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46  Topics / Science and Measurement / Re: Create Your own Arduino Oscilloscope on: April 28, 2014, 08:08:04 am
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i don't see any link smiley
Starting at 00:14.
47  International / Proyectos / Re: Ayuda para proyecto con Solenoides. on: April 25, 2014, 11:45:25 am
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Si dispones de fuentes de alimentacion de PC en teoria puedes conectar varias en paralelo para conseguir la intensidad necesaria.
En teoria es possible; pero en la practica no es una buena solucion. Si las salidas son reguladas y los voltajes ligeramente diferentes se producen corrientes parasitas para igualar los voltajes al conectarse en paralelo.

Si no necesitas que todas las solenoids se activen simultaneamente entonces los requerimientos de la fuente en cuanto a corriente son mucho menores y siguiendo el ejemplo anterior puedes calcularla. En ese caso solo una solenoid a la vez) dada la abundancia de este tipo de Fuentes, puedes utilizer una ATX de computadora que de 1A de salida en los 12V.

48  International / Proyectos / Re: Ayuda para proyecto con Solenoides. on: April 23, 2014, 10:21:05 pm
Las 10 solenoides pueden ser activadas a la vez en alguna circunstancia? Te pregunto porque tengo entendido que no es muy facil conseguir una fuente de 12V 5A. Si ese es el caso, entonces la fuente debe ser capaz de entregar al menos un 20% mas de corriente que la maxima posible que demandara la carga para evitar que se sobrecaliente. En tu caso, entonces seria 6A y no 5A. Eso es sino anades algo mas como carga a los 12V. Eso hace que la fuente sea de 12V*6A=75 watts al menos. Pienso que no es muy facil  encontrar una fuente asi. No recuerdo bien; pero no creo que las Fuentes ATX de computadoras sean capaces de entregar tanta corriente en la salida de 12V. Si no es como pienso, entonces son muy buena opcion para tu proyecto, pues tanbiem entergan los 5V que necesitas.
49  Topics / Science and Measurement / Re: Volume Meassurement (Dry Method) on: April 23, 2014, 10:14:24 am
I started this Project because while working on the one below, I thought it was a good way to find out how many Gauges the operator had placed in the bench for real. This was perfect, as there was no need to add any extra hardware and only coding could solve the problem using the already installed hardware. I was seriously defeated at that time given the complexity of the whole thing, despite trying really hard for about a month and decided to tackle the problem in complete isolation from any other Project to better understand and study what was really going on.
I'm planning on posting a video with the rest of this project some day.

https://www.youtube.com/watch?v=HoorVivjawE
50  Topics / Science and Measurement / Re: Volume Meassurement (Dry Method) on: April 23, 2014, 10:04:36 am
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this could explain the spike (air is hot at the end of inflation in the bottle) and when you stop it is cooling and the pressure decrease ...
the slight difference between the deflation too (strong deflation at the begining causing a drop of the temperature ...)

Interesting explanation and very possible. Thanks

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Have you thought about differential methods or using acoustic resonance to probe
volume (the elastic constant of a container of gas depends on the volume of gas).

Thanks for the interesting links.
In practice, there are many different methods to solve the same problem. I had the intention to test this one, which by the way, I haven't found in use or tested anywhere else. Another alternative I think. Like any other, probably with some advantages as well as disadvantages.
51  Topics / Science and Measurement / Re: Functions Generator on: April 23, 2014, 08:40:48 am
Sorry, no its is not open source.
52  Topics / Science and Measurement / Re: Volume Meassurement (Dry Method) on: April 23, 2014, 08:05:41 am
Referring to the operation I can't find a convincing explanation for these 2 facts:

-The spike in the curve right when inflation finishes.
-The slight difference during the first half of deflation between the ideal exponential decay curve (pink) and the real pressure measured (top of the blue area). After that they are almost identical.

These are factors I've been weighing in to find answers:

-I'm using elastic (very flexible) silicone tubing which expands and contracts.
-Leaks in the system dependent on pressure, adding weight to the exponential decay at the beginning of deflation when the pressure is higher.
-The fact that air is a compressible fluid.
-Reduction in hose diameter to connect to the Pr. sensor.
-Delays in the transmission of the pressure waves inside the pneumatic system.
-Minute decreases in air temp as it enters the container and expands.
-The fact that I'm using a one piston compressor directly driving the pressure in the system and not from a stable pressure source such as a tank and inflating though a solenoid valve openning .
-The whole theory is wrong and I made too many approximations and assumed too many equivalences.

