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1  Using Arduino / Project Guidance / Any company/service that can print and assemble a circuit board for me? on: May 23, 2014, 03:00:51 pm
Hi all. I am looking for service than can manufacture a circuit board to my specifications and mail it to me, all soldered and ready to go, for a relatively low price margin. I need to put together a soldered circuit, and having this done professionally seems more feasible as the nearest hobby electronics store is more than 100 miles away. I am willing to pay more if absolutely required, but saving a few bucks is always nice. Is there any service that can do this?
2  Using Arduino / Project Guidance / Need help with Touche and Guino for Arduino (Capacitive sensing) on: May 16, 2014, 05:28:58 am
Hi all
I am trying to build the Touche for Arduino for my next project. I am following this instructable (The Guino library): http://www.instructables.com/id/Touche-for-Arduino-Advanced-touch-sensing/?ALLSTEPS

I built it, and it does detect touch, but only sort of. Instead of the clear graphs as in the instructable, I only get something like this: http://imgur.com/kmNYVmM

And while it does detect touch, it can't differentiate between the kinds of touches, unlike that in the instructable. Also, at some occasions, the graph is reduced to little more than a line. My question is: What could the problem be and how can I make this more sensitive? Thanks in advance
3  Using Arduino / Sensors / Re: Sweeping Frequency Capacitive Sensing? on: April 29, 2014, 10:49:38 pm
I went through the Arduino code and apparently it uses PWM to produce a range of frequecies one after the other (I guess this is where the "Sweeping Frequency" comes from.) Can anyone please explain the circuit to me? This looks a little like an LC filter, but what exactly is it doing here?
4  Using Arduino / Sensors / Re: Ideal sensor for comparing distances between points less than 15cm apart on: April 29, 2014, 10:31:56 pm
Quote
Ultrasonic sensors sound ideal for this project. One more question though: How much will the accuracy suffer if the medium of transmission of the waves is not air? For example, what if instead of pointing the emitter directly towards the sensor, I point it down at the surface?

No way. The ultrasonic sensors are based on sound reflection, not vibrations. So pointing the sensor to the ground will cause a 0 reading. You need to use either multiple sensors on the moving object , either one of every stationary point.Environment has its influence . Temperature,pressure and air humidity will affect the speed of sound and thus your measurements. But unless you are not using them in extreme changing conditions you should be fine (you can also make software compensation for temperature/air humidity(the sensors are cheap dirt).

Another option would be using a gyro/accelerometer/compass  combo. You don't need the stationary points, only sensors on the moving object. You will always get x,y,z difference between the actual position and the initial point . You can check the MPU- 9150 device., for example. I don't have experience with them so cannot tell you the price/precision.

Okay, thanks a lot smiley I am looking into it right now
5  Using Arduino / Sensors / Re: Do Sensor command only once on: April 29, 2014, 01:32:05 am
This should work:

Code:
int Motor1 = 2;
int Motor2 = 7;
int Pumpe = 10;
int Helligkeit;

void setup()
{
  pinMode(Motor1, OUTPUT);
  pinMode(Motor2, OUTPUT);
  Serial.begin(9600);
}

void loop()
{
  Helligkeit=analogRead(0);      
  Serial.println(analogRead(0));  
  
  if(Helligkeit<20)    
  {                              
    digitalWrite(Motor1, HIGH);  
    digitalWrite(Motor2, LOW);
    delay(500);
    digitalWrite(Motor1, LOW);  
    digitalWrite(Motor2, LOW);
    while(Helligkeit<20)
     {
      Helligkeit=analogRead(0);      
      Serial.println(analogRead(0));
     }
  }
  if(Helligkeit>20)                      
  {                              
    digitalWrite(Motor1, LOW);  
    digitalWrite(Motor2, HIGH);
    delay(500);
    digitalWrite(Motor1, LOW);  
    digitalWrite(Motor2, LOW);
    while(Helligkeit>20)
    {
      Helligkeit=analogRead(0);      
      Serial.println(analogRead(0));
    }
}
 
6  Using Arduino / Sensors / Sweeping Frequency Capacitive Sensing? on: April 29, 2014, 12:51:02 am
So I read this amazing instructable: http://www.instructables.com/id/Touche-for-Arduino-Advanced-touch-sensing/?ALLSTEPS

