Hi, my project is to build an 'aperture wheel', for a very precise known timing (29.9 Hz ||| 33.36702 ms ||| 1798 bpm)... name it a's you want! It's a pulsar, it have it's own atomic frequency. cf.: experiment similar to: https://www.messier.seds.org/more/m001_pulsar.html
To start on the good feet, what should I use for precise timing, 360deg Servo Motor or stepper motor, do I need to add an external retroaction from an encoder? Wich library would be appropriate to use, suggestion on the motor drive required specification, Sketch examples I may experiment and adapt to my specifics needs, etc.
I also want to display the RPM (or timing of any kind) on a display (because I may have to play with fine adjustment and I'll probably reuse this project for other pulsars, with a different frequency, of course!).
I'm all new to the Arduino universe, and my firsts try from Arduino's examples are giving me headhaches when I try to add, on my OLED display, the RMP value of the stepmotor, then the stepper got quite erratic. I also think that the use of buttons would be more precise then a potentiometer, but didn't try those implementation in my sketches yet.
Web search gave-me some interesting speed results, with some demonstrations sketch, by using timing instead of steps as library's.
I'll buy what is needed to have good results. Your advises and suggestions of all kind are all welcome.
¨-_-¨ Arduino, It's Hard We Know!!
Please read the topic "How to get the best from this forum".
How accurate does it need to be? Short & long term?
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If you are using a 9V battery like this.
Don't.
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Info about multi things
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I2C scanner
https://www.arduino.cc/reference/en/libraries/i2cscanner/
What did the I2C scanner report?
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Bread board power rail split
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Serial Input basics.
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The search box is a useful tool.
For instance using the words "9v battery" in the search box one could find lots of reasons why this may be a bad idea.
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disclaimer
The events portrayed in this post are not all true. The names are not real names of real people and real organizations.
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You can create very accurate timing using Arduino timers:
Of course, ALL timing is based on the external crystal used, so with the stock 16MHz crystal, the accuracy is based solely on the minimum pulse width.
29.97 Hz is related to 5034965 by an integer.
check here for other possibilities:
https://en.wikipedia.org/wiki/Crystal_oscillator_frequencies
The exposure time: 90 to 180 sec; Accuracy below 2% would be a good start.
I figure a wheel with 2 to 8 holes.
Still don't know if I'll use a DC motor, or stepper.
I thought you said ultra precise?
We'll have to perform some tests to know what precision it may reach/need, with the equipment I have access to; without overshooting in specs, stupidly.
Having the right equipment & mind-way from start, begin's, by asking to our contacts circles. There is almost no documentation on what we want to do: Long exposure of "almost" shuted-off pulsars.
^-_-^ For sure that: the more precise I get, the more my "almost" will be small...
Well, kinda... I think!
** Update: The operator (who once upon a time, was a DJ 
) tell me as follow:
Francais: La roulette va rouler a la meme frequence et essayer d'etre dephaser de 60, 120, 180, 240, 300 degrees. Il va y avoir beaucoup d'essai et d'erreur. Avec un orifice d'environ 3 cm de diametre, je vais prendre 1 a 2 minutes d'exposition a une frequence donner, puis ralentir la frequence un peu et revenir a la meme frequence, cela permettra d'etre decaller un peu. Reprendre des photos...
English: The wheel roll at the same frequency and try to be out of phase by 60, 120, 180, 240, 300 degrees. There is going to be a lot of trial and error. With an orifice about 3 cm in diameter, I will take 1 to 2 minutes of exposure at a given frequency, then slow down the frequency a little and return to the same frequency, this will allow me to be off the hook a little. Take pictures...
So, as he said: a DC motor and a simple encoder linked to the wheel would be the best? Use of buttons up/down could allow a more accurate offset than... a finger touch to the wheel!! But I technologically think that a stepper motor would be more precise, predictable and repetitive? I pain to evaluate the precision involved for each motors at 29.9Hz, at first.
Hi again, some peoples wanted more info on the project for better guidance and needed precision.
If you want to do some research, our first practice target is:
M1 Crab pulsar (PSR 0531+21, NP0532)
I don't master all the exact details, the project, it have been requested by an astronomer friend who have built it's own observatory.
Briefly, the nature of a pulsar is to flash light, like a stroboscope on a dance floor.... My friend want a wheel with holes in front of the CCD camera. The timing of the open hole will occur when the pulsar is at it's minimum luminosity (this is what I compare to the shutted light).
Doing so, it will be possible to stack expositions. Each exposition will be of a duration around 90 to 180 seconds. We'll perform some photography tests. From the results, an offset delay will be applied to adjust exposition timing on the pulsar period; followed by an other photography; etc. So frequence stability will have to be maintained for at least 15 to 30 min at first. The pulsar regularity is comparable to an atomic clock....
What will be seen and measured by my friend is confidential and way too complicated for an Arduino forum. If I resume I want to build an over 2000$ instrument for the price of a pair of running shoe.
The people on the forum only have to help me to master how to control, with precision, a motor.
^-_-^
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