# Wireless doorbell switch

Discussion in 'Electronic Basics' started by BoB, May 13, 2005.

1. ### BoBGuest

Hi

Is it possible to convert the output of a wireless

Doorbell to power a small relay or switch?

Bob

BoB, May 13, 2005

2. ### Rheilly PhoullGuest

One day BoB got dressed and committed to text

> Hi
>
> Is it possible to convert the output of a wireless
>
> Doorbell to power a small relay or switch?
>
>
> Bob

If you have to ask, it might be beyond your capabilities but it should be a
relatively simple task to divert the output of the reciever to control relay
or whatever.
Thats a pretty broad question BTW

--
Regards ..... Rheilly Phoull

Rheilly Phoull, May 14, 2005

3. ### Terry PinnellGuest

"BoB" <> wrote:

>Hi
>
>Is it possible to convert the output of a wireless
>
>Doorbell to power a small relay or switch?
>
>
>Bob
>

Here are examples of two simple circuits I've used to do that:
http://www.terrypin.dial.pipex.com/Images/Doorbell-Interfaces.gif

--
Terry Pinnell
Hobbyist, West Sussex, UK

Terry Pinnell, May 14, 2005
4. ### BoBGuest

"Terry Pinnell" <> wrote in message
news:...
> "BoB" <> wrote:
>
> >Hi
> >
> >Is it possible to convert the output of a wireless
> >
> >Doorbell to power a small relay or switch?
> >
> >
> >Bob
> >

>
> Here are examples of two simple circuits I've used to do that:
> http://www.terrypin.dial.pipex.com/Images/Doorbell-Interfaces.gif
>

Thanks for that Terry, I am building a set of starting lights
for mini moto racing, im using a 555 and a 4017 to give
the "Christmas tree" effect. I just need a way of starting the count from
the start line, so I figured a wireless doorbell would be a cheap
option, Wilkos sell them for under £5.
Im planning to hook the output up to the reset pin of the 4017 to
start the sequence. Maybe leave the first couple of outputs unused
to allow for any false starts due to the chime pattern of the doorbell.
Hope Im making sense now, I realise my first question was a little vague.

Bob

BoB, May 14, 2005
5. ### Rich GriseGuest

On Sat, 14 May 2005 09:24:57 +0100, BoB wrote:

>
> "Terry Pinnell" <> wrote in message
> news:...
>> "BoB" <> wrote:
>>
>> >Hi
>> >
>> >Is it possible to convert the output of a wireless
>> >
>> >Doorbell to power a small relay or switch?
>> >
>> >
>> >Bob
>> >

>>
>> Here are examples of two simple circuits I've used to do that:
>> http://www.terrypin.dial.pipex.com/Images/Doorbell-Interfaces.gif
>>

> Thanks for that Terry, I am building a set of starting lights
> for mini moto racing, im using a 555 and a 4017 to give
> the "Christmas tree" effect. I just need a way of starting the count from
> the start line, so I figured a wireless doorbell would be a cheap
> option, Wilkos sell them for under £5.
> Im planning to hook the output up to the reset pin of the 4017 to
> start the sequence. Maybe leave the first couple of outputs unused
> to allow for any false starts due to the chime pattern of the doorbell.
> Hope Im making sense now, I realise my first question was a little vague.

The question wasn't vague to me, but the only answer I have is "It depends
on what the doorbell receiver's output is." For example, if it has a
physical, electromechanical chime, with visible wires to the receiver,
then it's probably a DC signal that'd be trivial to hook to a relay.
(You'd just replace the chime with the relay coil). But if the doorbell
has its own oscillator and speaker, then you would need to pick up the
signal off the speaker leads, but then you'd have to do some "signal
conditioning", and what kind of conditioning you do depends on what kind
of speaker it is, what the sounds are that it's outputting, and so on.

I picked up the signal to the little piezo beeper in an alarm clock
once, but it was just a pulse train. I used a capacitor to "sense"
the pulse train and trigger a one-shot (monostable multivibrator),
that would trigger on the first pulse, and hold _its_ output active
for A) as long as the alarm was alarming, since it was a retriggerable
one-shot, plus B) the time-out of the one- shot after the last pulse.

