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

On 20/04/15 11:31, 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


I would say: flush mount a reed switch in the door surround next or just
under the flap. Glue a small but powerful magnet to the flap.

On 20/04/2015 11:41, Tim Watts wrote:

I would say: flush mount a reed switch in the door surround next or just
under the flap. Glue a small but powerful magnet to the flap.

Just buy an alarm door contact or even one of those cheap battery
powered window alarms they had in poundland, self adhesive, contain a
reed switch and a sounder. I think they were a pound for four, I bought
some because I wanted the batteries for something else.

On Monday, 20 April 2015 11:31:54 UTC+1, 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

Simplest is a microswitch. But the flap needs to move away from it to trigger, could glue a piece to the rear of the flap very close to the hinge to create that


NT

On 20/04/2015 11:31, 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

What about fitting a tiny tilt switch, maybe in series with a doorbell?
A very simple solution, or is that a silly idea.

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.

I should have though that the simplest would be a standard battery
bell circuit with a microswitch on a springy piece of wire behind the
flap replacing the bell push. Adjust the microswitch position so that
it is far enough behind the flap not to be set off by gusts of wind
but close enough that any post passing through the flap will trigger
it. The springy piece of wire should be springy enough to allow the
flap to open fully and the microswitch to return to the waiting
position each time the flap closes.

It won't look terribly elegant.

Nick

"Bod" wrote in message
...
On 20/04/2015 11:31, 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

What about fitting a tiny tilt switch, maybe in series with a doorbell?
A very simple solution, or is that a silly idea.

Not that easy to have a connection to it that will last for decades.

On 20/04/2015 12:21, Rod Speed wrote:


"Bod" wrote in message
...
On 20/04/2015 11:31, 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

What about fitting a tiny tilt switch, maybe in series with a doorbell?
A very simple solution, or is that a silly idea.

Not that easy to have a connection to it that will last for decades.

Ok, what about a reed switch or a magnetic switch in unison with a
separate buzzer/bell? Or don't you think that will last?

On Mon, 20 Apr 2015 11:41:28 +0100, Tim Watts
wrote:

On 20/04/15 11:31, 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


I would say: flush mount a reed switch in the door surround next or just
under the flap. Glue a small but powerful magnet to the flap.
You can get change over reed switches (google it). Wire it to use the
contact pair that closes when the magnet on the flap moves away from
the switch.

On Monday, 20 April 2015 12:32:28 UTC+1, Bod wrote:
On 20/04/2015 12:21, Rod Speed wrote:


"Bod" wrote in message
...
On 20/04/2015 11:31, 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

What about fitting a tiny tilt switch, maybe in series with a doorbell?
A very simple solution, or is that a silly idea.

Not that easy to have a connection to it that will last for decades.

Ok, what about a reed switch or a magnetic switch in unison with a
separate buzzer/bell? Or don't you think that will last?

No, you'd need to feed the reed switch output to a transistor, use that to drive the bell. Reeds have very low ampacity.


NT

Is the issue that stuff is left in the opening making it stay open, or does
it always snap back every time. I ask as it would have a bearing on the
design, ie, latching or non latching.

What would I do? Small hall effect IC, and a relay with a magnet on the
flap.

These only have three leads like a transistor and detect the magnet either
being there or not, so really its a case of where you glue your magnet or
you could just use the hall effect device to operate a changover relay, or
you could use it to just bias on or off a transistor if you don't want to
use a relay.

BY the way, many of the cheaper door phones use a very handy way to make the
door bell sound. They wire the outside speaker/micropphone though a
capacitor, and then, shorting this out triggers the noise, so if you
already have a door phone, one could design a basic simple microswitch on
the flap so as it is pushed out, it shorts the capacitor and sets off the
door bell.
Of cours this might cause confusion as both the door bell and the flap would
sound the door bell!
Brian

--
From the Sofa of Brian Gaff Reply address is active
"MM" wrote in message
...
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

"Bod" wrote in message
...
On 20/04/2015 12:21, Rod Speed wrote:


"Bod" wrote in message
...
On 20/04/2015 11:31, 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

What about fitting a tiny tilt switch, maybe in series with a doorbell?
A very simple solution, or is that a silly idea.

