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226  Using Arduino / General Electronics / Re: Tachometer vs GPS on: July 25, 2013, 04:38:56 am
A tachometer measures engine RPM.
Its not a speedo or odometer.
Even a speedo relies on a fixed known relationship between wheel speed and tyre size.
227  Using Arduino / General Electronics / Re: Tachometer vs GPS on: July 25, 2013, 01:09:43 am
Your question makes no sense.
A tachometer in a car measures the engine RPM.
To then determine the cars velocity requires additional input, such as the relationship between the
engines RPM and the wheel speed.
The cars velocity then requires information about the  tyre circumferance.
How accurate the speed is , depends on the accuracy of all this information.
228  Topics / Home Automation and Networked Objects / Re: Kambrook Remote Power Outlet & Arduino - working on: July 24, 2013, 04:57:12 am
Hi there.
Id appreciate the codes if possible.
I started doing what you have done last week, but no point reinventing the wheel.
Ive also decoded some remote control power points that Magnet Mart sell.
4 channel based on SC2262 / SC2272 chips .
My email is
229  Using Arduino / General Electronics / Re: Super mains hum detector.... on: July 23, 2013, 12:48:05 am
What you are trying to do is extremely difficult.
The problem is what is electrical noise?
Electrical noise is everywhere, not only when there is mains power connected to your house.
Unless you lived somewhere like the middle of nowhere, with nothing anywhere near you, you will always
pick up some kind of electrical noise.
If you try to detect only the mains frequencies like 50 or 60 hz, this will only work when your detecting device
is very close to a power carrying wire in your house, like a few inches away.

230  Using Arduino / Project Guidance / Re: Getting into radio on: July 23, 2013, 12:40:02 am
A better solution is to start by making yourself a simple radio receiver.
Its easy to make a simple crystal set that will receive AM radio stations.
This will teach you some basic fundamentals about tuned circuits and diode detection.
Here is a simple example of how to make one.
You could optionally add a small audio amplifier to drive a small speaker.
231  Using Arduino / Project Guidance / Re: Sniffing from 433 MHz receiver module on: July 22, 2013, 06:50:21 pm
Those cheap 433 Mhz modules are simple ASK receivers.
They dont know anything about baud rate.
What you are seeing on the data out pin is the digital equivalent of broadband noise
combined with whatever 433 Mhz signals there are in your area.
Unless you know specifically what you are trying to look for , its not possible to simply decode
whats coming from the data out pin.
Most applications that use these radios transmit known easily identifiable sequences that are easy to
find and decode, but you still need to know what they are.

232  Using Arduino / Project Guidance / Re: Getting into radio on: July 21, 2013, 10:48:22 pm
Building Radio Transmitters that actually work, ie have efficiences of 50% or more is not a trivial
exercise, and requires a good understanding of impedance matching networks , and an understanding of antenna design.
The ARRL handbook is not a bad start, but the learning curve is steep.
If you are looking at building Transmitters in the UHF or SHF bands , 400 Mhz up to 2.4 Ghz
I would say forget it initially, as its not usually practical for a home hobbyist.
233  Using Arduino / Motors, Mechanics, and Power / Re: 25A Solid State Relays Keep Failing on: July 19, 2013, 07:00:01 pm
You need to use zero cycle switching so that the current spike problem is avoided.
This involves turning the SSR on when the AC waveform is at or close to its zero point in the AC cycle.
This way the initial current surge is avoided.
Its likley you are exceeding the di/dt rating of the SSR , by switching it on at or close to the peak of the AC cycle.
This would explain why the SSR does work for some time then fails.
All solid state switches not only have a maximum current rating, but also a maximum di/dt or rate of change of current with time rating.
The latter is usually not a problem with resistive loads, but becomes a problem with reactive or inductive loads.'
234  Using Arduino / General Electronics / Re: Crystal behaving badly on: July 18, 2013, 07:03:07 pm
The oscillator is a parallel mode type, and the impedance on the input side is very high.
Its likley that the CRO probe is causing the oscillator to stop when you probe the input side.
You should also have the parallel caps installed .
235  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.
236  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.
237  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.
238  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.

239  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.
240  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.
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