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1  Using Arduino / Project Guidance / Re: Ball and socket joints/hinges? on: February 18, 2011, 10:21:42 pm
Oh awesome, thanks ( again smiley-grin )

Even better, I didn't even think of something like their 'Ultra Flexible Positioning Arms'. These would be even more suitable
2  Using Arduino / Project Guidance / Ball and socket joints/hinges? on: February 18, 2011, 10:10:07 pm
I wasnt really sure where to put this question, but does anyone know of anywhere I can buy 'ball and socket' joints?

Im not sure they even exist as such.
But Im hoping to find something like a plastic or aluminium sphere with a screwable arm coming out of it.
The sphere sits within a spherical casing (which can be screwed to a flat surface), allowing you to position the arm it so it points at any angle.

I tried my DIY shop but he was a bit clueless,suggesting I used a bulky metal huge kitchen cupboard hinge smiley-grin
I also tried a lighting shop, and they understood what I meant (kinda similar to the way spotlights can be pointed anywhere), but weren't really sure where to source them from.

Im sure many camera tripods have a similar sort of socket, but so far no joy

Any ideas please?
3  Topics / Robotics / Re: new member,, new robot on: February 18, 2011, 10:02:01 pm
What difficulties are you having exactly?

I doubt I can help, myself, but I imagine its the first question anyone with more experience is going to ask..
4  Topics / Robotics / Quiet servo's ? on: February 18, 2011, 09:58:43 pm
Are there any servo's that dont sound like a bone being crushed in a mincing machine?

All the ones I've used are loud and pretty horrible to listen to.
Surely there are some nicely slick lubricated ones which dont rely on dry cogs grinding against each other ?
5  Topics / Robotics / Automated Pet feeder/waterer on: February 18, 2011, 09:55:58 pm
Id love to build an automated pet feeder for my cat.

Not because Im lazy (ok maybe just a bit), but there are times when Im going away for just 24 hours, and its a bit of a hassle driving 10 miles to the cattery each time.

What Im thinking is some 10 inch pvc tubing filled with tasty biccies, with some sort of servo at the bottom, and an arduino controlling timing. Every 5 hours it rotates the servo, allowing a payload of deliciousness to drop into the bowl below.

For water, its less of an issue really, since my cat isnt going to drink a full bowl of water in 24 hours. But it would be cool to do water too. Maybe a similar sort of setup with a water float gauge to allow the bowl to remain filled.

Not looking for exact instructions on how to do this, just wondering if anyone has built something similar, or has other ideas on how best to do it?


6  Using Arduino / Project Guidance / Re: PWM within an arduino interrupt ? on: February 18, 2011, 09:47:37 pm
Its reassuring to know what Im trying to do isn't just a load of nonsense smiley-grin

Theres already a mosfet in my circuit, but Ill be honest, I didn't really understand its function.
Ill read up a lot more on mosfets now that I know its heading in the right direction.

Thanks for your invaluable help smiley
7  Using Arduino / Project Guidance / Re: What is the red wire for (connected to nothing on the board) in the 1st example? on: February 18, 2011, 09:45:27 pm
If its any consolation, I suffered from the same confusion with Sparkfuns breadboard templates :-D

Even their 'breadboard tutorial' has the same ambiguity, which is a shame because overall Im really impressed with Sparkfun as a company.
8  Using Arduino / Project Guidance / Re: PWM within an arduino interrupt ? on: February 18, 2011, 09:35:25 pm
Thanks, thats interesting.

I hadn't thought of AnalogWrite(), although admittedly Im not sure how I would use this to have a transistor PWM an external power source
Im guessing I can rule out Tone(), since it mentions it can conflict with PWM on pin 3, which is where my interrupt is coming from. Or maybe I can switch to a different pin?

I cant provide a nice schematic unfortunately, but the project Im working on is EyeWriter 2.
There is a breadboard sim here
and a direct image link here...