Not that easy to have a connection to it that will last for decades.

Ok, what about a reed switch or a magnetic switch

Yeah, that's a much better approach because the switch
and the wiring to it can be on the fixed part of the door
and its trivial to make it completely invisible too if you want.

in unison with a separate buzzer/bell?

Or don't you think that will last?

Yeah, that will last fine.

Davidm wrote:

You can get change over reed switches (google it). Wire it to use the
contact pair that closes when the magnet on the flap moves away from
the switch.

That could provide a signal of the right sense.

Does the OP need a circuit which latches, for the rare occasion
when the postie doesn't leave the mail stuck in the flap, with a
gale howling through the gap? ;-)

Chris
--
Chris J Dixon Nottingham UK


Plant amazing Acers.

On 20/04/2015 12:58, Rod Speed wrote:


"Bod" wrote in message
...
On 20/04/2015 12:21, Rod Speed wrote:


"Bod" wrote in message
...
On 20/04/2015 11:31, 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

What about fitting a tiny tilt switch, maybe in series with a doorbell?
A very simple solution, or is that a silly idea.

Not that easy to have a connection to it that will last for decades.

Ok, what about a reed switch or a magnetic switch

Yeah, that's a much better approach because the switch
and the wiring to it can be on the fixed part of the door
and its trivial to make it completely invisible too if you want.

in unison with a separate buzzer/bell?

Or don't you think that will last?

Yeah, that will last fine.

Righto.

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?

Both operate when the door is opened.



--
Windows 8.1 on PCSpecialist box

On Monday, 20 April 2015 12:50:55 UTC+1, wrote:
On Monday, 20 April 2015 12:32:28 UTC+1, Bod wrote:
On 20/04/2015 12:21, Rod Speed wrote:


"Bod" wrote in message
...
On 20/04/2015 11:31, 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

What about fitting a tiny tilt switch, maybe in series with a doorbell?
A very simple solution, or is that a silly idea.

Not that easy to have a connection to it that will last for decades.

Ok, what about a reed switch or a magnetic switch in unison with a
separate buzzer/bell? Or don't you think that will last?


you could use a lever micro switch such as this
http://www.rapidonline.com/design-te...r-ip67-50-2600

No, you'd need to feed the reed switch output to a transistor, use that to drive the bell. Reeds have very low ampacity.

depends on the bell I'd use a buzzer and this switch takes up to 0.5amps
http://www.rapidonline.com/design-te...switch-78-1002

have to make sure the right type with regard to normally open or normally closed.



NT

On Mon, 20 Apr 2015 13:01:15 +0100, Chris J Dixon
wrote:

Davidm wrote:

You can get change over reed switches (google it). Wire it to use the
contact pair that closes when the magnet on the flap moves away from
the switch.

That could provide a signal of the right sense.

Does the OP need a circuit which latches, for the rare occasion
when the postie doesn't leave the mail stuck in the flap, with a
gale howling through the gap? ;-)

Well, that doesn't happen, but it would be nice to have the alarm
alert for 10 seconds before switching off. For starters, it's enough
to just have the gadget sound once. For just a letter, it wouldn't
sound for very long, but I usually get either no mail or a bundle of
up to four items and it takes longer to push those through.

MM

On Mon, 20 Apr 2015 11:54:03 +0100, Nick Odell
wrote:

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.

I should have though that the simplest would be a standard battery
bell circuit with a microswitch on a springy piece of wire behind the
flap replacing the bell push. Adjust the microswitch position so that
it is far enough behind the flap not to be set off by gusts of wind
but close enough that any post passing through the flap will trigger
it. The springy piece of wire should be springy enough to allow the
flap to open fully and the microswitch to return to the waiting
position each time the flap closes.

That's not a bad idea, actually. Dunno where I'd find such a piece of
wire, though.

It won't look terribly elegant.

Not unduly worried about that.

MM

On Mon, 20 Apr 2015 12:56:27 +0100, "Brian Gaff"
wrote:

Is the issue that stuff is left in the opening making it stay open, or does
it always snap back every time. I ask as it would have a bearing on the
design, ie, latching or non latching.