Good Luck!
Rich

Rich Grise, May 14, 2005
6. ### Terry PinnellGuest

"BoB" <> wrote:

>
>"Terry Pinnell" <> wrote in message
>news:...
>> "BoB" <> wrote:
>>
>> >Hi
>> >
>> >Is it possible to convert the output of a wireless
>> >
>> >Doorbell to power a small relay or switch?
>> >
>> >
>> >Bob
>> >

>>
>> Here are examples of two simple circuits I've used to do that:
>> http://www.terrypin.dial.pipex.com/Images/Doorbell-Interfaces.gif
>>

>Thanks for that Terry, I am building a set of starting lights
>for mini moto racing, im using a 555 and a 4017 to give
>the "Christmas tree" effect. I just need a way of starting the count from
>the start line, so I figured a wireless doorbell would be a cheap
>option, Wilkos sell them for under £5.
>Im planning to hook the output up to the reset pin of the 4017 to
>start the sequence. Maybe leave the first couple of outputs unused
>to allow for any false starts due to the chime pattern of the doorbell.
>Hope Im making sense now, I realise my first question was a little vague.

OK, understood. It should be straightforward to get a +ve going signal
for the 4017 reset pin by adapting one of those two methods I
illustrated. Details depend on what doorbell you have, as that will
determine the power supply arrangements and of course the duration of
its original chime signal. For example, if it's of the second type,
simply inverting the 4s output (with say a transistor or a spare logic
gate) would be sufficient, providing your Christmas Tree cycle time
was well over 4s, so that the long reset wouldn't matter.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Terry Pinnell, May 16, 2005
7. ### ChrisGuest

BoB wrote:
> Thanks for that Terry, I am building a set of starting lights
> for mini moto racing, im using a 555 and a 4017 to give
> the "Christmas tree" effect. I just need a way of starting the count

from
> the start line, so I figured a wireless doorbell would be a cheap
> option, Wilkos sell them for under £5.
> Im planning to hook the output up to the reset pin of the 4017 to
> start the sequence. Maybe leave the first couple of outputs unused
> to allow for any false starts due to the chime pattern of the

doorbell.
> Hope Im making sense now, I realise my first question was a little

vague.
>
> Bob

Hi, Bob. There have been a few questions recently about using these
cheapie wireless doorbells for remote control. I happened to have one
around, so I took it apart to see what's inside. And if yours is like
mine, you can do your circuit fairly easily.

I've got a "Dimango by Lamson Home Products", Model 3110R. The
coil and some discretes and transistors for the analog front end, with
a CMOS 4069 in the front end, too. This goes to a C.O.B. (Chip on
Board) PIC or other cheapie microcontroller (uC) mounted on a separate
small circuit board soldered to the main board. As far as I can see,
there's only one output from the uC -- the one going to the dinger.
That's a small 8 ohm 1/4 watt speaker.

When you're looking at interface, many times you don't have to have
Yoda-like understanding of the entire circuit -- just the part that
you're working with. I tracked down the circuit board traces and came
up with this for the output (view in fixed font or Notepad):

` VCC
` +
` |
` |
` | __ /|
` '--| | |
` .--|__| |
` | \|
` | 8 ohm
` COB ___ |/ 1/4 watt
` o-----|___|--|
` Output R |>
` |
` |
` ===
` GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

Well, that's something we can use. You know that with a 3V power
source, you'll probably get at least 2V square wave across the speaker
when the doorbell output transistor is on (transistor saturation and/or
battery voltage drop will keep the transistor from going fully on).
Now we're getting somewhere. We know it won't hurt the anything to
replace the speaker with a 1K resistive load like it shows in Mr.
Pinnell's link (you don't need the bell sound, anyway), and we can use
that voltage drop across the resistor to interface to the digital stuff
with another transistor:

VCC
+
|
.-.
| |
1K| |
'-'
|
|
o--->
| Logic Level Signal
|
|
|
|
___ |/ 2N
o----o------|___|--| 3904
From | 3.3K |>
Door .-. |
Bell | | |
Spkr | |1K |
Drive '-' |
| |
o----o ===
| GND
===
GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

At this point, if you can program a PIC, you're almost home. You can
ignore the several seconds of pulses which follow the start of the
doorbell ring, and start your sequence. Since you can get 20mA out of
a single output pin as long as you don't exceed 40mA per port, you can
drive the LEDs directly (with a current-limiting resistor), with one
input pin and 6 output LEDs (5 amber, one green). If you wanted to be
really crafty, you could just replace the speaker with a 100 ohm
resistor, use the two battery power supply for the PIC and forget the
level-shifting transistor.

