I don't know if it has been mentioned but an LDR in a long black tube facing the car would probably do the trick with not much chance of false triggering (triggered by headlights and with no noise, :) )
Australia wildlife can be pretty loud.
But I doubt it will be a problem, unless you have a flock of lyrebirds living nearby.
Sylvia.
Ah yes, I forgot about that, and they're not LEDs (yet).
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Yes that was Sylvia's suggestion and I'll be going with it, at least for starters. I've already gathered up an LDR and some very small black pipe from a garden irrigation system, which will hopefully make it directional. I'll probably try to rig up the sensor on the weekend and look at the readings using my multimeter to determine whether I'll need another sensor to disable it during daylight.
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Yes, I was considering the radio solution when I thought of the horn detector. I don't really like having one of those little control transmitters clattering around the car. Yes I know I'm being terribly fussy, I reserve that right.
I was actually considering building the transmitter control into the car interior somewhere, and it was along that train of thought that I realised using the horn would perhaps be easier than trying to neatly modify a part of the interior.
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Well I built this headlight sensor design, and so far it seems to be working well.
I used a 200mm length of 4mm ID black tubing, cable-tied to length of stiff wire to keep it straight, in an attempt to avoid having to use an ambient light sensor, and it seems to work very well. So far I've only seen resistance readings below Megaohms when the headlights are on, or a torch is shone directly down the tube.
I built the control circuit that I described elsewhere in the thread, and it works well. It is currently set to trigger on any LDR resistance below about 500K, though a trimpot will allow me to adjust this threshold lower if required. So far the only remaining case where I may have to do this is if the light of the sunrise reflecting from the headlight is enough to trigger the circuit, unfortunately I messed up my test this morning to see whether this was a problem.
Obtaining the replacement headlight has turned into a bit of a saga in itself, so it will be another week until I can set up the driveway light anyway. In the mean time the circuit is connected up to a buzzer to let me know of any false triggers.
Thanks for this suggestion. Time will tell whether I will also give my original horn detector idea a go after the driveway light is set up.
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