No, the issue is that I need to catch the postie when he's about to
leave a card because a book or similar package from Amazon is too
large to fit through the flap. I've got TWO bell pushes, but sometimes
the dozy geezer doesn't ring either, he just taps on the door and I
don't hear it. But if he's maybe already stuffed a letter through,
then I would already have that alert to go on, rush downstairs and
open the door as he's departing whereupon he's pretty much obliged to
come back and hand me the parcel. And if he's only stuffing the
collection card through, then that would be enough to trigger the
letterbox flap alert.

I tried doing this, i.e. monitoring the postal deliveries, with VLC
and a web cam which streams the video capture to another networked PC,
but I have to be there to watch the remote display. VLC does have an
option to flash up changes from one frame to the next, but I haven't
found how to link those changes to an audible alert. Plus, it would
give all kinds of false triggers as other residents walk past my
house.

That's when I thought of the letterbox flap.


What would I do? Small hall effect IC, and a relay with a magnet on the
flap.

These only have three leads like a transistor and detect the magnet either
being there or not, so really its a case of where you glue your magnet or
you could just use the hall effect device to operate a changover relay, or
you could use it to just bias on or off a transistor if you don't want to
use a relay.

BY the way, many of the cheaper door phones use a very handy way to make the
door bell sound. They wire the outside speaker/micropphone though a
capacitor, and then, shorting this out triggers the noise, so if you
already have a door phone, one could design a basic simple microswitch on
the flap so as it is pushed out, it shorts the capacitor and sets off the
door bell.
Of cours this might cause confusion as both the door bell and the flap would
sound the door bell!
Brian

Yep, been giving it some more thought off and on throughout today.

MM

On 20 Apr 2015 14:06:02 GMT, David wrote:

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?

Both operate when the door is opened.

I just checked my fridge and that has the switch pushed in by the
relatively heavy fridge door when closed and the light is off. The
switch is spring-loaded so that when the door is opened the switch
operates, closes contacts in its innards somewhere and the light comes
on.

In principle the idea is sound, but the flap wouldn't be anything like
heavy enough to depress this particular switch when the flap is
closed. A much, MUCH weaker spring would be needed. But probably
doable.

MM

On 20/04/2015 16:54, MM wrote:

No, the issue is that I need to catch the postie when he's about to
leave a card because a book or similar package from Amazon is too
large to fit through the flap. I've got TWO bell pushes, but sometimes
the dozy geezer doesn't ring either, he just taps on the door and I
don't hear it. But if he's maybe already stuffed a letter through,
then I would already have that alert to go on, rush downstairs and
open the door as he's departing whereupon he's pretty much obliged to
come back and hand me the parcel. And if he's only stuffing the
collection card through, then that would be enough to trigger the
letterbox flap alert.

You need a PIR connected to a chime, then it detects him walking up and
not pushing anything through the flap.

You can buy them as cordless battery operated.

On Mon, 20 Apr 2015 17:01:58 +0100, MM wrote:

On 20 Apr 2015 14:06:02 GMT, David wrote:

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?

Both operate when the door is opened.

I just checked my fridge and that has the switch pushed in by the
relatively heavy fridge door when closed and the light is off. The
switch is spring-loaded so that when the door is opened the switch
operates, closes contacts in its innards somewhere and the light comes
on.

In principle the idea is sound, but the flap wouldn't be anything like
heavy enough to depress this particular switch when the flap is closed.
A much, MUCH weaker spring would be needed. But probably doable.

MM

I refer the honourable member to my second option - courtesy light switch.

Plunger switch held away from the contact by pressure, and the contacts
closed by a spring when the door is opened.



--
Windows 8.1 on PCSpecialist box

In my rummage box I found a 20-year-old (at least) Polycell door
alarm! White in colour, this measures about 125mm x 33mm x 25mm. It
runs on a 9V battery, which, believe it or not STILL had enough power
to emit a few feeble clicks from the buzzer when I switched it on and
played around with the keeper.

Yes, there's a keeper to go on the door; the alarm is screwed to the
door frame. I never used it. It was a flash in the pan idea when I
lived near High Wycombe which had a high crime rate.

Now, I've dismantled the thing! The circuit board inside (approx 65mm
x 30mm) was fixed with two plastic "rivets" which I drilled out in
seconds.

With a new 9V battery the alarm is nice and loud as I remember it.

