The CIRCUITRON BD-1 is an advanced, integrated circuit design Block Occupancy Detector utilizing our proven Opto-Electronic design which provides positive indication whenever a block-section of a layout is occupied by any piece of rolling stock. Two pair of CIRCUITRON Opto-Sensors (included) are mounted between the ties at the end points of the block that is to be protected. Any piece of rolling stock entering the block shades the Opto-Sensors from ambient room light which activates the logic circuitry on the BD-1 circuit board. No modifications to rolling stock are necessary. The BD-1 is bidirectional and will give proper indications even if a train leaves a block by reversing direction and backing out. The CIRCUITRON BD-1 also contains driver circuitry sufficient to power a pair of two-color LED (including 2 lead Bi-Color LEDs) or incandescent lamp block signals at each end of the protected block (LED-type signals must be wired with a common anode [ ] configuration). The outputs on the BD-1 can control a maximum of 250 ma. For 3- color signaling, additional signal drivers will be necessary (see our SD-x series of drivers later in this section). The BD-1 requires a 10–18-volt DC input for proper operation. The power supply should be filtered for proper operation.  If you do not have a filtered power supply, the CIRCUITRON PS-1 filtered AC to DC Converter or PS-2 Regulated AC to DC Converter are ideal for this application. The BD-1 is constructed on a 2” x 3” printed circuit board.