Electronics - can you buy a "sticky relay"?
Discussion
For long and boring reasons I need to wirelessly activate a wired doorbell.
I've opened up the wireless doorbell receiver we have and there are a few LEDs in there which flash a few times when the doorbell is pushed so I was thinking I could attach a relay to one of those to detect a voltage, the other contacts for the relay would be connected to the wired doorbell switch so when the LED flashes the wired doorbell chimes.
In my head I don't see why this wouldn't work, but the last time I did anything with electronics was 20 years ago in A-level physics so I could be way out.
Also, the LEDs flash a few times so I'm hoping there exists some kind of relay that sticks for half a second or so when the LEDs flash the relay is on for a pulse, then off as if the wired doorbell chimed at the rate the LEDs flash it could sound a bit nuts! The doorbell dings when there's a circuit, then dongs when the circuit is broken.
Can anyone point to what kind of relay I need to be looking for? The LEDs seem to be about 2V and the doorbell switch circuit is 8V.
I've opened up the wireless doorbell receiver we have and there are a few LEDs in there which flash a few times when the doorbell is pushed so I was thinking I could attach a relay to one of those to detect a voltage, the other contacts for the relay would be connected to the wired doorbell switch so when the LED flashes the wired doorbell chimes.
In my head I don't see why this wouldn't work, but the last time I did anything with electronics was 20 years ago in A-level physics so I could be way out.
Also, the LEDs flash a few times so I'm hoping there exists some kind of relay that sticks for half a second or so when the LEDs flash the relay is on for a pulse, then off as if the wired doorbell chimed at the rate the LEDs flash it could sound a bit nuts! The doorbell dings when there's a circuit, then dongs when the circuit is broken.
Can anyone point to what kind of relay I need to be looking for? The LEDs seem to be about 2V and the doorbell switch circuit is 8V.
You would likely not be able to “power” the relay from the LED circuit as you’ll draw way too much current.
You would need a transistor to switch the relay, with the LED trigger on the base.
Once you’re into building a circuit to do it - then the delay could be built in too to make the relay “sticky” - but sounds like this maybe a little OTT for this application.
You would need a transistor to switch the relay, with the LED trigger on the base.
Once you’re into building a circuit to do it - then the delay could be built in too to make the relay “sticky” - but sounds like this maybe a little OTT for this application.
What you are describing is a monostable (if I get it) - defaults to a state (say off), kick it and it temporarily flips to the other state (say on). The temporary time is settable.
There are standard logic ICs (e.g. 555, 74xx121 or 4098) which do this and which can work with the voltages you describe. And can be low power.
You may need a transistor to drive your doorbell dependent on its drive.
There are standard logic ICs (e.g. 555, 74xx121 or 4098) which do this and which can work with the voltages you describe. And can be low power.
You may need a transistor to drive your doorbell dependent on its drive.
As a start , look at opto couplers, driven from the drive for the LEDs. One common type is a 4N25 (data sheet is available as a download) . There's a drawing on most data sheets showing it's configuration. Basicly the input is a LED, where the input current is controlled by a series resistor ( value determined by deducting the average forward drop from the LED drive voltage to keep the Opto input current low and the output current is determined by the output external resistor which could be high as the 555 only needs a voltage of 2/3 of the supply voltage to trigger. Couple that to a 555 circuit ( connected to the output of the 555/output resistor ) (https://www.mitchelectronics.co.uk/product/555-monostable/ gives a few variations ) .
Only problem is that a 555 needs 5-16v to operate. If you want to be really inventive, you could add a second 555 controlling the first to stop the door bell pushers and only let the bell ring a second time after a set time .
Only problem is that a 555 needs 5-16v to operate. If you want to be really inventive, you could add a second 555 controlling the first to stop the door bell pushers and only let the bell ring a second time after a set time .
Penelope Stopit said:
Have you possibly using a complicated method?
Wired button when pressed closes a circuit (this is what you have now)
A transmitter button (remote control fob) will trigger a receiver that can switch a relay to close the wired button circuit
or
Am I missing something?
Yeah, that's exactly what I'm trying to do - we had a wired doorbell, had a new door fitted and we thought we'd just get a new wireless doorbell instead of drilling into the new frame to wire in the existing switch, we really didn't like the new doorbell sound so now I'm trying to get the old doorbell to work with the new button.Wired button when pressed closes a circuit (this is what you have now)
A transmitter button (remote control fob) will trigger a receiver that can switch a relay to close the wired button circuit
or
Am I missing something?
This is what the insides of the wireless doorbell looks like -
The only place I can think of to trigger the relay is the LED and that flashes.
What you need is a momentary wireless remote control switch
Search ebay/Google there are plenty of them about
If you don't like any of the transmitters (buttons), remove the board from the one of your choice and install it into the case you already have, keeping the original cases button will be the challenge if you were to swap the remotes guts over from one to the other, you would need to epoxy the button in place and solder wires to it then connect those wires to the new remotes button circuit
Hopefully you will find a momentary wireless remote control switch of good enough appearance for the door frame
Search ebay/Google there are plenty of them about
If you don't like any of the transmitters (buttons), remove the board from the one of your choice and install it into the case you already have, keeping the original cases button will be the challenge if you were to swap the remotes guts over from one to the other, you would need to epoxy the button in place and solder wires to it then connect those wires to the new remotes button circuit
Hopefully you will find a momentary wireless remote control switch of good enough appearance for the door frame
It might be possible to take a signal from one of the traces / pins to use for something else - my starting point would be the trace / pins I've highlighted yellow - but there are a lot of "it depends" to conclude that fully.
As others have suggested, wiring old doorbell into new button (even though it might mean drilling through) or using a momentary remote on / off switch, would probably be overall easier.
Side note: for a "sticky relay", these days I'd use a PIC - they're little programmable microcontrollers, so the program would turn an output on for x seconds when an input signal was detected. Interface to whatever using transistor / darlington driver / opto-isolator.
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