Without the casing gubbins around it, this is quite small and compact
enough to mount on the letterbox flap. But the 64,000 dollar question
is, how long could I extend the two wires leading to the buzzer?

The buzzer looks like a small round black drum, approx 12mm dia and
about 15mm long. It has 2 wires coming out of it. It is marked P87J.

How about 3 metres? 10? I'd use bell cable or similar. Would extending
it by such a length eventually "blow" the components on the circuit
board (extra stress pumping the signal that much further)?

MM

On 20/04/2015 19:07, MM wrote:
In my rummage box

Have you tried a little card next to the letterbox:

"Please ring the bell after you put anything through the letter box.
Thanks."

That would be effective, and "simplest possible".

MM wrote:
I want to hear an alarm sound/see an LED flash when the postie posts
something through my letterbox.

I'd say use an alarm contact with its magnet as your trigger, e.g.

https://securitywarehouse.co.uk/catalog/-p-2544.html

Or put a post-it note on the door asking the postie to ring the doorbell
whenever they deliver something :-)

On Monday, 20 April 2015 19:07:18 UTC+1, MM wrote:
Without the casing gubbins around it, this is quite small and compact
enough to mount on the letterbox flap. But the 64,000 dollar question
is, how long could I extend the two wires leading to the buzzer?
The buzzer looks like a small round black drum, approx 12mm dia and
about 15mm long. It has 2 wires coming out of it. It is marked P87J.
How about 3 metres? 10?

Any reasonable distance if the buzzer is the sort with internal driver circuitry and the alarm is only sending DC volts down the wire.

Not sure if it's a bare piezo sounder relying on a driver circuit on the main alarm board.

Owain

"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 dont have something
you can pinch and use on your letterbox.

Even older ones arent mechanically suitable.

On 20/04/2015 11:53, Bod wrote:
On 20/04/2015 11:31, 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

What about fitting a tiny tilt switch, maybe in series with a doorbell?
A very simple solution, or is that a silly idea.

I think you mean in parallel (with the bell push). Still readily
available (Maplin, Farnell) but alas you can no longer get the reliable,
high capacity mercury ones from RS which the IRA used to use.

"MM" wrote in message
...
In my rummage box I found a 20-year-old (at least) Polycell door
alarm! White in colour, this measures about 125mm x 33mm x 25mm. It
runs on a 9V battery, which, believe it or not STILL had enough power
to emit a few feeble clicks from the buzzer when I switched it on and
played around with the keeper.

Yes, there's a keeper to go on the door; the alarm is screwed to the
door frame. I never used it. It was a flash in the pan idea when I
lived near High Wycombe which had a high crime rate.

Now, I've dismantled the thing! The circuit board inside (approx 65mm
x 30mm) was fixed with two plastic "rivets" which I drilled out in
seconds.

With a new 9V battery the alarm is nice and loud as I remember it.

Without the casing gubbins around it, this is quite small and compact
enough to mount on the letterbox flap. But the 64,000 dollar question
is, how long could I extend the two wires leading to the buzzer?

The buzzer looks like a small round black drum, approx 12mm dia and
about 15mm long. It has 2 wires coming out of it. It is marked P87J.

How about 3 metres? 10? I'd use bell cable or similar. Would extending
it by such a length eventually "blow" the components on the circuit
board (extra stress pumping the signal that much further)?

Should be fine for any distance you like in a house.

On Monday, 20 April 2015 22:00:04 UTC+1, newshound wrote:
I think you mean in parallel (with the bell push). Still readily
available (Maplin, Farnell) but alas you can no longer get the reliable,
high capacity mercury ones from RS which the IRA used to use.


This apparently will switch a buzzer from a 9v battery

http://www.maplin.co.uk/p/non-mercury-tilt-switch-dp50e

A possible source might be the pendulum tilt switches used for heater safety cut-offs eg
http://www.4delonghi.co.uk/tilt-swit...t.pl?pid=97213

Float switches using microswitches and weights have high current capacity but lack finess in operating angles.

http://www.tritoncontrols.co.uk/asse...lagnew2008.pdf

Mercury switches still appear to be available; this supplier mentions ratings of associated connection leads up to 40 amp

http://www.russell-scientific.co.uk/...tches-21-c.asp

Owain

On Mon, 20 Apr 2015 16:44:03 +0100, MM wrote:

On Mon, 20 Apr 2015 11:54:03 +0100, Nick Odell
wrote:

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.

