Bicolor LED Driver Uses Two Leads

This circuit detects the correct closed condition of the left and right side bags in a motorcycle companion. The bag has two locks that you must close for protection.

Bicolor LED Driver Uses Two Leads Circuit Diagram:

When you push the two momentary SPDT (single-pole/double-throw) switches, they sense the correct closed bag. One bicolor red-and-green LED indicates the bag’s status, with the red color showing the open-bag condition. To illuminate the LEDs, you must reverse the polarity of the applied voltage to the LED to change the color (Table 1).

Diodes D₁ and D₂ and resistor R₁ form a discrete OR gate. When either pushbutton switch connects to 12V, the voltage at Point A is positive with respect to Point B. Transistor Q₁ conducts, letting current illuminate the red LED. When neither switch connects to 12V, neither diode conducts. The base of Q₁ pulls low through R₁ and R₄, indicating that the bags are closed. Thus, the green LED illuminates as current passes through it and through R₁ and R₂.

The diode, transistor, and resistor values are not critical, and you can adjust them according to your needs. You can also replace the bicolor LED with two discrete LEDs of different colors placed back to back.