But your post suggests you want to do this with 555s and a 4017, which
leads me to believe you don't have that capability. Doing this with
digital logic ICs, you're going to have some issues. The biggest one
is that the transistor will be turning the speaker on and off for
several seconds. It's a square wave, right? You want to have a single
pulse which starts when you press the button. So, you can use the
transistor pulse to trigger a 555 to a single pulse longer than the
time the doorbell is sounding (let's be generous and say 10 seconds).

VCC VCC VCC VCC
+ + + +
| | | |
.-. .-. | |
| | | |150K | |
1K| | | | | |
'-' '-' | |
| | .---o-----o---.
| | | 8 4 |
o----------)----o 2 |
| | | | A
| | | 3 o----->
| o----o 6 |
| | | LM555 |
| | | |
___ |/ 2N o----o 7 |
o----o------|___|--| 3904 +| | |
From | 3.3K |> --- | |
Door .-. | 100uF --- | 1 5 |
Bell | | | | '---o-----o---'
Spkr | |1K | | |
Drive '-' | | |
| | | |
o----o === === ===
| GND GND GND
===
GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

Now you have to look at some details. Your 555 has a positive-going
pulse when it's turned on, but the 4017 requires an active low (the
reset input to the 4017 is valid for a "1" input). So, you can use
another transistor to invert the logic. You need another 555 to count
down the Christmas Tree, and you can use the terminal count ("6" below)
to put CLKEN (clock enable) high, which inhibits counting. That will
mean the green LED will stay on until the first 555 goes off. Here's
The rest of the circuit (again, view in fixed font or Notepad):

VCC
+
A >---------------o--------. |
| | .-.
VCC | | | |4.7K
+ | | | |
| | .-. '-'
.-. VCC | 47K| | |
R1| | + | | | o-----.
| | | | '-' | |
'-' .---o----o---. | |/ |
| | 8 4 | '----| |
| | | |> |
o-----o 7 | | | VCC
| | | | | + .----------.
.-. | | === | | | |
R2| | | 555 | GND | | | |
| | .--o 6 | | | | |
'-' | | | .--------o-----o------o-------. |
| | | | | RST Vdd CLKEN | |
o--o--o 2 3 o--------o CLK | |
+| | | | 4017 | |
C --- | 1 5 | | | |
--- '---o----o---' .--oVss | |
| | N.C. | | "0" "1" "2" "3" "4" "5" "6" | |
=== === | '--o---o---o---o---o---o---o--' |
GND GND === | | | | | | |
GND | | | | | o-----'
| | | | | |
10K.-. .-. .-. .-. .-. .-.
all| | | | | | | | | | | |
| | | | | | | | | | | |
'-' '-' '-' '-' '-' '-'
| | | | | |
v v v v v v

VCC
+
|
|
V ~ Amber
- ~(Green)
|
|
.-.
| |
| |R5
'-'
|
From 4017 & |
10K Res. |/
>---o----| 2N3904

| |>
.-. |
10K| | |
| | |
'-' |
| |
=== ===
GND GND
(created by AACircuit v1.28.5 beta 02/06/05 www.tech-chat.de)

Note that each of the 4017 outputs also goes to a transistor as shown,
with the terminal "6" driving a green LED instead of an amber one.
I've left the choice of resistor values to you depending on what kind
of power supply you use and what kind of timing you'd like. For a 5VDC
supply and 1 second Christmas Tree timing, you might want to try 470K
for R1 and R2, 10uF for C, and 220 ohms for the 6 ea. R5. I'd
recommend against using the 3VDC of the receiver for the rest of the
circuit -- it won't interface properly here -- use the external,
regulated supply.

So, about 1 second after you press the doorbell transmitter, the amber
"1" will light up, 1 second later the "2" will light up, and so on. 5
seconds after doorbell press, the green "6" will light up, and stay on
for however long the 1st 555 is on (about 10 seconds above). That's
because the "6" is also driving CLKEN. As long as that's low, the 4017
will clock. When it goes high, the 4017 will stop clocking no matter
what's going on at CLK. But after 10 seconds, the 1st 555 will go off.
At that time, the 4017 will be forced into reset and all the lights
will go off until you press the transmitter button again.

If you don't want to use LEDs, you might want to use the transistor
outputs to drive other transistors, small relays, or use logic level
TO-92 triacs to drive a low voltage AC bulb. Your call.

Try this circuit out as it stands, though, and see if it works. Feel
free to post again if you've got other questions.

Good luck
Chris

Chris, May 16, 2005