"MM" wrote in message
...
On Tue, 21 Apr 2015 06:20:03 +1000, "Rod Speed"
wrote:



"David" wrote in message
...
On Mon, 20 Apr 2015 11:31:51 +0100, MM wrote:

I want to hear an alarm sound/see an LED flash when the postie posts
something through my letterbox. The letterbox has a flap on the inside
to keep draughts down. I want to attach 2 contacts to the flap and body
such that as soon as the flap opens and the contacts are broken, said
alarm/LED are triggered.

I'm worse than a novice in electronics, although I've painstakingly
soldered Velleman kits and similar before. I don't know the first thing
about circuit design, but I know enough to know what a resistor is and
what the coloured rings represent. Also, capacitors, transistors and,
above all, DIL chips such as the CMOS 4000 series.

I've reviewed several circuits on the internet, but they all seem
overkill for what I need. The problem, it seems, is getting the thing
to
trigger when the circuit is OPENED.

Thanks.

MM

Car courtesy light or fridge light?

But neither work too well on a letterbox
flap, particularly the car courtesy lights.

Both operate when the door is opened.

But modern cars don't have something
you can pinch and use on your letterbox.

Even older ones arent mechanically suitable.

But a simple plunger could be fabricated from,
say, a nail, a bit of tubing and a small coil spring.

Yes, but I prefer to keep the mechanicals as simple
as possible because that is much more reliable.

It's kind of a Blue Peter thing.

I've always preferred a decent modern electrical approach myself.