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1  Using Arduino / Project Guidance / Re: Simple foot scanner using Arduino. on: November 06, 2013, 07:54:30 am
As a first step you should decide what resolution you need the measurement to be to. Then calculate how many sensors you will require (I expect it might be ~500). If you think it practical to wire up that many sensors the next step would be to identify a sensor of the required size and performance and, assuming you find one calculate the cost.

A mat is flexible, I doubt this device will be like a mat, at best it will be a solid board.

If you don't exclude boxes then people could put their feet in the corner of a box pressed against two edges (to keep the foot square with the box) and you could then scan the length and width width of the foot with two lasers and two LEDs moved by stepper motors.
2  Community / Bar Sport / Re: How tall can we build? (and Voltage Differential of Earth) on: November 05, 2013, 09:50:57 am
The Dyson-Harrop Satellite does not rely on the push of the solar wind instead it extracts electrical energy from the plasma
A relatively small Dyson-Harrop satellite using a 1-centimetre-wide copper wire 300 metres long, a receiver 2 metres wide and a sail 10 metres in diameter, sitting at roughly the same distance from the sun as the Earth, could generate 1.7 megawatts of power – enough for about 1000 family homes in the US.

Apparently it is practical to build one of these the main issue seems to be how to get the power from the satellite back to Earth using lasers. No doubt it is not quite that easy but "This satellite is actually something that we can build, using modern technology and delivery methods," Harrop says.
3  Using Arduino / Project Guidance / Re: Time synchronization between arduinos ? on: November 05, 2013, 09:34:23 am
You might want to consider if you need to handle daylight saving time. If you do then once a year you will have a gap of an hour, and once a year an hour will happen twice. Much better to avoid daylight saving if you can.
4  Using Arduino / Project Guidance / Re: I know this might be very a stupid question but... on: November 05, 2013, 09:15:43 am
Get a starter kit that provides components, circuit diagrams and sketches. You will know that the mini-project should work which makes it easy to find your errors. Once you have the supplied example working make your own variations to it - you will learn a lot.
5  Community / Bar Sport / Re: How tall can we build? (and Voltage Differential of Earth) on: November 05, 2013, 08:22:33 am
I remember buying military surplus micro fine twin wire from guided missiles, many moons back, I wonder if any voltage was generated if they were fired from aircraft.

I am sure a voltage would have been generated. When they work on overhead powerlines they diconnect them but also earth them as wind blowing through the cables can generate enough static to be dangerous.

On a bit of a tangent there is a video on youtube of a guy climbing out of a helicopter to work on a live overhead line!

The satellite wire works because the wire is moving through the Earth's magnetic field - great idea, wonder who thought of it.

The Dyson-Harrop Satellite uses the solar wind.

6  Community / Bar Sport / Re: How tall can we build? (and Voltage Differential of Earth) on: November 04, 2013, 11:15:44 am
What you really need if you want power is a Dyson Sphere to generate ~4 x 1026 W . If you cannot build that then keep up with the intergalactic neighbours by at least getting a half decent Dyson-Harrop Satellite;

Another essential is a space elevator. The problem with building that is that all known materials will be crushed under their own weight. However if you put a lump of rock into orbit round the Earth you could "drop" a line from it and keep it under tension rather than compression. Not sure how this stands up to winds etc. or what would happen if somebody cut the rope!
7  Community / Bar Sport / Re: Don't know who Cree is?..... on: November 04, 2013, 10:39:35 am
Is anybody else fed up with energy saving bulbs or is it just me?

It used to be a bulb was a bulb and there were only about four types of fitting. Now there are zillions of different fittings so finding the right bulb for your lamp can be a pain.

Also while the bulb itself may save energy the lamps now don't take just one bulb they take four or more. I also really cannot believe that those bulbs that contain mercury etc. are going to be dillegenty recycled - they will be tossed in with the general waste.
8  Community / Bar Sport / Re: I wonder what proportion of Arduino hobbyists solder? on: November 04, 2013, 10:22:28 am
I do have a soldering iron but I mainly use it to burn my fingers.

Presumably the satsfaction comes from having "tamed the beast", i.e. it does what you wanted it to do.... Soldering or breadboarding is just a choice of assembly

That is it for me. I don't have electronics knowledge or skills but I get a kick out of writing a program that has a physical effect. Plugging components into a breadboard satisfies my requirements, though if I have to I'll burn my fingers, the components and the table.

You have not said what your kits are for Pico. If they are "learner" kits of some sort and I wanted one then I would have a go at self assembly. I would get some satisfaction from that but it would be fairly limited as I would probably not understand the electronics - it would be like painting by numbers.

If the kits provide a function (such as motor shield) then I would probably want to buy the board ready made.

