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31  Using Arduino / Sensors / Re: how to tell variable reluctance sensor on: April 22, 2014, 10:57:25 am

 since I posted the above message  a friend of mine did some digging and found the Post where I must have gotten the diagram from all time ago.

 I had the diagram wrong anyway so if your interested  you should look at this post,157697.0.html

I also attached a correct version of the diagram \
The thing I didn't know about VR sensors is that they are passive, i.e. they done take any voltage in - they  produce a small voltage , I think its a sine wave +/- and the LM393 is used to amplify and turn into 0 or 1's

However , the question still stands, is there an easy way of determining if the sensor is a VR one?
In the above Link , user 'DC42' seems to have know how to tell but never actually mentions how .

 The VR probes I've used at the refinery I worked on were simple 2 wire devices that feed a comparator to give a digital square wave output at a frequency proportional to the speed and number of teeth that the probe was sensing. I believe the internal construction is a magnet with a coil around it, and as a gear tooth passes the sensor face it changes the field of coil causing a change in the sensor output voltage. The sensor output voltage looks like a quai-sinewave and it's voltage increases with increasing gear speed, however once the voltage is above a certain minimum value the comparator doesn't care as it's just switching at zero crossings of the probe's output voltage.

32  Using Arduino / Motors, Mechanics, and Power / Re: Project a solenoid on: April 22, 2014, 10:43:54 am
Another question, how fast is current to fully power solenoid? 30-50ms or it's comprensive of stroke movement?

 It's a function of the induction value of the solenoid coil. Recall the old ELI the ICE man rule, (voltage E leads current I in an inductive reactive circuit, current I leads voltage E in a capacitance reactive circuit), so the higher the inductive value the 'slower' the coil is to respond. But this time probably pails in the 'speed' on having to move the mass of the plunger assembly.

33  Using Arduino / Motors, Mechanics, and Power / Re: Servos were trembling, especially when reaching 100% PWM duty cycle on: April 21, 2014, 03:14:52 pm
Could be a conflict on internal timers used depending on what pins you are using for the servos and pwm fans. Again from the reference:

The Servo library supports up to 12 motors on most Arduino boards and 48 on the Arduino Mega. On boards other than the Mega, use of the library disables analogWrite() (PWM) functionality on pins 9 and 10, whether or not there is a Servo on those pins. On the Mega, up to 12 servos can be used without interfering with PWM functionality; use of 12 to 23 motors will disable PWM on pins 11 and 12.
34  Using Arduino / Programming Questions / Re: PID not fully functioning on: April 21, 2014, 02:55:58 pm
The PID library has commands to set output limits both low and high for that kind of situation, it effectively clamps the output value between two values you set. You shouldn't try or have to do it in your code for every output command you process.

35  Using Arduino / Motors, Mechanics, and Power / Re: Servos were trembling, especially when reaching 100% PWM duty cycle on: April 21, 2014, 02:52:31 pm
You don't 'talk' to servos with analogWrite() commands. You include the servo library and use servo write commands as in the
following example.
#include <Servo.h>

Servo myservo;

void setup()
  myservo.write(90);  // set servo to mid-point

void loop() {}

More info can be found here:
36  Using Arduino / Storage / Re: What happens when a SD card full on: April 21, 2014, 02:03:29 pm
You are right fat16lib, i didn't remember that, physical storage in computers usually come labeled in Gibibit and not Gigabit
Also fat16 formating type, have a limitation of storage per file which i believe is 4GB, so OP you need to make sure that when the file is 4GB you create a new one

Never seen either used, did you mean Gigabytes?
37  Using Arduino / Installation & Troubleshooting / Re: What type of Arduino do I have? on: April 21, 2014, 01:59:24 pm
If you are indeed using a 4-wire FTDI cable then uploads will fail for lack of the DTR/RTS auto-reset feature and you will have to master the 'well timed manual reset' to be able to perform the IDE upload function.

38  General Category / General Discussion / Re: Good practices (Arduino Programming) on: April 21, 2014, 01:56:12 pm
Pass the popcorn, some of the things you have suggested I've seen argued between even experienced programmers, and fall into the catogory of 'personal preferences'. At least that is the impression I've gotten from hanging around here for several years.  smiley-wink
39  Products / The Arduino Starter Kit / Re: Problem with DigitalReadSerial on: April 21, 2014, 12:04:50 pm
Sounds like you two are describing two different symptoms/problems. One is only serial printing zeros the first saying "not response". The first points to a wiring problem or a broken input pin, the second a serial comm problem. Of course the sketch compiles with no errors so the program is not to blame.

