Crosswalk Pedestrian Signal and Homemade Controller

Posted on Feb 7, 2014

The signal has three wires: common, `walk`, and `don`t walk`. This page describes the operation of the unit`s countdown feature. The information and examples provided here should work for other models and brands of signals. Click here togo to the beginning of the article The signal was shipped along with a two-page sheet detailing the use of the countdown timer. You can download

Crosswalk Pedestrian Signal and Homemade Controller
Click here to download the full size of the above Circuit.

a scan of the document here, but I will summarize the details here. The signal was designed to be a drop-in replacement for non-countdown signals. Instead of receiving timing information (such as the length of the countdown or even a separate signal to trigger it), the signal is intelligent and contains a microcontroller that times the length of the "walk" phase and inserts an appropriately-lengthed countdown automatically. This means that the signal needs to be controlled carefully; the length of each "walk" phase cannot change, or else the signal`s countdown will become confused and misaligned. So, if you want the signal to display a 60-second countdown, then the "walk" phase must be exactly one minute in duration every time. In other words, you cannot control the countdown if you are using a manual (hand) switch. You need to use a timer that can provide consistent walk and don`t walk phases. When the signal is powered up, its internal microcontroller will measure the duration of the length of the "walk" phase. It takes the signal two walk/don`t walk cycles to adapt to and measure the time intervals; only after the second cycle does the countdown come on. The microcontroller that runs the display digits and times the phases is powered whenever either the hand or man is illuminated. However, when power is completely removed from the display, the microcontroller forgets the timing details that it had measured. This means...

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