LED Voltage-Responsive Circuit Design

To create a circuit where five different colored LED change their illumination based on a voltage input ranging from 1.5V to 2.5V, we can design a circuit using a voltage divider, comparators, and LED. The idea is to divide the voltage range into five segments, each triggering a different LED. This explanation was taken from GORK
Any AI program can be used

Design Concept
• Input Voltage Range: 1.5V to 2.5V. This is the power sent from our patented sensor and I need the LED to light with a voltage change
• Number of LED can vary between 4-6 The sensor measure the contents of a LPG container. The voltage of the sensor changes with volume of LPG
• Operation: Each LED lights up in a specific voltage sub-range within 1.5V to 2.5V. The 1V range (2.5V - 1.5V) is divided into five equal segments of approximately 0.2V each this can vary if required
o Red: 1.5V - 1.7V
o Green: 1.7V - 1.9V
o Blue: 1.9V - 2.1V
o Yellow: 2.1V - 2.3V
o White: 2.3V - 2.5V
Components:
o Use comparators (e.g., LM339 quad comparator or any other suitable quad amp) to detect voltage thresholds.
o Create reference voltages using a resistor divider network.
o Drive LED based on comparator outputs.
Power Supply: Assume a stable 9V supply for the comparators and LED driving, with the input signal varying between 1.5V and 2.5V.

Circuit Diagram Description
Below is a step-by-step description of the circuit. You can draw this using Eagle

Components Needed
• 5 LEDs: Red, Green, Blue, Yellow, White (each with appropriate forward voltage, typically 2V for Red, 3V for others; use datasheets to confirm).
Resistors: For LED current limiting: per LED (assuming 9V battery supplyt).
o For voltage divider: 10kΩ resistors (adjust for precision).
• Comparators: LM339 (quad comparator, so two ICs for 5 thresholds) or similar.
• Reference Voltage Source: Use a 5V supply with a resistor divider to create reference voltages.
• Transistors or MOSFETs (optional): To drive LEDs if comparator output current is insufficient.
• Power Supply: 5V for comparators and LEDs, plus the 1.5V-2.5V variable input.
Circuit Steps
1. Create Reference Voltages:
o Use a resistor divider with five 10kΩ resistors in series, connected between 5V and ground.
o This creates reference voltages at approximately 1V intervals (adjust resistor values to match desired thresholds).
o To match the 1.5V-2.5V range, scale the divider to produce voltages at:
 1.7V, 1.9V, 2.1V, 2.3V (four thresholds for five windows).
o Example divider: Connect resistors R1 to R5 (each 10kΩ) between 2.5V (top) and 1.5V (bottom), tapping voltages at nodes. Alternatively, use a precision reference IC or trim potentiometers for exact voltages.
2. Comparator Setup:
o Use four comparators to define five voltage windows.
o Comparator thresholds:
 Comp1: 1.7V (Red off, Green on)
 Comp2: 1.9V (Green off, Blue on)
 Comp3: 2.1V (Blue off, Yellow on)
 Comp4: 2.3V (Yellow off, White on)
o Connect the input voltage (1.5V-2.5V) to the non-inverting input of each comparator.
o Connect reference voltages (1.7V, 1.9V, 2.1V, 2.3V) to the inverting inputs.
3. Logic for LED Control:
o Use combinational logic or diode logic to ensure only one LED is on at a time:
 Red LED: On when V_in < 1.7V (Comp1 output low).
 Green LED: On when 1.7V ≤ V_in < 1.9V (Comp1 high, Comp2 low).
 Blue LED: On when 1.9V ≤ V_in < 2.1V (Comp2 high, Comp3 low).
 Yellow LED: On when 2.1V ≤ V_in < 2.3V (Comp3 high, Comp4 low).
 White LED: On when V_in ≥ 2.3V (Comp4 high).
o Implement this using AND gates, transistors, or direct comparator outputs with pull-up resistors.
4. LED Driving:
o Connect each LED to the 5V supply through a 220Ω current-limiting resistor.
o Use the comparator output (or logic gate output) to control a transistor (e.g., NPN like 2N3904) that grounds the LED cathode to turn it on.
o Ensure the comparators open-collector output has a pull-up resistor (e.g., 10kΩ to 5V).
5. Power and Ground:
o Power the LM339 with 5V and connect ground.
o Ensure the input signal (1.5V-2.5V) is clean and stable.