Wireless doorbell switch

Hi

Is it possible to convert the output of a wireless

Doorbell to power a small relay or switch?

Thanks in advance

Bob

Reply to
BoB
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Here are examples of two simple circuits I've used to do that:

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--
Terry Pinnell
Hobbyist, West Sussex, UK
Reply to
Terry Pinnell

One day BoB got dressed and committed to text

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

Reply to
Rheilly Phoull

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.

Hope this is a better answer than "Sorry, we need more information." :-)

Good Luck! Rich

Reply to
Rich Grise

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

Reply to
BoB

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
Reply to
Terry Pinnell

from

doorbell.

vague.

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 receiver is powered by 2 AA batteries, which gives 3VDC. There is a 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 |>

` | ` | ` =3D=3D=3D ` GND (created by AACircuit v1.28.5 beta 02/06/05

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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 =3D=3D=3D | GND =3D=3D=3D GND (created by AACircuit v1.28.5 beta 02/06/05

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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 =3D=3D=3D =3D=3D=3D =3D=3D=3D | GND GND GND =3D=3D=3D GND (created by AACircuit v1.28.5 beta 02/06/05

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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 | | | | | + .----------. .-. | | =3D=3D=3D | | | | 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" | | =3D=3D=3D =3D=3D=3D | '--o---o---o---o---o---o---= o--' | GND GND =3D=3D=3D | | | | | | | GND | | | | | o-----' | | | | | | 10K.-. .-. .-. .-. .-. .-. all| | | | | | | | | | | | | | | | | | | | | | | | '-' '-' '-' '-' '-' '-' | | | | | | v v v v v v

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

.-. | 10K| | | | | | '-' | | | =3D=3D=3D =3D=3D=3D GND GND (created by AACircuit v1.28.5 beta 02/06/05

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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

Reply to
Chris

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