Light Activated Train Detector Circuits
Using the popular 555 timer IC as a photocell controlled train detector.
Shown on the schematic is a secondary output that uses the open collector at the DISCHARGE terminal (Pin 7) of the timer. This output can sink a fairly large current and would be ideal for driving relays.
Circuit 2: Using Photocells
Circuit 3: Photocell with delayed release
The next circuit uses two LM555 timers to provide train detection with a delay in the signal returning to the unoccupied condition
LM555 Photo-Detector Circuit Notes
- Inductive loads such as relay solenoids should have anti-ringing diodes across their coils.
- The use of R6 in the circuit would make this type of detector more suitable for use with photo transistors.
- Resistor R1 is used to prevent excessive current flow to the THRESHOLD terminal of the timer ar through the photocell if R2 is set to a zero position.
- Cadmium Sulfide photo-resistors come in a wide variety of characteristics and ratings. Some testing and adjustment may be required to get reliable detection with this circuit
Circuit Credit: Rob Paisley