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31  Using Arduino / Networking, Protocols, and Devices / Re: rf longer antenne on: June 09, 2014, 06:15:54 pm
Antennas need to be resonant at the frequency they are used at , which means the length needs to be 1/4 wavelength long, or an odd multiple of that length.
So an antenna 3/4 wavelength will also work, but wont be any better than a 1/4  wavelength.
Any other lengths will be worse.
17 cm is the optimum length for a 433 Mhz transmitter.
32  Using Arduino / Project Guidance / Re: Confused by softserial on: June 08, 2014, 05:26:32 am
Software Serial disables interrupts when its running, so sending from the hardware serial port to the Software Serial Port will work
but the reverse wont , as the hardware port needs interrupts to be enabled to receive data.
33  Using Arduino / General Electronics / Re: Rechargeable Battery Overheating on: June 07, 2014, 06:21:25 pm
Heres a crude method of achieving what you want.
Connect a 5.6V 3 watt or bigger Zener diode, across the battery terminals, so that the Zener starts to conduct
when the battery voltage get to 5.6 V.
NimH cells can be charged to 1.4 V per cell without them overheating. and 1.4 V is a fair approximation of the battery
fully charged.
4 cells in series = 1.4 X 4 = 5.6 V.
The Zener diode will get warm so you will nead a heatsink of some kind.
34  Using Arduino / General Electronics / Re: Project Battery Drains Quickly on: June 06, 2014, 01:16:08 am
What does the project do?
Without knowing what the power demands are , its impossible to determine how big a battery you will need to last 6 months without recharging.
35  Using Arduino / Project Guidance / Re: Need opinions / suggestions on circuit design on: May 30, 2014, 11:10:36 pm
Your biggest problem will be the design of the switching regulator.
To cover a wide output voltage range at high current such as 10 A is a very hard ask.
The biggest problem is the magnetics and getting the regulator to work properly at a low output voltage
with a high current.
Its these conditions which will cause very high peak currents to flow in the magnetics, and that involves you making sure
that saturation doesnt occurr.
Id start by forgetting the Arduino entirely, and try and design a switching regulator that will do what you want.
36  Using Arduino / Networking, Protocols, and Devices / Re: Apc 220 Wireless module don't working on: May 24, 2014, 07:26:52 pm
Im a bit lost here.
Where is the other radio module.
You need 2 , one to transmit from and the 2nd to receive .
Those modules are 1/2 duplex, they can send or receive , but not do both at the same time.
37  Using Arduino / Motors, Mechanics, and Power / Re: Arduino control mains device on: May 23, 2014, 02:14:40 am
What kind of electric water heater is involved?
If its a hot water system, then the heating elements in these heaters are usually 3600 watts, so you will need
a relay with a 15A rating.
38  Using Arduino / Project Guidance / Re: how to interface RF433mhz modules to arduino on: May 22, 2014, 09:40:36 pm
Simplest way is to use an SC2262 encoder at the transmitting end and a SC2272 decoder at the receiving end.
Just connect the encoder to the transmitter, and the decoder to the receiver, and connect the Arduino to the 4 data output pins of the decoder.
39  Using Arduino / Networking, Protocols, and Devices / Re: Decoding 433mhz remote signal on: May 22, 2014, 08:18:11 pm
An FM transmission into an OOK receiver will just look like a permanent carrier, which will give a permanent logic 1
on the data pin.
Your method is about the only way forward if you identify the remotes chipset.
If you have a scanner that can tune to 433 Mhz , you may be able to get a crude idea of what the remote is sending
as most scanners have FM demodulators, but it still doesnt help as you will need an FM transmitter.
40  Using Arduino / Networking, Protocols, and Devices / Re: Decoding 433mhz remote signal on: May 22, 2014, 06:36:08 pm
Sounds like the remote is using FM , which is incompatible with your 433 Mhz receiver.
Only sure way to find out is to pull the remote apart and try and indentify what chipset its using.
41  Using Arduino / General Electronics / Re: How do you measure the duty cycle of sinus with a arduino uno? on: May 16, 2014, 01:56:18 am
A buzzer will produce a complex waveform with a lot of harmonics in it , which will make it difficult to measure
unless you filter out all the harmonics and just leave the fundamental, which will be a sine wave and easy to measure.
42  Using Arduino / General Electronics / Re: how many minutes or seconds does a RTC 1307 missing each month. on: May 14, 2014, 11:55:45 pm
The RTC 1307 uses a 32.768 Khz watch crystal.
The problem here is that the absolute accuracy is heavily determined by the crystal itself and how well
the crystal matches the parallel load of the 1307 oscillator.
The crystal specs are here

Freq 32.768 Khz.
Max series ESR  45 K.
Required Load capacitance 12.5 pf

The problem is that most suppliers of such crystals wont provide you with a datasheet so its essentially luck;.

43  Using Arduino / Sensors / Re: Very basic question about DHT11 Humidity sensor on: May 11, 2014, 06:35:11 pm
What is the application .
The DHT22 sensor is far better than the DHT11 .
As for the 2 methods which the DHT11 comes in , only 3 pins are ever used.
The sensor needs a pullup resistor from its Vcc line to its data line.
In the arrangement with only 3 pins supplied , the pullup resistor and usually bypass capacitor are supplied.
44  Using Arduino / General Electronics / Re: battery charging... on: May 05, 2014, 12:23:43 am
What do you mean by 0.5v above its charge level?
How are you going to measure the charge level whilst charging?
45  Using Arduino / General Electronics / Re: Power supply from ATX PSU on: May 04, 2014, 08:06:45 pm
The 12V rail resistance reading is wrong.
It should read around the same as the 5V rail resistance.
It looks like either a shorted capacitor or a shorted diode for the 12V rail.
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