Apparently, this works by using "Sweeping Frequency Capacitive Sensing". What exactly is this SFCS and how does it work? Is its mechanism anything like RCtime? (where we measure an object's capacitance or resistance by charging/discharging an RC circuit and measuring the time it takes)
7  Using Arduino / Sensors / Re: Ideal sensor for comparing distances between points less than 15cm apart on: April 27, 2014, 10:33:56 am
I guess it depends on the definition on "accurate" and "small distances". From what I've seen/tested so far  ultrasonic sensors  have between 1-3 mm resolution in 20 mm - 1000 mm. This depends mostly on the transducers and how good is the software on the PIC/8051 on the module. Above 1000mm you can expect 2-5 mm. Bellow 20 mm , most of them cannot measure. The modules are cheap so you can test it yourself:

http://www.robot-electronics.co.uk/acatalog/Ultrasonic_Rangers.html 

Lasers have of course bigger resolution (0.1 - 2 mm) but they are more expensive, have low directivity   and higher power consumption.  If you want your project battery powered using lasers/LED...it can be tricky. Also, if you plan to use this setup outside or in place where sunlight is present then IR is not an option.

Ultrasonic sensors sound ideal for this project. One more question though: How much will the accuracy suffer if the medium of transmission of the waves is not air? For example, what if instead of pointing the emitter directly towards the sensor, I point it down at the surface?






Sound waves, instead of travelling directly through air, could travel through the surface (maybe like ripples in water). That would solve the problem of directivity.

I can conduct the experiment in a dark room, so IR won't be a problem either.
8  Using Arduino / Sensors / Re: Ideal sensor for comparing distances between points less than 15cm apart on: April 27, 2014, 09:48:47 am
OK I understand a bit more now. Do you mean you have two toothed gears that move against each other and a pen tip trapped somewhere between the gears and records the graphs? If you had paper under it, would you get the graphs? Spirographs are the resultant curves, not the objects that are rolling around each other. And you can solve it or make parametric plots of what happens, simplest being a wheel rolling on flat surface.

If you want to track the pen tip, why not using a capacitive touch surface and metallic pen tip for the sensing? It's better than 5mm accuracy. You can also use an active digitizer tablet and its pen and track it like tracking any mouse movement on computer using Processing. Why devising something while technology already exists? Any reasons the above two solutions would fail? Again I still don't have complete understanding of your situation.

Sorry for the confusion. I did mean the rolling toothed gears, and if I were to place a paper under it, I would get graphs. I intend to study the graphs generated by a combination of two such rolling-gear-apparatus-things.

Capcitive touch surface and digitizer tablets are great for both precision and accuracy, but they get really expensive as the size increases. My budget is of about $150, but since I am a college student, less project cost equates to more pizzas. Using IR LEDs or ultrasonic transducers would save me much more money.
9  Using Arduino / Sensors / Re: Ideal sensor for comparing distances between points less than 15cm apart on: April 26, 2014, 11:14:02 pm
What exactly are these references and the object? Without a description, I can't think of a generic method that works  regardless what they are. Do you have a picture of your set up?

Thanks for the reply. Here are some (crappy) MS Paint illustrations:
 


I want to study different combinations of two spirographs (at different speeds, angles etc.). There is a rectangular surface/region with a sensor/tracker (shown in red) at each of its corners. The two gray lines are rods that extend to the two different spirographs which we want to combine. The spirographs will move the rods, and hence their intersection (the target point), in a crazy but mathematical pattern. I want to track and study this point. Side view:

Top view:

Technically, I only need 2 sensors/trackers. If I use 4, I can average the results from each pair to get more accuracy. I hope this clarifies it.

If IR LEDs  and phototransistors had enough range and angle, I could use an LED (facing down) at the tracking point and phototransistor at the corners. If ultrasonic worked in small ranges (like 3-6 cm), I could stick an emitter/transducer to the tracking point, and sensors/transducers at the corners.
10  Using Arduino / Sensors / Re: Ideal sensor for comparing distances between points less than 15cm apart on: April 26, 2014, 05:58:22 pm
 
Laser Displacement sensor.

Thanks for the reply. Is it possible tro use a laser displavement sensor to track a moving object?
11  Using Arduino / Sensors / Re: Ideal sensor for comparing distances between points less than 15cm apart on: April 26, 2014, 06:16:57 am
IR seems like a decent option. I would use 2 LED on X pointing to A and B. Only 1 LED should be open at a time. You should get a strong beam on one fototransistor and a weak one on the other. After that you would need to experiment and implement your own algorithm. There are LED with high directivity ( usually dependent on the LED shape)

Another option would be using ultrasonic sensors. You use one transducer (can transmit and receive) on A and one on B. You transmit from A and listen to A and B. Do the same from B. Depending on the responses you can figure out the position. The ultrasonic sensors have 1 mm - 3mm resolution and the low frequency ones have high directivity. This won't work if the object X is very small/ sharp since ultrasonic waves  won't bounce. You should be able to do 10 measurements/s. You can can go higher only of there are no objects in nearby vicinity.


