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211  Using Arduino / Project Guidance / Re: Solenoid Artistic Function - Magnet and Glass Tube on: February 01, 2013, 05:01:31 pm
I did not posted this therefore I never mentioned any dimensions of anything. The author was. If he wants to make the magnet "float" it needs to be about the same diameter to avoid spinning. By the way I wasn't answering to your post. I think I know now why Grumpy is in your name. Maybe a similar word beginning with J will describe you be better.
212  Using Arduino / Project Guidance / Re: Taking a shot at specific gravity measurements on: February 01, 2013, 04:48:20 pm
What range of specific gravity are you trying to measure? I am thinking about lowering a heavy object into the liquid (not touching the ground) and having a force gauge hold the string. Depending on specific gravity the force gauge reads different values.

Your weight does not touch the ground and you need to hold it with a string. A heavy object will not be affected by changes in the liquid voyancy which is what's being measured. Without the string it will sink. Once the object especific weight surpasses the espeific weight of the liquid it sinks. To do that the especific weights of the liquid and the object must be similar and that's exactly what they do with the gravity measuring bulbs when filling them with pellets of heavier metals. They are trying to match both to make the object float at a certain depth/ Soemting like subs. Please don't take me wrong we are just brainstorming here and we all learn from each other. That's all. Thanks  smiley-wink
213  Using Arduino / Project Guidance / Re: Taking a shot at specific gravity measurements on: February 01, 2013, 04:31:54 pm
I don't get it. How wil the liquid specific gavity will affect your weight? Oh the other hand if you are weighting the liquid why do you need the weight? I understand the liquid weight changes; but the weight pounds will change with the liquid specfic gravity.
Sorry, you are right I don't understand the method.
214  Using Arduino / Project Guidance / Re: Solenoid Artistic Function - Magnet and Glass Tube on: February 01, 2013, 04:21:34 pm
You did this before? Any proofs beyond your reasoning that it would work? What is the expression of magnetic force on a magnetic dipole?

I haven't mentioned specific quatities or anything.. It's just simple reasoning, You just need to look at solenoids woking to realize about that. The cores don't rotate.

And you? have you done that?. Do you have poof of that other than your reasoning? What's the equation for magnetic force depending on the distance and current? Did you calculated that? With what values because n0 one here has nmentioned anything like specific numbers for currents etc. This is just brainstorming.
215  Using Arduino / Project Guidance / Re: Solenoid Artistic Function - Magnet and Glass Tube on: February 01, 2013, 04:13:29 pm
Maybe the feedback siganl can be solved like this. Just maybe. Let' see what they find wrong with it and maybe we can improve it.

You can't touch the magnet with anything as it will affect the position and look awful; but..

You can place a round piece of reflecting something in top of the magnet thing. At the end of the tube you palce an LED and an LDR (light depending resistor) then you get the reflected light from the mirror and convert it to voltage with the LDR. The closer the magnet the more reflection you'll get and the higer the voltage. You will need to use infrared or something to avoid ambient light from affecting the thing.

Whatever you do with the magnet it has to move freely and you may need a hole in the middle or something to allow the air flow back and forth otherwise the piston efect it will create will slow it down or prevent it from moving altogether when the air gets compresssed. You can also vaccum the tube after done and seal it again as they did it the past with vaccum tubes. Vaccum tubes again? smiley-cry
216  Using Arduino / Project Guidance / Re: Solenoid Artistic Function - Magnet and Glass Tube on: February 01, 2013, 03:54:10 pm
Not sure if it will work. If you power the solenoid it will suck the magnet in to the middle if you power it the other way, it will try to turn the magnet, not really pushing it to an end.

I don't think so. When the coil polarity reverses the force will reverse as the magnet poles are still in the same position. The round tube will not allow the magnet to rotate to reverse its poles. Think about why swolenoids work. If the magnet and coil poles are opposite the thing will fly to the closest end as that will be the dominant attracting force and the closer it gets the stronger the force.\

The end breaking problem by the magnet when hit can be solved by using a small magnet covered in 2 layers of soft material on both flat sides.

The feedback signal for the control loop I'm still thinking on that one... smiley-grin
217  Using Arduino / Project Guidance / Re: Taking a shot at specific gravity measurements on: February 01, 2013, 03:27:08 pm
The bubbles issue I think is not a problem as they don't form constantly in a stream or something like that. On the other hand the liquid voyancy is not a rapid changing thing. It will take hours for the yeast to  do their business before it changes in a detectable way, therefore a bubble here and there will not affect the results I guess. If a bubble appears then you get a way off reading and you just need to way for a bit and take another reading. The soft can take care of that. A very slow changing parameter is being meassured therefore rapid changes will be noise and can be discarded.
218  Using Arduino / Project Guidance / Re: Taking a shot at specific gravity measurements on: February 01, 2013, 03:15:31 pm
I think the weight mass method you are proposing is good; but you will need to set a spring or something to make the thing retract when the weight goes up and calibrating that spring will be a difficult task. The floaters move freely. Floaters have been used forever to meassure liquids specific gravities and that maybe the reason why.
Anyway if the weight (which is acctually a floater too) can be attached to the weighting system without affecting the meassurement then maybe it is another solution to the same problem.
A basic rule in measurements is that the meassuring system used should not affect the system being measured.
219  Using Arduino / Project Guidance / Re: Taking a shot at specific gravity measurements on: February 01, 2013, 06:30:32 am
I have been thinking and maybe the surface level change problem can also be solved by using a differential method.