Even when these 2 facts appear to be constant and therefore systematic and the way I'm calculating the volume apparently effectively cancels them, it will be good to find answers to these questions.
Any ideas??
Thanks

53  International / Proyectos / Medicion de Volumen (Metodo Seco) on: April 22, 2014, 07:14:25 pm
He estado trabajando en este Proyecto por un buen tempo ya y ha sido mi "Proyecto Fenix". Habiendo sido derrotado en innumerables ocasiones por el mismo, he tenido que levantarme de mis cenizas con nuevas ideas y lecciones aprendidas. Aun cuando todavia hay que hacer ajustes en el mismo, al final pienso, la perseverancia triunfo. El objetivo era disponer de una alternativa al metodo de inmersion que ha estado es uso por milenios para medir el volumen de objetos irregulares, muchos de los cuales no pueden sumergirse en agua u otros liquidos. El obstaculo mayor fue encontrar/fabricar un envase que no tuviera fugas al ser presurizado. Trate mas de 10 diferentes envases y el mostrado es el que me dio los mejores resultados; pero es algo en lo que aun tengo que trabajar. esto es solo un prototipo para probar el concepto. El problema principal radica en que al abrir y cerrar el envase para introducir la muestra, las fugas por la tapa cambian y esto introduce un grado de incertidumbre inaceptable en los resultados.
El sistema puede ser extendido para medir las fugas de cualquier contenedor sellado.
Criticas, comentarios, sugerencias, ideas, opinions son todas bienvenidas.
Construido con Processing 1.5.1 y Arduino UNO
Gracias.
54  Topics / Science and Measurement / Volume Meassurement (Dry Method) on: April 22, 2014, 04:22:36 pm
Hi:
I have been working on this project on and off for a long time. It has been my "Phoenix Project". Being defeated several times by it, I had to come back from my ashes with new ideas and lessons learnt. Although still needs some fine tuning, I think perseverance prevailed. The goal was to have an alternative to the thousands of years old immersion method to measure the volume of irregular objects, some of which can't be immersed. By extension, the system can be used to measure leaks in a sealed a container. The greatest obstacle was finding/fabricating a leak free container under pressure. I have tried about 10 different ones and all of them leak. I still have to work on that.
I would like to hear your suggestions, comments, ideas, critics and opinions.
Thanks.

Project built with Processing 1.5.1 and Arduino UNO.
55  International / Proyectos / Generador de Funciones on: April 20, 2014, 12:29:19 am
Este es un generador de funciones para ser utilizado en el control de variables fisicas.

https://www.youtube.com/watch?v=0MGW8DekE10
56  Topics / Science and Measurement / Functions Generator on: April 19, 2014, 11:37:32 pm
This is a Functions Generator to be used to drive physical variables either directly by voltage variations using PWM or by means of a control loop implemented in the Arduino code. The latter will require using the corresponding sensors and actuators for the variable in question. At this time 12 different waveforms are available. Implementing the graphical representation and adjustments of the mathematical equations has been the hardest part in this project. Particularly difficult for me was implementing the triangular waveform even when it looks very simple  smiley-roll-blue. It took me a bit more than 2 weeks to build this Project despite the fact that I had most of the virtual instrumentation already built  At this time PWM is the only type of modulation available. The GUI includes buttons for Freq and Phase Modulation; but they are not active at this time. The Arduino code to handle these types of modulation is pending and honestly I have no plans to do it for now. The video shows a light bulb used as the load to observe the voltage variations from the PWM signal generated by Arduino. analogWrite(); is being used to generate the PWM driver signal through pin 3. A potentiometer connected as a voltage divider to analog input A1 is used to simulate the sample signal. "Full duplex" communication is established between the computer (Processing) and Arduino. It receives the values to drive the PWM signal and sends back to the computer the voltage sampled at analog input A1. This is the first time I implement "full duplex" communication involving data in both directions although high resolution is only one way. High resolution PWM is pending. All data collected while recording is logged as usual into an Excel file which can be viewed at the end of the video.
Built with Processing 1.5.1 and Arduino UNO.
Critics, comments suggestions, ideas, opinions, thoughts are all welcome.
Thanks.
http://youtu.be/0MGW8DekE10

57  Topics / Science and Measurement / Re: i need disolved oxygen sensor interface circuit on: April 16, 2014, 06:24:52 pm
Thanks for the link. I can't find a datasheet in the link provided or elsewhere for that particular sensor. In order to design an interface circuit its imperative to know what it gives at the output, bias supply, freq response, transfer function with respect to the O2 concentration, output impedance, etc. If you find the datasheet or any of that info please post here. I have no idea what are those parameters for that sensor neither if it is digital or analog. Request the datasheet from the supplier, they maybe able to provide it.
58  Topics / Science and Measurement / Re: i need disolved oxygen sensor interface circuit on: April 15, 2014, 08:02:02 pm
What sensor are you intending to use?. If you don't mention what sensor is it, we can't help you. At least provide a link to where we can find information about it.
59  Topics / Science and Measurement / Re: voltage divider for temp sensor on: April 07, 2014, 10:19:20 am
This is why you need a bias resistor and how to calculate it.
CAUTION: This method will give you a highly nonlinear voltage output with temperature, because of both, the thermistor is a nonlinear device for which its resistance changes nonlinearly with temp and because of the voltage divider used for bias. If you don't know the transfer function of the thermistor with temperature you will be in deep trouble to read the temp and making the linearization. I suggest you use a device giving an already linear output with temp like the LM35 for instance.
Good luck.
60  International / Proyectos / Re: Lectura pin digital defectuosa on: March 26, 2014, 09:27:27 pm
1-Pull up resistor ~ 1KOhm to 5V, switch to ground.
2-Rebote de los contactos (Bouncing). Puedes tartar de eliminarlo con:
-delay()
-Utilizando banderas como aqui: http://forum.arduino.cc/index.php?topic=222479.0
Quizas eso te ayude
Suerte.
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