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Total Newbie Question: Using a relay as a switch?

BaconCatBug

May 25, 2017
4
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May 25, 2017
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Hi all. Once again I have a complete newbie question here,.

I wear headphones and more often than not I cannot hear when someone is knocking at the door. I have a wireless doorbell that lights up a piddly little red LED for about 5 seconds to visually catch my attention but as it's so nondescript I often don't notice it. A lot of the equipment tailored towards the hard of hearing with lights and such are horrendously overpriced because they can get away with the pricing. Instead I am hoping it would be possible to cut out that LED and replace it with a relay which will light up a string of flashing battery powered multicoloured LEDs instead.

This is a crude image of what I was hoping to do: http://imgur.com/a/r64un

My actual question is what kind of relay should I use or should I be using something else? I guess I am looking for advice on what part exactly to get. Is it an SPNO or SPNC relay I would need?

Apologies in advance for the total newbieness.
 
Last edited:

Joosh

Feb 25, 2017
14
Joined
Feb 25, 2017
Messages
14
Hi all. Once again I have a complete newbie question here,.

I wear headphones and more often than not I cannot hear when someone is knocking at the door. I have a wireless doorbell that lights up a piddly little red LED for about 5 seconds to visually catch my attention but as it's so nondescript I often don't notice it. A lot of the equipment tailored towards the hard of hearing with lights and such are horrendously overpriced because they can get away with the pricing. Instead I am hoping it would be possible to cut out that LED and replace it with a relay which will light up a string of flashing battery powered multicoloured LEDs instead.

This is a crude image of what I was hoping to do: http://imgur.com/a/r64un

My actual question is what kind of relay should I use or should I be using something else? I guess I am looking for advice on what part exactly to get. Is it an SPNO or SPNC relay I would need?

Apologies in advance for the total newbieness.

I'm gonna say something like this may be useful to you: https://www.google.co.uk/search?q=relay+optocoupler+board

Low voltages. I'm assuming the doorbell circuit is battery powered too? Isolated doorbell from your flashing LED power supply. And cheap!

Most of them have NO and NC contacts so you can play about. Generally would use NO for your application - the flashing LEDs would be off until your doorbell circuit turns on the relay via the optocoupler.

Edit: You could just use one of those small blue relays on it's own if your doorbell circuit is capable of powering it.

Josh
 

duke37

Jan 9, 2011
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A junction transistor or MOSFET will be able to drive a more powerful light. A suitable power supply will be required.
 

Audioguru

Sep 24, 2016
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A red LED uses only 1.8V. The 12V relay needs at least 9V that your doorbell does not have.
The input to a transistor can behave exactly like the LED in the doorbell circuit but the bright lights it drives need an extra power source.
 

duke37

Jan 9, 2011
5,364
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It may do but will only drive 70mA.
It seems to be fussy with control voltage of 1 to 1.3V.
Decide on the light you wish to use, find its voltage and current requirements, find a power supply with ample spare capacity.
The switch can be a MOSFET, junction transistor (prefered) or Darlington. Plenty of choice, small and cheap.
 
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