Preening Raven by Peter Farell with glowing red eye circuitry

Circuit Design of crow with red LED eyes

Power Supply (9V Battery):

• Connect the positive terminal of the 9V battery to the positive rail of your breadboard.
• Connect the negative terminal of the battery to the ground rail.

LDR and Base Resistor:

• One side of the LDR is connected to the positive rail.
• Connect the other side of the LDR to the base of the 2N2222 A331 transistor.
• Place a resistor (try 47kΩ, 33kΩ, or 22kΩ depending on sensitivity needs) between the base of the transistor and ground. This resistor controls the sensitivity to light.

Connecting the LEDs:

• Connect the emitter of the 2N2222 A331 transistor to ground (negative rail).
• Connect the collector of the transistor to the negative terminals (cathodes) of both LEDs.
• Connect a current-limiting resistor (e.g., 330Ω or 220Ω for each LED) in series with each LED. Connect one end of the resistor to the positive terminal of each LED (anode), and the other end to the positive rail of the 9V battery.

Summary of Connections:

LDR and Resistor (Voltage Divider):

• Positive rail ⟶ LDR ⟶ base of 2N2222 A331 transistor.
• Base of 2N2222 ⟶ resistor (22kΩ–47kΩ) ⟶ ground.

Transistor and LEDs:

• Emitter of 2N2222 A331 ⟶ ground.
• Collector of 2N2222 A331 ⟶ cathodes (negative) of both LEDs.
• Each LED’s anode ⟶ current-limiting resistor (330Ω or 220Ω) ⟶ positive rail.

Why This Setup Works

• Light Sensitivity: The LDR and base resistor set up a voltage divider that controls the transistor’s switching based on light levels.
• Current Limiting for LEDs: Using separate resistors for each LED helps ensure they receive a balanced current, giving them equal brightness without overloading the transistor or LEDs.