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436  Using Arduino / Project Guidance / Re: Arduino+Relay+Wifi on: September 21, 2012, 06:44:11 am
You need to have a power supply for the Arduino, which can be batteries or mains.
The Arduino can operate a relay switching the 220V to the speakers on/off.
437  Community / Bar Sport / Re: Interstellar Travel on: September 20, 2012, 06:23:17 pm
First we need to get off the planet more easily.
The space elevator sounded like a good idea if it could be built.

This falls short of that but it is interesting that a 20km steel tower could support its own weight.
How would you construct it though?

There was an idea to build a 1km concrete tower to generate energy but I seem to remember they would have to pour concrete round the clock for years to build it.
438  Using Arduino / Project Guidance / Re: Is arduino what I need for functional art project? on: September 20, 2012, 06:01:32 pm
I don't know how to do it, but just wanted to say I like the idea. You would need a bit of distortion though any you would have to tune the radio between stations.
439  Using Arduino / Sensors / Re: motion detector that works behind clear glass window? on: September 20, 2012, 05:51:46 pm
johnwasser: We seem to have come up with the same idea, I did not see your post before sending mine.

BlueJakester: If you are going to use an IR LED check if you really can detect it though the glass. If you can then blinking sounds like a good idea, but make sure it is fast enough that a leg swinging through the beam will be detected.
440  Using Arduino / Project Guidance / Re: Hot water line flusher on: September 20, 2012, 05:43:39 pm
You have not said how you get the hot water. That is critical. If you have a tank of hot water that is already hot then how fast it gets to you is down to flowrate. If you have a boiler that heats the water when there is a demand then that is a completely different problem, and in fact a slow flowrate (at least initially) may be your friend.

Imagine you have a boiler full of cold water. You open your faucet as far as it will go wanting hot water. The boiler switches on and tries to heat the water to the desired temperature but there is a huge flow of cold water coming into it and it struggles to raise the temperature.

What you really need is a valve near the boiler that only opens fully when the water is warm. So: you turn on your faucet, boiler heats water (only a little flows out), water get warm, valve opens hot water flows down pipe, boiler manages to keep inflow upto temperature. A radiator valve on a vehicle gives the general idea.

To do it manually turn the faucet on slightly so that the flow is enough to start the boiler, wait until you get hot water, then turn up the flow. If you time this I am sure you will find you get hot water faster but wasting less water and power.
441  Using Arduino / Sensors / Re: motion detector that works behind clear glass window? on: September 20, 2012, 05:23:33 pm
I agree with the comment about IR. I tried taking pictures using an infrared camera looking out through a window. What it picked up were reflections of heat sources inside the room on the glass but not what was outside.

Maybe this is a doge but if you can put small mirrors outside then you could reflect a light off them and detect the reflection. If the 'beam' was cut you could alarm.
442  Using Arduino / Project Guidance / Re: Arduino Rocket Ejection at Certain Altitude on: September 20, 2012, 05:17:18 pm
Lets say you had ground sensing radar in the rocket, the reading you got would still depend on your attitude and if you were at an angle you could not be sure you were not above some prominent feature. It sounds like a simple problem, but it seems really difficult. Quite obviously the Curiosity landing is a fake   smiley-twist
443  Using Arduino / Project Guidance / Re: Bathymetry Measuring Apparatus on: September 20, 2012, 04:05:18 pm
I am a geoscientist trying to build a device that will measure the depth of the water and correlate the measurement with a lat/long through a GPS receiver.

You should try to be more precise about what you want to do. Most ships have depth sounders and navigation equipment. Are you trying to integrate readings from these? On the other hand the subject line Bathymetry suggests a submersible vehicle, so are you trying to measure its depth, or the depth of water it is in?

As you can see these are very different problems and there are probably loads of different interpretations that can be put on what you wrote. First rule is to try to be precise about the problem and what you want to achieve.
444  Using Arduino / Project Guidance / Re: Arduino Rocket Ejection at Certain Altitude on: September 20, 2012, 12:32:18 pm
I was walking again with a hand held GPS. I started at sea level (above high tide) and I went to a point (a gate) where I had previously noted my altitude. The reading I got was 80m but the previous time, at the same spot, it was 89m, a 9m difference. At the end of the walk I noticed that at some point I was supposedly at -1.8m, though I never went for a swim  smiley

The only thing I can think of to account for the 9m was that I was walking at a different time and so possibly triangulating with different satellites. I just looked up Garmin (it was not Garmin I was using) and they say their receivers are accurate to 15m on average. I was expecting 5-10m.

