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Old 26-02-2019, 10:18   #1
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multiple alarms to one set of buzzers - need circuit

I'm interested in combining alarms to one set of buzzers, as follows:

I have several different bilge pumps, each with a 'smart' switch, which will send 12volts to a buzzer.
I also have an alarm output from my vesper AIS

It's my understanding that I can rig up diodes in line with each SENDING alarm signal so that if one is activated, it doesn't back feed into the other signals.

I'm thinking in terms of a small panel with LEDs so that when I get an alarm, the buzzer goes off and the panel tells me which input caused the alert.

Can anyone advise me on what diodes to use?

Another nice to have would be some sort of latching relay, so that I can kill the buzzer, but it will reset when the alarm is over, ready for the next alarm to be audible.

Thanks,

Matt
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Old 26-02-2019, 23:34   #2
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Re: multiple alarms to one set of buzzers - need circuit

Paralleled SCR circuits will latch with a normally closed switch on the supply to the SCRs to unlatch and cancel the alarm.
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Old 26-02-2019, 23:57   #3
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Re: multiple alarms to one set of buzzers - need circuit

If the buzzer draws less than an amp, any 1A diode like a 1N4004 will do.

The latching relay will work, you need a relay with a single pole and normally closed and normally open contact with a common and a normally open momentary switch to use for temporary disabling. Only connect this to the buzzer and not the idiot lights, obviously.
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Old 27-02-2019, 13:29   #4
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Re: multiple alarms to one set of buzzers - need circuit

I'd also make sure to isolate the circuits - optocouplers would work well for this. You'll need to figure out what the trigger signal is on each alarm, then get the appropriate optocoupler to tie in (signal lights a light, photoresistor closes the circuit). Simple, cheap, no way for one signal to backfeed the other devices, no chance of forming a ground loop, and no current draw when not in use.
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Old 27-02-2019, 21:58   #5
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multiple alarms to one set of buzzers - need circuit

Forget buzzers. How about a unique voice announcement for each bilge pump and alarm? All in this package: https://www.elkproducts.com/product-...e-voice-module
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Old 27-02-2019, 22:09   #6
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Re: multiple alarms to one set of buzzers - need circuit

Before you go crazy making your own system, take a look at the alarm systems made by Aqualarm. They may have one that will do everything you need.
https://aqualarm.net/automatic-sys-m...304928d9f13719
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Old 27-02-2019, 23:43   #7
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Re: multiple alarms to one set of buzzers - need circuit

Try something like this. Note, your alarm inputs must be 0/12V (12V = ALARM) and provide enough current to drive the relay, the LED, and the buzzer. The relay and buzzer must be 12V. The relay and buzzer must draw well under 1A, otherwise you will need higher-current diodes.

You can add as many inputs as you like, just duplicate the LED, resistor, and diode. The LED will be drawing about 10mA. With high-efficiency LEDS, you can probably increase the resistor value to 4.7K and still have them plenty bright.

And yes, all alarm circuits must share a common ground.

The "MUTE" pushbutton latches the relay and disables the alarm. This circuit resets when all the alarms have cleared.
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Old 05-03-2019, 14:36   #8
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Re: multiple alarms to one set of buzzers - need circuit

Paul,

Your circuit diagram is exactly what I needed! - thank you, thank you, thank you.


Out of curiousity, what purpose to the resisters serve?

Matt
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Old 05-03-2019, 15:10   #9
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Re: multiple alarms to one set of buzzers - need circuit

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Originally Posted by mlydon View Post
Paul,

Your circuit diagram is exactly what I needed! - thank you, thank you, thank you.


Out of curiousity, what purpose to the resisters serve?

Matt

They stop the LED's burning out. LED's are pretty much the same as a regular diode and would otherwise short circuit if a current limiting resistor wasn't applied.


I'd probably just be inclined to use a pilot lamp instead for an occasional alarm indicator.
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Old 05-03-2019, 15:39   #10
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Re: multiple alarms to one set of buzzers - need circuit

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They stop the LED's burning out. LED's are pretty much the same as a regular diode and would otherwise short circuit if a current limiting resistor wasn't applied.


I'd probably just be inclined to use a pilot lamp instead for an occasional alarm indicator.
Yes, the resistors limit the LED current. I am assuming raw LEDs, not the ones with built-in limiting resistors. If you have LED lamps designed for 12V operation, then you don't need the resistors shown in my schematic.
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