The 30Hz interrupt comes in via the PS3 eye VSYNC, which triggers every time the cam takes a full frame.
This is used to alternative an array of infrared leds around the cam, followed by two side-arrays of leds to provide 'glints' on the eye.
This is then used to capture an unilluminated image of the eye, in conjunction with a luminated image, and these are used to try and track where the pupil is, and subsequently where the eye is gazing.

What Im finding ins the rheostats are quite a big obstacle to calibrating the device quickly and easily, which is why Id like to take them out of the equation, and control them automatically via software.

Thanks for your advice so far smiley
9  Using Arduino / Project Guidance / Re: Spray can and Arduino on: February 18, 2011, 09:25:13 pm
Im curious, what it is you;re trying to protect?

But it does sound like a really bad idea to me. Kinda like rigging a shotgun to your front door.
Sooner or later, some legitimate person is gonna forget to disarm it.....

I think also that it has the same legal issues of spraying it onto the face of someone that is aggressing you.

Id really check with a lawyer smiley-wink
Defending yourself against an attack is one thing, but booby trapping a property is another.
10  Using Arduino / Project Guidance / Re: Arduino to turn on desktop PC on: February 18, 2011, 09:17:45 pm
Im all for cool projects, but I really think building a manual device to push the button on your PC is a bit much.

If your IT dept object to you leaving your PC running, they'll naturally object to you using any sort of device to turn it back on again.
More likely, they just have a general policy of remotely shutting down computers, and so if you speak to them, they will probably exclude you from this. I 'm an IT worker btw.

Failing that, It seems likely they offer some sort of remote desktop solution. You could porbably use this in conjunction with Wake ON LAN... to turn your PC back on when you need it.

A big robotic arm hovering over your power button, its gonna look real odd. Just MHO smiley
11  Using Arduino / Project Guidance / PWM within an arduino interrupt ? on: February 18, 2011, 09:04:02 pm
Lets say I have an external interrupt to the Arduino, triggering at a constant 30Hz.
At the moment, this controls two individual LED arrays, and there is a 30 Ohm rheostat on each LED array.

What Im trying to do is eliminate the rheostats (which often need twiddling), and emulate the 'resistance' via software, maybe via PWM.

But I dont think you can do PWM within an interrupt, because there is no Delay() available, and I cannot increase the external interrupt to trigger at say, 10KHz.

So what I was thinking, is maybe having a 555 timer chip, to do the PWM. I then control this from within the arduino interrupt, by turning it OFF, or ON and then programming it to emit PWM at a given (software controlled) rate.

I thought about a digital pot, but I cannot find any rated at 30 Ohms (min 150Ohms), and the the 32 step granualrity is presumably going to be too ineffective.

The other problem with a 555 timer, is that my understanding is that, Im not entirely sure how I can vary the duty cycle from between 0-100% at runtime. From what Ive read, you can wire it to have a duty cycle of < 50% with resistors+cap, but to then change it to > 50% you should rewire it with a different resistor/cap combination. So I wouldn't be able to get the full 0-100% range.

There is one final problem (as always). If I went down the 555 route, I need it to emit ~800mA. Whereas the 555 can only do 220mA, so I guess Id then need the 555 to control a transistor, with the transistor switching a 7.5V power source

I cant help thinking Im maybe over engineering this, but Id really like to remove the manual rheostats from my circuit, so they can be controlled via primitive AI in the software.

Im really interested in any other ideas how to achieve this.

Thanks smiley

12  Using Arduino / Project Guidance / Re: What is the red wire for (connected to nothing on the board) in the 1st example? on: February 18, 2011, 08:48:24 pm
In my experience (and Im certainly not any sort of expert), but I think Sparkfun create all their breadboard examples from a starting template.

This template always seems to include wires from the Arduino to the breadboard power rails by default, regardless of whether they are needed or not. I would ignore it personally, unless theres no other source of power
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