The Circuitron SD-3 is capable of driving any single searchlight style, 2 lead or 3 lead, Bi-Color or Tri-Color, LED-type signal to red, green and amber aspects. Compatible signals are manufactured by Oregon Rail Supply, Tomar, Sunrise Enterprises, ISS and others. Two SD-3s are required for double-head signals. NOTE: The SD-3 will not drive 3 lamp signals (see SD-1 above). Bi-color LEDs contain both a RED and a GREEN chip mounted side by side. Amber is achieved by alternately lighting the red and green LED chips at a high frequency. The eye perceives this mix of red and green as yellow (amber). A hue adjustment is provided on the SD-3 to allow adjusting the amber color. The SD-3 may be controlled by a single-pole, 3 position switch or automatically by detection circuits such as the CIRCUITRON BD-1, BD-2 or BD-3 (minimum of 2 blocks required). Other detection circuits that provide a logic low (ground or -) output may also be used. The SD-3 is constructed on a 2” x 3” printed circuit board and requires a 10 – 18 volts AC or DC input (a DC power source is required when the SD-3 is used with detection circuits).