I'd like a simple switch that triggers when a flashing light is detected. Purpose is to open gate by flashing car headlights (say 3 times).
I have looked at comparators and photoresistors and various MOSFET devices that compare ambient light to further input (point photoresistors in different directions so headlights will trigger a detectable difference even in daylight - they are very sensitive), read about optocouplers and many other devices but get lost in it all and no solution yet for how to accomplish this.
I've looked at comparators the most and they have become really sensitive and cheap, and are adjustable to trigger at determined millivolt difference. They have a lot of use in quality control devices.
Switch would have to be tolerant of different light intensities and flashing rate, basically just measuring 3 discrete voltage differences within, say, 5 seconds as a trigger and then sent to a relay, I suppose. I'd adjust the comparator until I found the sweet spot between noise and intentional flashing.
Seems like there's got to be similar devices for momentary switches; push once for one action, twice for another, etc, within a given time. Seems so familiar but I can't remember a specific device. Many small things (like my circuit tester, mp3 player) scroll through a menu with each button push (which would be like the comparator sending a signal). I could leave the first couple menu items blank, have 3-4 signal events (like button pushes) have the open gate command. But what CMOS or MOSFET can be set up for that?
I would like it to be simple and rugged for outdoor use on the gates. I've heard of strobe detectors used by emergency services to change traffic lights but only word of mouth on that. Security isn't an issue as this would be an additional switch that could be turned on/off and mostly the gates are used for animal control.
Oh, and purpose is also to not have to give everyone an RF module and to allow guests to use it without anyone else activating gates or having to get out of car (some places are quite muddy, narrow, dark, steep edges, no good place for input code box to be mounted). Motion detectors or garage door type light beam won't work because animals can trigger it.
I'm a novice but have repaired many devices, built LED drivers, battery chargers, RC vehicles, large & small appliances, heavy equipment. I was inspired it was doable when we built a game device (Family Feud style with two buttons, first to press activates lights and buzzer and locks out the other button) and the plans online were very complex with multiple transistors and CMOS chips but we did it using just two off the shelf automotive relays.