Coin recognition Project

[Jeswin]

Hi Duffy,
Thanks for your reply. My mentor did advise me earlier to use short multilayered coils and I presume this reduces the reluctance significanty; I decided to use single layer as I was unsure of the response from mulilayered coils with an increase in frequency (skin effect and capacitance between layers). I am not very sure about the frequency change: the frequency determined by the source frequency which is set manually (unless you were talking about an oscillator).

With single layered coils I did not see any significant change in amplitude or frequency when it was connected in series to a pull up resistor and powered by an AC source after trying various british coins.

 

[Jeswin]

Coils for metal detection

Hi,

I am doing a project called 'coin recognition'. One of my methods is to design a collpitt oscillator and pass the coin near the magnetic field of the inductor (or through the inductor and measure the frequency response. I understand that metal detectors have a relatively large coil.

But I am unsure about how big the coil should be for detecting coins. Does anybody know what size the coils are in a vending machine.

This is for Birtish coins. Thanks

 

[duffy]

How many different threads are you going to start on this?
Here are some diagrams for coils in an existing coin mech -
https://www.electro-tech-online.com/custompdfs/2012/02/195.pdf
https://www.electro-tech-online.com/custompdfs/2012/02/190.pdf
https://www.electro-tech-online.com/custompdfs/2012/02/193.pdf
https://www.electro-tech-online.com/custompdfs/2012/02/1168.pdf
https://www.electro-tech-online.com/custompdfs/2012/02/1166.pdf

 

[Brevor]

But I am unsure about how big the coil should be for detecting coins. Does anybody know what size the coils are in a vending machine.

The coils are about the same size as the coin diameter, just something close it does not have to be exact.

 

[davenn]

How many different threads are you going to start on this?
Duffy

agreed with Duffy ....
Jeswin for heavens sake and the sanity of all of us, stop creating so many threads on the same topic!!
you have us all jumping all over the place!!

Dave

Mod's any chance in merging the threads if possible like they do on other forums ??

 

[Jeswin]

Hi thanks for your replies,
I apologise for the inconvenience caused. Apparently I have a lot of questions about the project since there is not much info about 'coin recognition' on the internet apart from patents. I will try and post it on the same thread next time. Cheers for the drawing Duffy.

Your Threads are now Merged. Moderation. E

 

[duffy]

Thank you, eric.

If the coin lacks any significant amount of a ferrous metal, the induction technique won't work well, or at all depending.

No, the induction technique works fine on non-ferrous coins. I've explained it twice now, look at post #2 and #20. This is how modern coin mechs work, it's how metal detectors work.

 

[Jeswin]

Hi,
An update on my project. I researched the working principles for a proximity sensor - it works by detecting eddy current losses. I connected the coil in series with a pull up resistor. When i bought a CONDUCTIVE non magnetic coin near the direction of the magnetic field, there was a voltage drop across the coil. I am not very sure why this happens - I thought the resitance of the coil would increase thus 'increasing' the voltage drop across it.
Another method I thought of trying was to extract the phase between voltage and current and this will give me a measure of how much the impedance has changed.

Could someone lead me in the right track. Thanks

 

[duffy]

When i bought a CONDUCTIVE non magnetic coin near the direction of the magnetic field, there was a voltage drop across the coil. I am not very sure why this happens - I thought the resitance of the coil would increase thus 'increasing' the voltage drop across it. ... Could someone lead me in the right track. Thanks

Read the post directly over that one.

 

[Jeswin]

Hi duffy,

Thanks for your reply. I understand it better now. I justed connected the indutor to a series circuit rather than an oscillator. But I am not too sure why the amplitude reduces for a magnetic coin (1p and 2p British coins).

I will experiment with an oscillator and see what happens

Thanks again.

 

[Jeswin]

Hi, I am aware that conductive metals will change the resitance of the coil and magnetic material will change inductance. I would like to know if there was a way to measure the change in both of them separately.

Thanks

 

[BobStewart]

Hey Jeswin, Have you concidered using a 10GHz FPGA, These are really amazing devices like the fellow brevor suggested these could monitor the two single inductors and the airgap transformer a few flux capacitors as well at the same time on different channels, using some VHDL programming, which is similar to C-- at faster speeds than a simple microcontroller.

 

[duffy]

a few flux capacitors as well

Wait, what?

 

[DerStrom8]

a few flux capacitors as well

Wait, what?

Hahaha, I was wondering the same thing

 

[Brevor]

Hey Jeswin, Have you concidered using a 10GHz FPGA, These are really amazing devices like the fellow brevor suggested these could monitor the two single inductors and the airgap transformer a few flux capacitors as well at the same time on different channels, using some VHDL programming, which is similar to C-- at faster speeds than a simple microcontroller

Sure that will do it But the coin acceptors I worked with were designed back in the early 1980's and used an old Intel 8048 processor running at 6 Mhz.