Simple Counterfeit Money Detector Circuit

A counterfeit money detector circuit is like a high tech flashlight that helps you spot fake bills.

It uses different types of light and sensors to check for special features hidden on real money.

It shines a special ultraviolet UV light to reveal secret markings you cannot see normally.

It has magnetic sensors to feel for hidden magnetic ink that is hard to copy in fake bills.

And it can even use infrared IR sensors to look for specific patterns or marks that are unique to real money.

If the detector does not find these special features, it might be a fake bill!

But remember, these circuits are helpers and not perfect so it is always good to be careful and check your money closely too.

Circuit Working:

Parts List:

Detecting counterfeit bills or money is crucial in todays world where advanced printers and sophisticated criminals are common.

Modern bill counters come equipped with features for detecting counterfeit money such as scanning for ultraviolet UV and magnetic MG properties.

These counters can process hundreds of bills per minute scanning each bill for magnetic properties as it passes through the machine.

This method is one of the fastest ways to identify counterfeit bills.

This article focuses on creating a DIY counterfeit bill or money detector using a portable ultraviolet lamp.

Instead of using a UV or Black tube, which is fragile and expensive this detector uses a group of ultraviolet light emitting diodes UV LEDs for the light source ensuring compactness and reliability.

The system consists of the UV light source and its driver circuit with the UV LEDs mounted in a transparent tube or on a small rectangular PCB for customization.

The UV LEDs require about 3.6V to operate so a step up switching driver circuit is used to provide a constant current to the LEDs.

The circuit is based on the LT1937 chip from Linear technology specifically designed to drive white LEDs with a constant current.

In this case the LT1937 is used to drive the UV LED string from a minimum of 3V DC supply input.

The LT1937 switches at 1.2MHz requiring only small external components.

The prototype uses the LT1937ES5 LYTN ThinSOT TSOT package.

The current through the LEDs is limited to around 20mA by a 4.7Ω 1% resistor R2.

To extend the life of the on or off switch S1 a 100k resistor R1 is connected to the ICs shutdown SHDN pin.

Capacitor C1 2u2 6.3V is used to decouple the circuit supply voltage to prevent instability caused by ripple and noise.

Formulas:

The DC/DC converter integrated circuit LT1937 is operated by a number of important formula and equations, most of which are connected to its switching regulator capability.

The following are some essential LT1937 formulae and factors to take into account:

Vout output voltage calculation:

The reference voltage Vref and resistor divider ratio attached to the feedback pin FB of the LT1937 define the output voltage Vout.

The formula provides an approximation of the output voltage:

V_out​ = V_ref​ (1+R_top​​ / R_bot​)

where,

• The resistor from the FB pin to Vout is called Rtop.
• While the resistor from the FB pin to ground is called Rbot.
• The value of Vref, internal reference voltage of the IC, is usually around 0.8V.

Frequency of Switching (f):

An extra resistor Rt wired from the RT/CLK pin to ground can be used to change the LT1937s switching frequency.

The estimated frequency is provided by:

f = 1600​ / R_t​

where,

• Rt​ is in ohms.

Selecting an Inductor:

The inductors L value has an impact on the converters efficiency and output voltage ripple.

It is possible to estimate the minimal inductance using:

L_min​ ≥ ​(V_in​−V_out​)* V_out ​* (V_in​−V_out​)​ / 8* f * I_out

where,

• When the input voltage is represented by Vin
• The output voltage is known Vout
• The switching frequency is represented by f
• And the output current is represented by Iout.

Peak Current of Inductor Ipk:

One may compute the peak current flowing through the inductor by:

I_pk​ = I_out​(1+V_out / V_in​​​)

here,

• It helps in choosing an inductor that can sustain the highest current level without experiencing saturation.

Efficiency η:

Among the many issues affecting the LT1937 converters efficiency are switching losses, conduction losses, and voltage drops.

One may evaluate the efficiency by using:

η = ​P_out​​ / P_in × 100%

where,

• Pin represents the input power and
• Pout represents the output power.

Note:

When creating and refining a DC/DC converter circuit with the LT1937, these formula are essential.

They aid in figuring out the values of various components, including capacitors, resistors, and inductors, to provide the required output voltage, switching frequency, efficiency and general performance.

For particular application circuits and comprehensive information, always consult the LT1937 datasheet from Linear Technology (now part of Analog Devices).

How to Build:

To build a Simple Counterfeit Money Detector Circuit follow the below mentioned steps:

Connect the components:

• Follow this schematic to connect the components:

Mount the UV LEDs:

• Mount the four 5mm UV LEDs LED1to LED4 in a small transparent tube or on a small rectangular PCB according to your preference.

Prepare the LT1937 chip:

• Ensure the LT1937 chip is in the ThinSOT TSOT package LT1937ES5 LYTN for the prototype.

Power the circuit:

• Power the circuit with a minimum of 3V DC.

Testing:

• Test the detector by placing a suspected counterfeit bill under the UV LEDs.
• The UV light should illuminate, indicating that the bill is genuine.

Adjustments:

• If necessary, adjust the position of the UV LEDs or the intensity of the light to improve detection.

Encase the system:

• Once you are satisfied with the performance encase the system to protect it and make it portable.

Final testing:

• Perform a final test to ensure the detector is functioning correctly.

Note:

• Exercise caution when working with UV light.
• Avoid direct exposure to skin and eyes.

Conclusion:

A counterfeit money detector circuit is an essential tool that uses various technologies such as UV light, magnetic sensors and IR sensors to detect security features present in genuine currency.

It plays a crucial role in preventing the acceptance of counterfeit bills and ensuring the integrity of financial transactions.

References:

Design of Counterfeit: Currency Detector

Datasheet IC LT1937