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i am currently working on my final year project for diploma in electrical and electronics engineering. the project that im working on is about a coin counting jar, which means when coin is inserted into the coin slot, a 16x2 LCD screen will display the value of the coin inserted and the sum of all the coins. at the same time, if an amusement park token or counterfeit coin is inserted, the machine is able to reject it. the PIC that i have selected is 18F4550 because it has been provided in PIC workshop before. however, the method to detect counterfeit coin is still unsure. i tried to use FSR (force sensitive resistor) but it is not sensitive enough. is there any other component, like a strain gauge or load cell or other alternatives that can measure grams, to get the weight of the coin? or other methods to detect counterfeit coins? please help me out!!
Would it work if you just analysed the charcateristics of the sound the coins make when they drop on to a hard surface? You might grab a piece of the sound then do a FFT on it. The frequency spectrum might turn out to be a pretty good "fingerprint".
But if someone kicked the coin box (with some coins in it) it would produce a true coin noise which could fool your detector.
... and some people could reproduce the tones to indicate that a payment had been made when in fact nothing had been paid.
Joe Engressia, a blind seven-year old boy. Engressia was skilled with perfect pitch, and discovered that whistling the fourth E above middle C (a frequency of 2600 Hz) would stop a dialed phone recording. Unaware of what he had done, Engressia called the phone company and asked why the recordings had stopped. This was the beginning of his love of exploring the telephone system.Other early phreaks, such as "Bill from New York", began to develop a rudimentary understanding of how phone networks worked. Bill discovered that a recorder he owned could also play the tone at 2600 Hz with the same effect. John Draper discovered through his friendship with Engressia that the free whistles given out in Cap'n Crunch cereal boxes also produced a 2600 Hz tone when blown (providing his nickname, "Captain Crunch"). This allowed control of phone systems that worked on single frequency (SF) controls. One could sound a long whistle to reset the line, followed by groups of whistles (a short tone for a "1", two for a "2", etc.) to dial numbers.