This does show the problem of trying to measure a 'true' altitude to +/- 10".

Point taken about the rope, shows how careful you have to be with requirements specifications.
445  Using Arduino / Project Guidance / Re: Arduino Rocket Ejection at Certain Altitude on: September 19, 2012, 10:04:52 am
So what will give you a "true" 750'?
I think that is quite a hard thing to do. Constantin's rope will not work becuase the rocket could be flying horizontal. Barametric pressure probably reads a lower pressure i.e. higher altitude than true because of the venturi effects PeterH pointed out.

Knowing acceleration and attitude you might be able to calculate altitude?
Perhaps a laser rangefinder?

To get a true reading within 10ft sounds difficult to me.
I was using a handheld GPS last night and my altitude was shifting around by a couple of meters for no obvious reason. That is why they use a standard device in competitions I think.
446  Using Arduino / Project Guidance / Re: Arduino Rocket Ejection at Certain Altitude on: September 18, 2012, 04:50:52 pm

I tend to agree with PeterH's thoughts but if this is a competition then this may be the important point;
where such an altimeter is the official altitude recording device

So the rocket has to perform at 750ft +/- 10ft as measured by the official device.
That does not mean it is actually happening at a true 750ft.

447  Using Arduino / Project Guidance / Re: Getting Started: Sensors and Displays for a manual wheelchair on: September 18, 2012, 04:28:23 pm
My daughter has been in and out of the chair for a few months while recovering from simultaneous injuries to BOTH ankles
- Ouch, I hope she makes a good recovery.

will get some technical advice from long term chair users. For some of them, this will be the first time they have ever been asked for advice.
As a non-user I admit I was a bit sceptical about the signaling options but the point was to ask so if that is the feedback go for it.

The GPS idea is a bit advanced because of the display requirements if you go down the mapping route, but speed distance etc. would be feasible.

Sail: You are right, that would be cool, but not really an Arduino project.
It was a wild idea, and you did ask for ideas. It might not be totally daft though and maybe not totally outside the limits of an Arduino. In fact I may just have devised a new paralympic sport. Imagine a sand yacht where the sail is motor controlled.

Here is a link to bicycles with sails, I know we are stretching the topic of your post but you may find it of interest.
The Dutch seem to have been the first to put sails on bikes
448  Using Arduino / Project Guidance / Re: How to transmit data underwater? on: September 18, 2012, 09:51:21 am
Power considerations might determine if you need some sort of umbilical.
If you do then that brings wired communications into play.

Using a buoy has the advantage of letting you know where your ROV is and
helping you get it back in the event of disaster.

On the ultrasonic front I would have thought if you could reliably transmit and receive two different tones you could make
something work. You could use Biphase Mark Code which means you send out half-bits. This coding has the advantage that even
if your data were to contain long strings of 0 or long strings of 1 the half bits sent change continously.
If you can sample much faster than the half-bits then it is easy to synchronise on them,
you don't need a clock signal. You do also need to have some way to recognise the start of a message and a checksum
might be wise.
449  Using Arduino / Project Guidance / Re: Getting Started: Sensors and Displays for a manual wheelchair on: September 18, 2012, 08:45:21 am
If you are not a wheelchair user yourself it might be an idea to ask somebody who is what they would like. There may be age related differences. I could be on completely the wrong tack but perhaps some kind of gps / fitness setup might interest younger people, akin to what you can get for bikes (maybe a bit advanced for Arduino though).

You can actually get bicycles with sails now, that would certainly be something on a wheelchair, but I am getting carried away 
450  Using Arduino / Project Guidance / Re: garagedoor on webpage with webcams on: September 17, 2012, 08:23:46 am
You probably need to flesh out your specification a bit.

Who will use the webpage, is it a security guard who opens the door when he sees somebody on the webacam?

Does the webcam need to provide video or just still photographs?

You have to use an arduino, but for what, does it have to do everything or might it just open and close the door on comand from a PC that had hosts the webpage and has the webcam feeds?
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