SigOS: Hardware

The Signal Operating System is designed to operate on low-cost hardware. This encourages extensive use for Signals and Detectors throughout most railroads, large and small.

Components

CdS photoresistor

Closeup of CdS (cadmium sulphide) photoresistor.

A CdS photoresistor is a light-sensitive resistor. It detects the ambient light at the signal head, which SigOS uses to control the brightness of the WS281 LEDs.

• Pin 1
  • Either wire from CdS photoresistor
  • Wire color: Green
  • Function: Variable voltage into GPIO P1 of Control Board A/D converter. Voltage is inversely proportional to ambient light level.
• Pin 2
  • Other wire from CdS photoresistor
  • Wire color: Yellow
  • Function: +3.3 volt power
• Part number: GL5516
• Characteristics: Bright light 5-10k Ohms, dark 0.2M Ohms
• Source: Amazon.com