Money Detector by color recognition

[Nayyi]

guys i am again working on a money detector circuit. (was unable to make one in my first time...) i would like to use LED's of different colors and LDR's to detect reflected color. any idea how would i start?

 

[Hero999]

I don't know what kind of money you have in the Philippines but it wouldn't work for UK currency as we have many coins that are the same colour and it depends on whether they're clean, dirty or tarnished.

 

[House0Fwax]

Here's a method.
https://www.robotroom.com/ColorSensor.html
Robot Room - Cadmium-Sulfide Active Color Object Sensor

 

[Nayyi]

money denominations here are quite colorful, but i will be using 20, 50 and 100 orange, red and blue respectively. how will i be able to make the LDR to see the differences with these colors and direct the output to a set of LED indicators...?

 

[Hero999]

You could have a range of LDRs with different fillters and a white LED or just one LDR and illuminate the money with different coloured LEDs and monitor the resistance of the LDR. I would recommend the latter and LDRs are more expensive than LEDs and you can get RGB LEDs which will save space.

 

[blueroomelectronics]

Decent money detectors will us an inline ccd sensor (like old hand scanners) to scan the image, combined with other methods like UV to determine the bill and its value.
Colored paper would fool a simple color detector system.

 

[Brevor]

I worked in the currency validation industry for 20 years. The most modern banknote validators that are being used today use 3 colors of visible light
red green and blue, as well as 2 or 3 invisible infrared wavelenghts.
The way the process generally works is only 1 color is switched on at a time.
The reflected light level is sampled with phototransistors through an ADC to the microcontroller. As the bill travels through the validator it is scanned with each color several hundred times a second and the reflected light levels are stored in the microcontroller. When the scan is complete it has a graph stored in memory for each color. It then compares this to a library of bill signatures it has been programmed with. If it finds a close enough match the bill is accepted.