The Race Timer system incorporates essentially two types of displays to let the riders know they've been detected at the checkpoint. Although the "Cadillac" solution is the remote LED display, the system also supports a stoplight.

Shown to the left is a stoplight which was customized by one of the users of the Race Timer system.  The stoplight is delivered with only the central component - the stand was constructed by the users. As delivered, lenses are visible on all four sides of the stoplight.

The center light is not used - I put a buzzer in the yellow lens. There's also a small switch visible just to the right of the yellow lens, used to turn the buzzer on or off - if you'd prefer to eliminate the extra noise at the checkpoint. In reality everyone leaves the buzzer on, letting the team doing any manual backup know the rider was detected.

The stoplight system uses 12 volts from the power supply used elsewhere in the system for operating the RFID components - and connects to the printer port for the on / off signals from the computer. The black box houses the relays which couple the 12 Volt power supply to the red / green lens.

In normal operation the red light is essentially illuminated constantly. As a rider is detected, the the red light is turned off and the green light is turned on.  The green light remains on for 1/3 second, then the system reverts back to a red light. The buzzer sounds for the duration the green light is on.

While it might seem that 1/3 second is not enough for the green light, experience shows that it's more than enough. The optimum is to have a green light on long enough that the rider will detect it, yet not stay on so long that a rider immediately behind him will go through while the green light is still lit.  After a fair amount of testing, it seems that 1/3 second is a good mix - enabling adequate signaling for the rider at the checkpoint, yet fast enough to have returned back to red before the next rider passes through.