Let's say you use a second similar floating device with complete voyancy (floating at the surface of the liquid). If this second device is not affected by changes in the liquid voyancy then you can use it to measure just the surface level. Then by substracting the two signals the difference will be the difference in the voyancy of the liquid. To do that, both sensors outputs (after demodulation) can be fed to a differential amplifier ( easy to build, check the LM324 datasheet) and that will be your liquid voyancy signal to be send to Arduino analog input. That way you will not need to calibrate the system that much; but just at the beginning. I think you Project its completly doable that way.
220  Using Arduino / Project Guidance / Re: Taking a shot at specific gravity measurements on: January 31, 2013, 08:52:08 am
You don't need a Pr Sensor to find the position.
Maybe...
Let's say you place the bouy support (tube) on the container cap. Then the bouy can slide vertically through that tube depending on the liquid voyancy.Then you place a rod with a ferrite section in the bouy shaft and windings in the tube coincident with the center of the windings at normal voyancy. Study LVDT (Linear Variable Differential Transformer). You can convert any displacement of the bouy shaft to electrical signal at the output of the LVDT. You can make your own LVDT by winding a wire on the tube (2 windings). There are specifics on how to do that of course. You need to study that. The advantage is the bouy will be a passive element with no wires and the electrical system will be on the support attached to the container cap and all that can be external if you make the bouy shaft long enough.
To make the sensor make to identical windings on the tube. One for excitation where you apply a high frecuency low voltage signal (let's say 10 KHz). The other winding is the pick up coil where you receive the signal. When the rod (ferrite position changes) the amplitude of the picked up signal changes. Then you do AM demodulation to recover the envelope with a simple diode and a low pass filter (a capacitor). The envelope is your voltage changing with the rod position and therefore voyancy. If you want you can go FM by using the inductance as a component to change the frecuency of your oscillator (study Clapp Oscillator). The ferrite movement will affect the inductance of the coil and then you can demodulate the signal by using a phase detector (XOR gate) or a PLL unit like the CD4076. You need to study that too. It will give you a voltage output dpending on the frecuency changes. You can amplify (using LM324 if required) and feed that to Arduino. The FM version will be more complicated but you will get better inmunity to noise.

The main problem I see is you will have to be Zeroing the stuff regularly as the position of the bouy will change not only with voyancy; but with the liquid level inside as it evaporates, etc... maybe others have an idea of how to solve that problem. If they don't come up with a nice solution you may end up with an evaporation meter instead. smiley-mr-green
221  Using Arduino / General Electronics / Re: Small power source for one century on: January 30, 2013, 09:50:29 pm
It's a good project you build your clock; but...
Also build a freezing chamber and I'll volunteer to get frozen to see if your thing pops after 100 yeas or not smiley-grin . Don't use the device to tigger my ice melting in case it fails...
222  Using Arduino / General Electronics / Re: Small power source for one century on: January 30, 2013, 09:06:40 pm
I have been thinking in somekind of thermoelectric geneator for years that maybe can be used for this... There is a temp difference from the surface  down as you dig a hole. Maybe placing some bi-metal rods can havest some of the energy from the difference and it will be electrical energy already. If you go all CMOS and sleeping mode most of the time maybe you can use that energy to recharge something while sleeping or have two sets of batteies... Problem will be corrosion... but what if the rods are protected with vinyl or something like ceramic painting (like ovens)?. Maybe they produce enough power to supply the thing without a storage device. Remember spacecrafts use thermopiles (with a nuclear capsule for heating) to generate  electricity. You don't need that much energy so you don't need the reactor. Multiple rods in parallel and series (like batteies) may meet both voltage and current requierements even with small differences in temp. Maybe... Testing is the poblem.
I also think semiconductors should last that long specially because there will be negligible amounts of heat generated.
223  Using Arduino / Programming Questions / Re: Computer Serial Number on: January 27, 2013, 06:17:34 pm
That answer is for pure java.  Maybe someone here did something like that.
224  Using Arduino / Programming Questions / Re: Computer Serial Number on: January 27, 2013, 06:15:00 pm
Depends on how you look at it. I want it for my Arduino project. I want to read the computer sn from processing and match arduino to it. You can remove the post; but maybe others need the same solution.
225  Using Arduino / Programming Questions / Re: Computer Serial Number on: January 27, 2013, 06:09:10 pm
Anything that's unique to the computer and does not change.
Thanks.
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