I should have though that the simplest would be a standard battery
bell circuit with a microswitch on a springy piece of wire behind the
flap replacing the bell push. Adjust the microswitch position so that
it is far enough behind the flap not to be set off by gusts of wind
but close enough that any post passing through the flap will trigger
it. The springy piece of wire should be springy enough to allow the
flap to open fully and the microswitch to return to the waiting
position each time the flap closes.

That's not a bad idea, actually. Dunno where I'd find such a piece of
wire, though.

I was thinking of something that worked along the lines of an ironing
board flex holder. Not necessarily this one:
http://ecx.images-amazon.com/images/...cL._SY355_.jpg

but something that is both stiff enough to hold the switch in place
and bendy enough to fold out of the way when the flap is opened.

Nick

On 20 Apr 2015 18:01:51 GMT, David wrote:

On Mon, 20 Apr 2015 17:01:58 +0100, MM wrote:

On 20 Apr 2015 14:06:02 GMT, David wrote:

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?

Both operate when the door is opened.

I just checked my fridge and that has the switch pushed in by the
relatively heavy fridge door when closed and the light is off. The
switch is spring-loaded so that when the door is opened the switch
operates, closes contacts in its innards somewhere and the light comes
on.

In principle the idea is sound, but the flap wouldn't be anything like
heavy enough to depress this particular switch when the flap is closed.
A much, MUCH weaker spring would be needed. But probably doable.

MM

I refer the honourable member to my second option - courtesy light switch.

Plunger switch held away from the contact by pressure, and the contacts
closed by a spring when the door is opened.

It's probably quite easy to make a small plunger from scratch, using
small tubing or things that can be used as tubes. At QD (shop chain in
Lincolnshire) they have a whole range of yellow boxes with assortments
of screws, nuts and, yes, SPRINGS! They even do an assorted set of
rubber washers, I believe, which could double up as insulators.

In fact, the more I think about this the better I like it, because it
would not require any electronics of any kind (except the battery,
plunger, wire and buzzer or bell). Dunno quite how to mount a plunger
on the letterbox flap, though. It must not provide any resistance to
opening the flap, else the postie will leave stuff sticking out.

MM

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. It's kind of a Blue Peter thing.

MM

On Mon, 20 Apr 2015 20:45:28 +0100, Andy Burns
wrote:

MM wrote:
I want to hear an alarm sound/see an LED flash when the postie posts
something through my letterbox.

I'd say use an alarm contact with its magnet as your trigger, e.g.

https://securitywarehouse.co.uk/catalog/-p-2544.html

Or put a post-it note on the door asking the postie to ring the doorbell
whenever they deliver something :-)

Not sure whether he can read... certainly dozy enough to deliver the
wrong mail to me, or my mail next door sometimes. Plus, not ring the
bell when necessary. Once he handed me a packet that clearly needed
signing for, so I asked, shall I sign then? And he said with a grin,
nah, that's okay. Couldn't be bothered to dig out his doubry and
stylus. (Maybe he'd forgot to being it.)

MM

On Mon, 20 Apr 2015 19:48:47 +0100, GB
wrote:

On 20/04/2015 19:07, MM wrote:
In my rummage box

Have you tried a little card next to the letterbox:

"Please ring the bell after you put anything through the letter box.
Thanks."

That would be effective, and "simplest possible".

Each bell push has a laser printed label (had so for months) saying
"Please ring BOTH bells!" You have to realise that not everyone can
read nowadays. They can recognise house numbers and somehow they work
out which street or road they're on, and that's about as far as their
academic experience ever went. My postie (well, one of them; I get
several different ones) can't even tell the difference between 7 and
5, because sometimes I get the neigbour's mail and she gets mine.

MM

On Mon, 20 Apr 2015 12:54:53 -0700 (PDT),
wrote:

On Monday, 20 April 2015 19:07:18 UTC+1, MM wrote:
Without the casing gubbins around it, this is quite small and compact
enough to mount on the letterbox flap. But the 64,000 dollar question
is, how long could I extend the two wires leading to the buzzer?
The buzzer looks like a small round black drum, approx 12mm dia and
about 15mm long. It has 2 wires coming out of it. It is marked P87J.
How about 3 metres? 10?

