what is the technique used in coin changer/selector/alidator

[Mohamed Slama]

what is the technique used in coin changer/selector/validator

Hi

i have read about coin identification , and found the best technique is :

tow coils placed in oscillator circuit , if the coin passed through the frequency will be changed , i have applied this technique for denominations of coins but there are 2 denominations have the same frequency .

is there parameters another with frequency such as amplitude of frequency - instead of length , thickness or weight ?


any one worked in this project .

the idea is shown in this video

https://www.youtube.com/watch?v=Q3mkLca3xno

 

[D.A.(Tony)Stewart]

Did you put the coils on either side of the slot or concentric on one side.?

I wonder if they measure vector impedance or just use magnetic properties to shift LC VCO.
Size and position of the coils are probably critical.

For Eddy Current metal flaw detection, we used vector impedance change with quadrature PLLs detecting the current in dual coils and ADC.

 

[Mohamed Slama]

SunnySkyguy thank u for your reply

yes , i have put the coils on either side of the slot and concentric , so that the coin pass through two coils .

when the coin pass through two coils i measure frequency vector (at variable time) .

after measuring frequency as a vector , compare it by standard vector that i have measured befor .

- - - Updated - - -

For Eddy Current metal flaw detection, we used vector impedance change with quadrature PLLs detecting the current in dual coils and ADC.

i cant under stand this sentence

 

[D.A.(Tony)Stewart]

When we used to measure flaws in continuous steel tubing, We excited dual coils and measured the difference in amplitude and phase (Current Vector) to find signature defects. Our sensitivity was 50ppm. Here you have the opposite trying to find the a metal signature going past air gap. Consider the quadrature vector impedance change with a fixed excitation frequency rather than the minor pull frequency of an induction tuned oscillator. Imagine the impedance change as a polar plot normalized to the center and the resulting signature beings a pattern that changes with metal type and size.

For it to be effected by non magnetic materials you need to measure Eddy currents. Thats why I drew on my experience.