Auto-headlights is moderately difficult because of the length of the delays and the quiesient current. Probably best done with a microcontroller; Light level sensing is generally time based and then it stays on until the ignition is turned off. I don't know what the times are. But take going under a bridge a mile long or so. I think it takes about 20 so for the lights to turn on, Never paid attention to the off threshold/time.
I can, however, offer you a simple design that I used in 1982 on my vehicle.
In that particular vehicle, there was +12 available when the tail lights were on and ground via the driver's door switch, when the driver's door was opened.
There was already a isolation diode there anyway, so I took advantage of it.
I had an EASY way of "buzzer on if lights were on and driver's door was open".
So, (to +12 when parking lights on), a piezo buzzer and a diode to the driver's door switch (ground when open, +12 when closed).
I had to replace the buzzer a few times in 17 years. The high temperature kills them.
Now, one car has the
1. Lights stay on until the driver's door is opened (actually radio too)
2. A few different delays are possible for how long the lights stay on.
1. Lights turn off when the door is opened and car is off.
Both have auto-on by daylight sense.
In BOTH of these cases, in order to turn-off the lights when the engine is on, you have to do something heroic.
Turn-off car and open the door. Turn off the headlights. if they are on.
Stop. Turn off car, engage parking brake. Turn on car which will turn off lights.
If you want to start the engine with the lights off, the parking brake must be set. Turning them off is not so easy. Blinking the high beams is easy on car #2 (momentary and full on stalk switch). In car #1 it's not possible.
For auto-on; timed off, there are a lot of issues to deal with.
Turning the lights off briefly is very useful if you confront a deer.
This forum is a continuation of the printed column "Q&A", where I answer questions about all aspects of electronics, including computer hardware, software, circuits, electronic theory, troubleshooting, and anything else of interest to the hobbyist. Feel free to participate with your questions, comments or suggestions on answers printed in the magazine. Send all NEW questions to: [email protected]
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