Any reasonable distance if the buzzer is the sort with internal driver circuitry and the alarm is only sending DC volts down the wire.

Not sure if it's a bare piezo sounder relying on a driver circuit on the main alarm board.

Will it screw the circuit board if I experiment with different
lengths? Will the buzzer just get quieter and quieter?

MM

On Tue, 21 Apr 2015 07:49:26 +1000, "Rod Speed"
wrote:



"MM" wrote in message
.. .
In my rummage box I found a 20-year-old (at least) Polycell door
alarm! White in colour, this measures about 125mm x 33mm x 25mm. It
runs on a 9V battery, which, believe it or not STILL had enough power
to emit a few feeble clicks from the buzzer when I switched it on and
played around with the keeper.

Yes, there's a keeper to go on the door; the alarm is screwed to the
door frame. I never used it. It was a flash in the pan idea when I
lived near High Wycombe which had a high crime rate.

Now, I've dismantled the thing! The circuit board inside (approx 65mm
x 30mm) was fixed with two plastic "rivets" which I drilled out in
seconds.

With a new 9V battery the alarm is nice and loud as I remember it.

Without the casing gubbins around it, this is quite small and compact
enough to mount on the letterbox flap. But the 64,000 dollar question
is, how long could I extend the two wires leading to the buzzer?

The buzzer looks like a small round black drum, approx 12mm dia and
about 15mm long. It has 2 wires coming out of it. It is marked P87J.

How about 3 metres? 10? I'd use bell cable or similar. Would extending
it by such a length eventually "blow" the components on the circuit
board (extra stress pumping the signal that much further)?

Should be fine for any distance you like in a house.

Whew! That's good news!

MM

On 20/04/2015 12:50, wrote:
On Monday, 20 April 2015 12:32:28 UTC+1, Bod wrote:
On 20/04/2015 12:21, Rod Speed wrote:


"Bod" wrote in message
...
On 20/04/2015 11:31, 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

What about fitting a tiny tilt switch, maybe in series with a doorbell?
A very simple solution, or is that a silly idea.

Not that easy to have a connection to it that will last for decades.

Ok, what about a reed switch or a magnetic switch in unison with a
separate buzzer/bell? Or don't you think that will last?

No, you'd need to feed the reed switch output to a transistor, use that to drive the bell. Reeds have very low ampacity.

Use a hall effect transistor and you can dispense with the reed switch.
You then have a "switch" with no moving parts that will last "forever".


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"MM" wrote in message
...
On 20 Apr 2015 18:01:51 GMT, David wrote:

On Mon, 20 Apr 2015 17:01:58 +0100, MM wrote:

On 20 Apr 2015 14:06:02 GMT, David wrote:

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?

Both operate when the door is opened.

I just checked my fridge and that has the switch pushed in by the
relatively heavy fridge door when closed and the light is off. The
switch is spring-loaded so that when the door is opened the switch
operates, closes contacts in its innards somewhere and the light comes
on.

In principle the idea is sound, but the flap wouldn't be anything like
heavy enough to depress this particular switch when the flap is closed.
A much, MUCH weaker spring would be needed. But probably doable.

MM

I refer the honourable member to my second option - courtesy light switch.

Plunger switch held away from the contact by pressure, and the contacts
closed by a spring when the door is opened.

It's probably quite easy to make a small plunger from scratch, using
small tubing or things that can be used as tubes. At QD (shop chain in
Lincolnshire) they have a whole range of yellow boxes with assortments
of screws, nuts and, yes, SPRINGS! They even do an assorted set of
rubber washers, I believe, which could double up as insulators.

In fact, the more I think about this the better I like it, because it
would not require any electronics of any kind (except the battery,
plunger, wire and buzzer or bell). Dunno quite how to mount a plunger
on the letterbox flap, though. It must not provide any resistance to
opening the flap, else the postie will leave stuff sticking out.

I much prefer the other approach, a reed switch or hall effect sensor
mounted on the door itself and a magnet on the letterbox flap.

Much easier to do and looks better too.

"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.