash mid-day on: July 16, 2013, 05:58:29 am
When Solar panels get hot,the output voltage drops.
Could that be the problem.
183  Using Arduino / General Electronics / Re: Solar power question on: July 15, 2013, 03:41:22 am
MPPT without a battery simply doesnt work.
Trying to run a pump off a solar panel by itself wont work either
unless the capacity of the solar panel is so big that it can supply the pumps start current
in the low light conditions early in the morning.
You need a battery in between the solar panel and the pump.
184  Using Arduino / Networking, Protocols, and Devices / Re: Ethernet Shield + RF 433 Mhz receiver on: July 12, 2013, 07:22:32 pm
How old is the garage door?
Most garage door openers use rolling code receivers for security.
You will find it very difficult to simulate with a Arduino.
You can do it by using the Arduino to simulate the button pressing of the garage door remote
but this requires the disassembly of the remote.

185  Using Arduino / Project Guidance / Re: Wireless communication on: July 12, 2013, 07:09:34 pm
The ability of RF to penetrate walls and obstructions depends a lot on the frequency used.
Essentially the lower the frequency the more hope you have.
The very cheap low power radios are 433 Mhz which will have more chance than the better 2.4 Ghz radios
but experimenting is about the only way to find out.
Using walkie talkies will give you a false outcome as they generally use a much higher power output
than small data radios.
Id be inclined to use EOP (Ethernet over Power) if there are power points in both locations.
186  Using Arduino / Project Guidance / Re: Approaches to measuring power consumption on: July 09, 2013, 11:45:48 pm
How accurate do you want the power measurements to be.
Inductive pickup clamp type devices arnt very accurate as they dont know anything
about phase angle, so cant tell the differance between watts and VA, and they only work with
sinusoidal current waveforms, so will be inaccurate with loads with switchmode power supplies.
The only accurate way to measure power consumption, is to both measure the voltage and current
and compute the RMS value of both to obtain the power.
There are dedicated ICs available that do all you need, like this.
http://www.maximintegrated.com/datasheet/index.mvp/id/7080
187  Using Arduino / Sensors / Re: troubleshoot DHT22 Humidity sensor on: July 09, 2013, 02:35:42 am
The sensor in the diagram looks like a DHT11, not a DHT22.
The sensors are similar, but the decoding code is not.
188  Using Arduino / Sensors / Re: troubleshoot DHT22 Humidity sensor on: July 08, 2013, 02:51:56 am
Without a diagram of how the DHT22s are connected its impossible to answer your questions.
A timeout error means that the DHT22 is not responding to commands from the Micro.
189  Using Arduino / Project Guidance / Re: Project using peltiers to cool water on: July 02, 2013, 06:42:46 pm
Peltier coolers in cooling mode are pretty inefficient, around 30% - 50% at best.
The issue is how well you can get the heat away from the hot side of the peltier
and the usual way of just connecting a heat sink with a fan doesnt work all that well
unless you have lots of air which means big fans.
Using a heat pipe is a better method , but makes the system more complex.
190  Using Arduino / Project Guidance / Re: Feasibility of a temperature controlled power outlet? on: June 30, 2013, 07:09:08 pm
Need to be careful with air conditioners that you dont turn them on and off frequently as this can damage the compressor.
The thermostat in air conditioners has an inbuilt timer built in that makes sure that the compressor doesnt get turned on and off
at a rate thats too frequent, usually around 3 - 5 minutes.
This time is to allow the gas pressure on the high side of the compressor to slowly equalise with the pressure on the low side so that the compressor
isnt trying to start with a load.
191  Using Arduino / General Electronics / 12V Lipo battery question. on: June 29, 2013, 10:49:50 pm
Just about to buy one of these things for my standby solar power system to replace the Lead Acid battery and
it struck me , how do you get 12 V from a LIPO battery, given the 3.7 cell voltage.
Or are these batteries really 11V but quoted as being 12V.

192  Topics / Device Hacking / Re: 2 way radios as transmitter and receiver on: June 28, 2013, 07:34:22 am
The major issue you need to address is what data rate do you need to control the robot.
2 way radios are very slow in sending data because they are 1/2 duplex, ie you can send or receive
but not both at the same time.
Ensuring that what you send actually gets to the other end is a complex process involving sending then receiving
then sending again.
The actual data thruput can be as low as 100 bps , even if the radios can go faster.
With unmodified radios you are limited to around 1200 bps .
Going faster needs modifications to the radios which normally you cant do unless you have the circuits of the radios.
Id be looking at using broadband wireless using the cellular radio system to get more speed and reliability.
193  Topics / Home Automation and Networked Objects / Re: Signal on 230AC on: June 27, 2013, 12:06:33 am
Use a pair of EOP (Ethernet over Power) adapters like these.
http://www.pccasegear.com/index.php?main_page=product_info&cPath=200_1348&products_id=19316&zenid=9cbc940f0092ece65946acebf302de25
Many differant brands and models of these devices.
Range is usually around 300 feet.
Ethernet shield on 2 Arduinos plugged into the EOP adapters will do what you want.
No need to play around with the Mains.

194  Using Arduino / Project Guidance / Re: RF module on: June 26, 2013, 05:16:10 am
The data format for the hs2260 encoders and decoders is well documented and there are some Arduino libraries
that can possibly decode them.
Have a look at the RC switch libraries.
Unfortunately, whilst the data format is standardised, the data rate is not and varies between suppliers.
You will have to measure the data rate somehow.
Its easy if you have a CRO.
195  Using Arduino / Project Guidance / Re: RF module on: June 25, 2013, 05:33:07 am
Need to know more about the remote.
What exactly does it send when you press a button.
The sketch seems to be designed for a particular type of transmitter.
 
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