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Topic: Wondering if this would work as a sensor (Read 1 time) previous topic - next topic

thomas3120

Jul 13, 2016, 12:52 am Last Edit: Jul 13, 2016, 12:53 am by thomas3120
Hello,
Attempting to use a real pinball ball launcher/plunger for playing virtual pinball on my arcade cabinet.

Some people I believe are using (CCD?) to capture images of the position (of the tip of the ball launcher) to get analog data.

I thought of something along these lines to get the analog data of the positions of the tip/rod- ball launcher.



Would this work?
Any suggestions or help much appreciated.

thomas

raschemmel

What ?
No inductance information ?
Do you have ANY test equipment ?

Magician

Hall sensors is much easier to attach.

thomas3120

#3
Jul 13, 2016, 02:03 am Last Edit: Jul 13, 2016, 02:09 am by thomas3120
What ?
No inductance information ?
Do you have ANY test equipment ?
I have a decent fluke DMM & Oscilloscope.  When it comes to electronics, Inductance has always been my weak point.

Just wondering if, in theory, this would work.  I was going to try different gauge coil wire and number of turns, etc...  BTW, would this produce any RF interference or other interference/side effects?

I may try Hall sensors as Magician said in his reply.

t


raschemmel

Air core inductors are ineffective. It probably won't work.


raschemmel

LVDTs are classified as "exotic" components , normally found only in professional industrial equipment and rarely seen in hobbyist level projects , although there is no reason why it couldn't be. (I am not familiar with prices)

thomas3120

#8
Jul 13, 2016, 12:41 pm Last Edit: Jul 13, 2016, 12:48 pm by thomas3120
Air core inductors are ineffective. It probably won't work.
So for optimal results, you need to have something like a solid ferrite core that's wrapped in the coil wire?



Also, was wondering if using a slide potentiometer which is install and working correctly, will there be any delay from aquiring values from the pot to the pinball software?


Another option I forgot to mention was some people use the middle mouse wheel.  Guessing there's a bit of hacking involved here...

One very last question...
A friend gave me one of those iRobot Roomba Vacuuming Robot.
Batteries are toast, so I salvaged all the sensors on it.  There's prob. some kind of Ping and or ir sensor...but any other ones I could use or try for this project?

Thanks again for the help/input,

thomas

raschemmel

All the magnetic component design at my job was done by a PhD magneteics engineer using a circuit simulator that told him the magnetic properties of the core material. We have kits of cores in plastic trays and we would make inductors by winding the cores and measuring the inductance on a $5000 LCR meter.
I only made the large inductors. Someone else made the small ones.

MarkT

The induced voltage is fairly easy to calculate if you know the geometry, strength of
magnetic field and number of turns.  You'll be able to determine a sensible number of turns.

Use two narrow windings, each the same, then you can measure velocity of the magnet.  Spread out
windings are not going to help.

Induced voltage is the rate of change of magnetic flux linking the coil, ie field-strength x area x N-turns / time.

A 0.1T field with area 5 cm^2 and 1000 turns, passing the coil in 0.01 second gives 5V
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

MrMark

Are you trying to measure the (starting) position of the plunger or are you trying to measure it velocity (or energy pulse) once it is released?

In your proposed setup, the position of the plunger should be proportional to amount of metal rod inserted inside the windings.  Thus you should be able to get starting position by building an inductance meter around your sensor setup.  The magnet and the uneven windings aren't needed if this is the goal.

To get something proportional to the energy pulse (energy imparted on the pinball), my first thought would be to integrate the induced current on your coil.  You might be able to do this simply by integrating (in software) successive voltage measurements across a suitably sized resistor.  I don't think uneven windings are necessary for this approach either.

MarkT

The current in the coil isn't really relevant, its the voltage that depends on the flux-change, you don't need
a resistor to measure a voltage.  The voltage integral will be constant as its dependent only on the total flux
change linking the coil, the _amplitude_ of the voltage pulse depends directly on the speed, and energy depends
on square of speed.   Using two coils allows timing of the passage of the ball, gives speed directly in measurable
units if you know the coil spacing.
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

raschemmel

#13
Jul 13, 2016, 04:23 pm Last Edit: Jul 13, 2016, 04:25 pm by raschemmel
IMO , the flux density is a function of the core, which is why air core yields such a weak flux density.
We have no information on the "magnet" such as it is so it is not really possible to treat that as a "core".
I'm sure if you have enough turns you will get some voltage but how you came to the value you did base on absolutely no information on the core is a mystery.


Quote
Using two coils allows timing of the passage of the ball, gives speed directly in measurable
units if you know the coil spacing.
I thought this was a "virtual" device and there was no physical ball.

polymorph

What are you measuring? Is that one winding?

You could have a coil with a lot of turns, with a magnet on the end of the ball launcher. Shottky diode rectifiers on the coil. The peak voltage generated will be a function of how fast the magnet moves through the coil, giving you a reading on how hard the launcher was hit.

You will need some protection diodes and a resistor between the output of the bridge rectifier and the Arduino to protect it.
Steve Greenfield AE7HD
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