Thanks for the reply! The two-LED option will probably not work because X moves around a lot. Can I partially cover the outside of the LED with a reflective surface? Maybe that could redirect the light to spread equally in all directions. 



Using ultrasonic transducers seems like a brilliant idea. Maybe I can attach a transducer to X and let A and B recieve the signal from it. What will be the effective range of the ultrasonic transducers? I have read that they are not as accurate for small distances.
12  Using Arduino / Sensors / Re: Position detection in a room on: April 26, 2014, 04:21:07 am
Someone suggested me to use 2 Kinects at once. Each one is connected with one computer. Instead of fixing it on the ceiling, these are placed on the ground. One is from the front, and another is from the side.
Each one detects only X axe and Y axe, without Z axe (since Kinect does not allow to detect an accurate depth). The two computers communicate with ex. OSC, and the combination of data would be X, Y and Z for the real space.

It is only the idea, though. I know it is not the scope of Arduino Forum, but any ideas or any suggestions?

How about a normal webcam? We only need the position of the dancers' feet, so, instead of mounting the cameras at the ceiling, we only need to mount them high enough to see the whole stage (say 6 feet). The camera will probably see something like this:



- The viewing angle skews the rectangular stage into a parallelogram.
- We only need to concern ourselves with the dancers' feet (shown in green) and/or body center.
- Instead of tracking absolute distance, we can figure out the ratio of distances from different sides of the stage.
- We can track multiple dancers if needed.

If the camera is kept at 6 feet, it is likely that it will be unable to see the whole stage. In that case, some markers (shown in blue) can be used as references for distance/position. This way we can use multiple cameras to cover the stage. As a bonus, you also get a (crappy) recording of the dance!
13  Using Arduino / Sensors / Ideal sensor for comparing distances between points less than 15cm apart on: April 26, 2014, 02:47:18 am
TL;DR: IR LEDs and phototransistors are good only for a small range of angles and need to be pointed at each other to really work. I need something less 'directional' that can work in a range of 3-15cm while providing a rsolution of nearly 5mm or better.

Hi. I need to track the position of a moving point. For this, I plan to compare its distances from two stationary points and do some math to calculate its coordinates.



All I need are the ratios a/c and b/c. Here X is the target and A and B are the two stationary points. Point Y is another stationary point that acts as a reference for the distances. All the distances are very likely going to be between 3 cm and 15 cm.

I am currently considering IR LEDs and phototransistors. I can use the LED as the target X and the phototransistors as A and B. The LED will emit light which, depending on the distance, will vary in intensity. This will be picked up by the phototransistors. I can compare the readings in A and B to figure out the ratio. The problem is that they only work in a very small range of angles and pretty much need to be pointed at each other. This severely restricts the movement of target X. I need something less 'directional' (Maybe like a light bulb). Is IR a good idea at all? What sensor/arrangement would be ideal for it?
14  Using Arduino / General Electronics / Re: making a potentiometer with paper? on: April 13, 2013, 07:06:37 am
This means that you are unlikely to get a linear relationship between distance and resistance.

Thanks for the reply! My paper is actually pretty uneven smiley-lol .I guess the relationship won't be linear then. I might have to find another way to determine the distance then smiley-sweat . IR LEDs anyone? smiley-lol
15  Using Arduino / General Electronics / Re: making a potentiometer with paper? on: April 09, 2013, 05:02:05 pm
I tried plotting with yet another piece of paper. The total resistance was 29k this time. It had a grid printed on the back, so it was easier to divide into sections. There were 15 equidistant marks, with the ground at 0 and 5V at 14. I measured each mark 4 times, and plotted the average.The image shows the graph of the averages. The reading on mark 0 shows almost no variance, while it increases to ~45 on mark 4, then decreases to ~21 on mark 7, suddenly becomes 38 at mark 8, and again decreases, to ~13 on mark 13 and again,almost 0 on mark 14. Varience here is the difference between lowest and highest reading(more like the range of deviation). Sources of error could be, first, the Arduino itself; since it was reading about 200 even when there was nothing on. Also, I used alligator clips to hold the contacts in place, and they have pointy teeth which were digging into the paper. I am not sure if that could have actually affected the resistance much(there's smaller contact area),but still.... Also,the paper was not held perfectly straight. It kinda formed an arch while taking a few readings(about 4 marks?), so that could have affected the readings. But the readings were not very different in this case, so I guess it did not really make much difference. This is my first time doing anything like this, so I might suck at it. Please excuse my stupidity and thanks for the replies!  smiley
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