I suspect you will get extra customers if you include pre-assembled as an option.
9  Using Arduino / Project Guidance / Re: Need help with a science fair project on: November 04, 2013, 08:22:21 am
What materials will you be measuring the speed of sound through?

It might be an idea to cheat a little bit and lookup the speed of sound in those materials to make sure the system you build is capable of detecting the differences.

Also will your speaker have a delay beween you outputting a sound and the speaker actually producing it?
10  Using Arduino / Project Guidance / Re: Power requirement for robot on: November 04, 2013, 07:46:20 am
Power is the rate of energy delivery.  Power is measured in watts, energy in Joules.
- oops indeed, what a stupid mistake, thanks for correcting it.
11  Using Arduino / Project Guidance / Re: use arduino to help my daughter on: November 04, 2013, 06:58:44 am
My problem with this theory is that the foot will be being accelerated in three axis and some of these accelerations will be along the axis that the tilt switch is sensing. As I see it, whenever the foot is off the ground the tilt switch is effectively useless. It's just not sensing what we want to sense, which is which part of the shoe is touching the ground.

A doubting Peter smiley
Try taking another look at this video;

To me it looks as if, when the child is walking on tip-toe, the sole of the foot is constantly making an angle of 60deg (or at least 45deg) to the floor. That is really quite an unusual way to keep your foot, which made me think a tilt switch might do the job.

When I was messing about with my multimeter I had the tilt switch arranged so that with the foot flat on the floor the switch was closed with the contacts pointing down towards the heel. Forward and upward accelerations would therefore tend to keep the switch closed.

12  Using Arduino / Project Guidance / Re: Need Help project on: November 01, 2013, 11:03:18 am
Is English your first language?
I really cannot understand what you have written.

You should try to write your problem down more clearly and include your code (use the # button).
13  Using Arduino / Project Guidance / Re: use arduino to help my daughter on: October 31, 2013, 04:44:22 pm
Okay, made a bit of progress.
Despite the veils between the realms thinning I was unable to obtain a child on which to experiment  smiley-twist

As a result I had to conduct a test on myself. There were some strange looks, but no comments, as I padded around barefoot with a buzzing multimeter in my hand and a mercury switch stuck to my heel with a big blob of blu tack.

The results were reasonably encouraging. Unfortunately it was not possible to walk on tip toe without generating transients as I had hoped, however it seemed as if I could obtain two distinct and simple signatures.

For normal walking the multimeter buzzed more or less continuously (i.e. tilt switch contact made) with brief gaps when my foot impacted on the ground.

For walking on toes the inverse appeared to happen. The multimeter was silent more or less continuously (i.e. tilt switch contact broken) with brief buzzes when my foot impacted on the ground.

The mercury switch I managed to get hold of is sensitive in 2D so the 'ball' type switch I have ordered (currently out of stock) may in fact be better.

This was a very quick test and I am not sure how clean the two signatures are but I think it should be possible to tell them apart in software. The results for a child will be different. A child's smaller feet and shorter legs will move with a different rhythm and their lesser weight will result in less jarring on foot impact.

The system will be quite sensitive to getting the angle of the switch correct I think. More experimentation required.

14  Using Arduino / Project Guidance / Re: use arduino to help my daughter on: October 31, 2013, 11:30:15 am
I'm struggling to see how a tilt switch would work on a moving foot - I think you might find it difficult to eliminate all the transients caused by movement of the foot. The pressure based approach would seem inherently much more reliable.

The idea is that 25% of the time when the child walks on her toes she will do so for X seconds or more without generating any spurious transients. I am hoping that X will be 5-10s or more. If she does that she will get a reminder, probably a vibration, to stop the habit.

If transients occur during the other 75% of toe-walking incidents that is fine, no reminder will be given. You don't want to remind the child every time, you just want to give them a nudge now and again, otherwise they will just depend on the system and will not think for themselves.

Of course this theory may well crash and burn when tested.

The pressure based approach is a good one, but I think it would be harder to turn into something small and stand alone (i.e. no Arduino).
15  Using Arduino / Project Guidance / Re: Power requirement for robot on: October 31, 2013, 08:12:31 am
Sorry still not sure how to calculate all this power stuff, if you could help with that part too id appreciate it

Lets see if I can get this right;

Power is measured in joules (J).
But obvioulsy you can apply power over a long time or over a short time.

Energy is measured in watts (W).
A watt is a joule/s i.e. it is a measure of how fast power is being supplied.

Electric charge is measured in coulombs (C)

Electric potential is measured in volts (V).
A volt equates to a J/C

Current is measured in amperes (A).
An ampere is a coulomb/s C/s

From the above you can see that 1V x 1A
is 1J/C x 1C/s or 1JC/Cs or 1J/s i.e. 1W
(so volts times amps gives watts)

When looking at batteries you want to know how many amps they can supply for how many hours.

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