Coin Identifier using Frequency Based System

Hello Every1,

This question is about a coin identifier system. Luking for ur quick replies as well. Im using transformer feedback oscillator to recognize the coin, based on the frequency variation of it. Now the problem is, I need a method to capture the frequency change when the coin is applied. Coin cannot stay for a long time through the coil.(1 second ) One has suggested to use PIC capture module for it. What is the best way to achieve the goal ???

Any suggestion, ideas and helps would be greatly appreciated.....

Thanx all

Have you researched the method which is used in metal detectors? It uses two air-core inductors in an oscillating circuit.

If any metal or substance comes close, it alters the flux field, changing the oscillating frequency.

The coin should probably roll past the coils. Sliding the coin may be problematic.

The coin should travel as close as possible to the coils. There should not be any metal intervening. There should be minimal metal in close proximity.

The coils must be sufficiently wide so that the coin is in front of them for a long enough time so that you can get a correct frequency reading.

You will need to test genuine coins and fake coins, and compile a list of all valid frequencies.

This reply assumes your coin already dropped into a valid column based on weight-versus-diameter.

Referring to the original question, I think that input capture is basically a good idea, provided the oscillator frequency is high enough to give sufficient relative resolution in a limited measurement interval, e.g. 50 ms. You'll possibly want to synchronize the measurement with a light barrier or other presence detector. Then take multiple frequency samples.