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Pager triggering external alarm

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FiremanSam

New Member
Hi all,

I am struggling with a current project due to my current electronics knowledge being limited to the words electric and solder.

I basically need to wire up a pager to an external, louder alarm/siren as it only gets reception in one part of my flat and I am normally in another room with music/tv on.

I played around with sound sensitive designs but all the circuit kits I bought I must have soldered to death as they didn't work, and wiring up a microphone and just amplifying the sound picked up alot of environmental noise.

I have since got a spare pager and have opened it up, removed the vibration device and tried to create a circuit. The external siren I have needs mains power to run, so I got one of those multi-connection adaptors, spliced into it and had the power running into the pager where the vibration device was, back out to the siren and the from the siren back to the power to complete the circuit.

This worked fine when I tested it but I have since noticed that if the power is on then the pager doesn't get reception (tested with another one placed next to it).

I assume this is due to the amount of power flowing through the pager? (The pager runs of AAA battery and the minumum I can drop the adaptor down to is 4v).

So i figured that if I could wire up a circuit for the power and siren, and have it broken by a relay which is only triggered when the pager gets a message, this would isolate the power from the pager.

However, the two relay's I have used don't seem to be triggered by the pager. Not sure if this is a power issue? Perhaps the output the the pager would send to the vibration device is very small?

Can anyone help me resolve this or help me find a relay that can be triggered by low power (if this idea will actually work!)


Thanks in advance.

Jon
 

RadioRon

Well-Known Member
I didn't quite follow how you did your first hookup, but the second version seems to make sense. A relay is the obvious way to put it all together as you are doing. Most relays need a fair bit of power on their coil and I think you are right that the pager just can't provide it.

I am going to guess that the pager is powering the little vibrator motor inside at 1.5 volts, and the vibrator takes about 30 mA or so. Relays are made to run off all kinds of voltages so the ones you have could be for 6V or 12V or 24V or who knows what. Do they have part numbers on them? I can suggest two approaches. One is to buy a more suitable relay, but relays that operate from low voltage at low current are a bit exotic. Second approach is to use a circuit between the pager and the relay. Its best if we know first what the relay coil rating is, so we need that part number or perhaps if the relay coil voltage is written on the relay, tell us that.

The circuit will probably need one or two resistors and one or two transistors to create a switch in line with the relay coil. We'll identify the part numbers for each once we know about your relays.
 
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FiremanSam

New Member
Hi Radio Ron,

Thank you so much for taking the time to answer. With regard to the relay's - the ones I had were from a kit circuit from Maplin and don't have a particular number on them. I can take a photo if needed, but I am more then happy to purchase whichever particular one you suggest along with anything else I would need to make the other circuit between the pager and relay.

I look forward to your response.

Thanks again

Jon
 

Menticol

Active Member
Here it is!

I assume you can understand the required materials shown on the drawing, if not just ask.

Remove the electric motor and connect the circuit in its place, as shown
Do not modify anything else on the beeper

Obviously keep the AAA battery of the beeper, the 12V battery is only to power the relay

I suggest you to use a switch to mute the siren, in case your beeper goes crazy

Hope it helps!
 

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RadioRon

Well-Known Member
Menticol's circuit is the right idea. I think he may have missed putting a current limiting resistor on the base of that transistor, say a 39 ohm 1/4 watt type. We don't know what the source resistance from the pager is, so I would recommend this resistor to keep from damaging anything.
 

FiremanSam

New Member
Hi, just viewing this on the road so haven't got enough time to sit down and look at it at length at the moment, but just wanted to post and say thankyou for taking the time to actually respond and do a drawing.

I will look at it later and post back if I need help with the diagram.


Thanks again!

Jon
 
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