Hack a Wireless Doorbell Into Remote Switch

For some time I wanted to build a remote switch, main purpose – for firework ignition (or similar tasks). However, I wanted to create a RF remote without the use of microcontrollers, if possible to modify an existing device to do such a task.

Only one channel required (on/off state). Receiver device, after receiving a signal from the remote, should be able to stay on for a few seconds. Minimum distance required is 20m in the open space.

While searching over the internet, and came across a forum site, (http://www.elitesecurity.org/t373470 (forum is on the Serbian)) where I found schematics for hacking a doorbell, so I wanted to try it out. This setup seemed to me simple and easy to do. Some changes to the schematics are needed for this circuit to be fully functional.

Important note

Caution required when device is used in densely populated areas. Depending on the model of the wireless bell, it has a working frequency of 315 MHz or 433 MHz, it is certainly possible that other device that operates on the same frequency could trigger the device (Because of this, I used this device for firework ignition outdoors away from houses). As it lacks some safety issues the greatest use of it would be to use it to (harmlessly) prank your friends

Again, you are responsible for yourself and your actions.

Step 1: Materials and Tools Needed

Materials needed:

1x cheap Chinese wireless doorbell (with transmitter and receiver included)

1x LED

1x diode 1n4001

1x 100µF electrolytic capacitor

1x 470 Ω resistor

1x BD681 darlington transistor

1x relay 5v

1x old 9 volt battery (or old 9v battery clip)

1x new 9v battery

Wires

Heat shrink tube or insulating tape

Batteries for receiver - depends on the model

Tools:

Screwdriver

Pliers

Scalpel

Soldering equipment

Multimeter – optional

Step 2:

First open the receiver, unscrew any screws and carefully open case. Batteries and receiver are connected to one part of the case; however the speaker is probably connected to the other part. Be careful not to tear any wire.

Connect, and solder negative terminal of the receiver (ground) with wire (which will be connected to the negative terminal of 9v battery, later).

Cut the wires that are connected to the speaker. Speaker is no longer needed; it can be removed from the case.

Following schematics connect LED across free speaker terminals. A multimeter can be used to find a positive terminal, although I found that polarity changes over both terminals so, at this point do not worry about polarity.

Next, connect a diode (mine was 1n4001) to the one of the terminals (see schematics).

Step 3:

Time to place a 100µF electrolytic capacitor. Just watch polarity! Without the capacitor, finished device will create relay that ‘sing’ doorbell melodies, and be barely useful.

The capacitor role here is to store some charge received from the speaker terminals, and slowly discharge through darlington transistor, creating more smoother performance.

At least 10µF is needed to smooth signal received from speaker terminals, however upper limit don’t exist, so you could hook a 1000µF or higher value capacitor and it will work fine, and it will extend the ON state of the device, after a signal from speaker disappear.

Connect 470 Ω resistor, and base of BD681 darlington transistor. Connect the emitter to the negative (ground) wire. Watch the pin-out of the transistor. Download data-sheet if needed.

(I’m not sure if regular npn transistor can be used in this setup.)

Now solder a wire to collector of the BD681, and the other end of wire solder to one of the 5v terminals of the relay. *Decide how much wire length you needed.

Solder the second wire to the relay.

Now a 9volt battery clip is needed. It can be made from an old 9v battery; instructions for this can be found here: https://www.instructables.com/id/quick-cheap-9V-ba...

https://www.instructables.com/id/9V-battery-clip-fr...

Now solder a free wire from the relay to the positive terminal of battery clip, and negative terminal to the wire that is connected to the negative (ground) of the receiver.

Insulate terminals with tape or shrink tube, close box, put in the batteries.

And it’s done.

Step 4: Testing

For first test connect 9v battery, make some distance press the remote and with LED turned ON relay should switch (you should hear the sound).

After pressing a remote button, relay switches ON for about 3 -10 seconds (depending on the bell melody). Device cannot work continuously, but it is well suited for use as a very simple firework ignition (and many more).

Thanks for viewing!

Comments

[PirateKing08]

This idea worked great to switch my old 12v doorbell. I used the Byron wireless receiver but it eats batteries! So I have tried to do the same trick with the mains Byron version. The same speaker wires now connect to the speaker in the mains version and common ground i soldered to ground plane of pcb inside mains receiver. I left the speaker still connected so i could hear i hadnt damaged receiver when put back together. When i press bell switch LED flashes and receiver speaker makes bell sound but 12v bell is not sounding anymore. Relay battery is still 9v. I am assuming the darlington is not switching relay. It worked with previous battery receiver. Is my ground from the mains receiver pcb not allowing a vbe across the darlington ? Or by leaving the speaker still in place means not enough base current for the darlington?

[Pustolov]

Hi, PirateKing08
You could try removing the speaker to get more power in the darlington, try also some smaller cap (1 - 10uF). Or maybe 9v battery doesn't have enough power to switch 12v dorbell.
Either way, try experimenting a bit, as long as the critical voltage values are not exceeded, everything should be fine with circuit.

[BryanL115]

I have a hard wired old doorbell in my old house The wires for the switches are broke off inside the brick fasad. I'm lookin for a wireless doorbell kit that I can modify to ring the hard wired chimes

[Pustolov]

Well, it is kinda tricky, but I think it's possible to connect the old bell to wireless doorbell. The problem is the voltage of the old bell power supply, also without knowing the scheme of an existing doorbell, It's hard for me to give you the right answer.

[PirateKing08]

I used this wireless switch to turn my old 12v wired doorbell into a wireless doorbell as the old bell wire was broken during porch replacement. Works great although the cap is a bit too big as the "bong" comes a long time after the "bing"

[BryanL115]

Thanks any body want to attempt this for$

[BryanL115]

all the wireless chime would have to do is close the circuit to make old chime ring ie old style doorbell switch

[Pustolov]

Then, You should follow this instructable and connect your doorbell to the relay.

[CuspissN]

Not a good idea to use for fireworks or anything that could be dangerous if faultsly triggered. I've seen these door bells triggered by neighboring garage door openers. Many devices share the same frequency.

[Pustolov]

I agree with you, but in my surroundings there is nothing that could
trigger the device, so no one's safety was threatened.

But your comment is in place, it is certainly possible that other device
that operates on the same frequency start the device.

[BeachsideHank]

Adding an optional latching circuit for continuous on would make this hack just a bit handier for more applications like remote switching of dust collectors, etc. Still though, nice hack even in it's present form.

[CuspissN]

A latching relay may be a way to go.

[Pustolov]

A good proposal;

then, ignore the signal which coming into the speaker and connect latching circuit directly to the pin
on the receiver that creates a signal when button is pressed. As you said
it would a bit handier for more applications like remote
switching.

(I just wanted to create a radio remote to impress some kids from my
neighborhood, (for the Orthodox New Year), so as a date for the
holiday was very near, I had to find a way to create remote very fast, and it
works fine for that purpose)

[dani_a_z]

great instructble !!!
????
and perhaps you can use the remote switch to make a wireless door lock

Check out this awesome Instructable.

https://www.instructables.com/id/Wireless-Door-Unloker-System

[Pustolov]

Interesting, but I think it would need additional modifications so that wireless
bell could perform as a wireless door lock.

Your instructable seem much more suited for that purpose.

[dani_a_z]

www.instructables.com/id/Wireless-Door-Unloker-System