40  Using Arduino / Project Guidance / Re: Addressing analog pins on the arduino pro mini on: April 21, 2014, 11:54:36 am
You might just have a bad analog pin. Note that the signal has a pull-up resistor to 3.3vdc at the mosfet, so the signal line will be a high is the pin is open circuit internally in the chip. Have you tried your 3 second test sketch on some of the other analog pins?

41  Using Arduino / Networking, Protocols, and Devices / Re: Arduino Mega I2C without USB - problem on: April 21, 2014, 11:35:01 am
If you are connecting 5.3vdc via the external power or Vin pin then you are using too low a voltage. From the product specs:

The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.
42  Using Arduino / Microcontrollers / Re: ATmega644p reboots on serial input on: April 21, 2014, 09:37:18 am
Was there some discussion a while back about issues caused by the proximity of the RXD0 pin and the XTAL1 pin? Was there anything to that? If so, was a solution found? (Not to take anything away from Crossroads' reply -- all good points there.)

Yes it was a real repeatable problem for some, but it was sensitive to board layout as clock and serial pins are in close proximity in the 644 and 1284 dip packages. Some board layouts had the problem, others did not. First fix was a R/C filter on the rec pin which helped most seeing the problem but not all. Finally someone suggested changing the fuse bytes to full swing clock and that seemed to help anyone having the symptom. So in my 644/1284 boards I use full swing clock even though I've never seen the problem as Bob's board layout seemed to not bring out the symptom because of good board/trace layout.

 I would try that 'fix', before blaming 3.3 Vs 5.0 voltage as I don't think anyone has demonstrated that causing a problem in a real world example, conservative datasheet specs recommendation aside.
43  Using Arduino / Microcontrollers / Re: Revive dead Arduino Nano on: April 21, 2014, 08:55:25 am
The new board description was for Nano with Optiboot. There is an Optiboot loader for the Nano in the archive which I used in one of my attempts. But to use this variant I'd need to add a different board type as this is obviously nothing official.

It doesn't matter which ATmega328 bootloader I choose. Flashing with USBasp makes the board work (while being attached to USBasp). If I remove USBasp and plug in the Nano the usual way, it plays dead. You can see that very easy when using a blink sample: Freshly flashed, it blinks; plugged in the usual way only power LED is on.

 But the standard Uno optiboot loader works fine in the nano, no need to install from any other version, that was my point.

 Sounds like a defective USB FTDI serial interface chip. Does the PC see and 'ding' when plugged into the PC? If not it's defective,  if it does then perform the serial loop back test (there is a sticky around here somewhere) to see if serial data is possible.

44  Using Arduino / Programming Questions / Re: Scaling analog readings to stable values on: April 20, 2014, 08:48:55 pm

I am trying to scale my analog readings and I get into a problem of 'unstable' values.
My goal is to scale 0-1023 to 50-250. I am using the map function – map(A0, 0, 1023, 50, 250). I have set up a display to check the values.

The problem is that sometimes I run into 'middle' values, where the display is flickering between two – for example 69 and 70.
How would you approach this topic? Some DSP low-pass filtering?

Thanks for any help!

 Usual first method is to try to take multipule samples and divide by the number of samples taken, thus getting a average value. That acts like a first order low pass filter. Start with maybe 8 samples, divide by 8 then perform your map function. If that settles down the value you can then try with just 4 samples, etc.


45  Using Arduino / Microcontrollers / Re: Need clarification on the parameters of analogWrite(pin,value) on: April 20, 2014, 07:51:03 pm
Ok.. The 255 steps from the fact that 0 counts as one of the allowed values which total to 256?

And.. is this correct that each step is 2.55%  ,  or do you mean  100%/255 steps =0.392%/step
What about the frequency?  It is lock at 980 Hertz..  And there are a lot of instruction going on in the microcontroller. Therefore, isn't a 1 step just getting too close to the device clocking limits?
The analogWrite function is utilizing one of the three internal hardware timers in the AVR 328P chip, so once a duty cycle value is sent to the function the actual PWM is all done continuously and independently of the program, so no real effect on the rest of program performance.
Sorry about the line of questionings.  But I am building an optical device engine 100% with Arduino. It need a lot of precision and will like to understand that the realistic limitations are between the memory latency , speed and instruction.

Thank you all guys for putting up with me.
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