Need help with drive alert circuit

Thread Starter

Ntmike

Joined Apr 3, 2020
45
Hello all. I bought a drive way alert system skylink. i like this alert set, but this system only turn on a buzzer when activated. I would like for it to turn on a 12v relay to power my 12v lights But the power that the buzzer on , need some kind of modification to turn the 12v relay on. Please help me with this. Thank you.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
Is it like this one?
https://www.amazon.com/Skylink-HA-300-Household-Business-Security/dp/B00EUWAI9M

Are you skilled enough to open the unit and hack into the circuit board after measuring some voltages?

There's a solution that does not require altering the unit: You would use a device that is activated by the sound of the alarm. That would be my last resort but it is an option.
Thank you very much for your reply. Yes, that is the unit. Do you know which device that I could use and it activate by this unit buzzer alarm? I have tried to wired the relay to the led terminal of the unit. It turn on my relay and lighting but somehow created a limit on the wireless sensor to reciever about 20 ft.
 

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wayneh

Joined Sep 9, 2010
16,384
I have tried to wired the relay to the led terminal of the unit. It turn on my relay and lighting but somehow created a limit on the wireless sensor to reciever about 20 ft.
That sounds like the relay took too much power and interfered with the reception. You could likely solve this by using a transistor to drive your relay instead of powering it directly off the LED signal. One pole of the relay coil would go to +12V from the power supply, the other to the collector of the transistor. The emitter of the transistor to ground. Activate the base of the transistor with the LED signal, with a 1kΩ resistor in between. This all assumes an NPN BJT. You could use a MOSFET instead.

If the power supply to the device is not enough to power your relay, you may need to find one with a higher rating.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
That sounds like the relay took too much power and interfered with the reception. You could likely solve this by using a transistor to drive your relay instead of powering it directly off the LED signal. One pole of the relay coil would go to +12V from the power supply, the other to the collector of the transistor. The emitter of the transistor to ground. Activate the base of the transistor with the LED signal, with a 1kΩ resistor in between. This all assumes an NPN BJT. You could use a MOSFET instead.

If the power supply to the device is not enough to power your relay, you may need to find one with a higher rating.
Thank you. I will try that and i hope that it would work. Thanks
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
That sounds like the relay took too much power and interfered with the reception. You could likely solve this by using a transistor to drive your relay instead of powering it directly off the LED signal. One pole of the relay coil would go to +12V from the power supply, the other to the collector of the transistor. The emitter of the transistor to ground. Activate the base of the transistor with the LED signal, with a 1kΩ resistor in between. This all assumes an NPN BJT. You could use a MOSFET instead.

If the power supply to the device is not enough to power your relay, you may need to find one with a higher rating.
Thank you. I will try that and hope that it would work. Th
That sounds like the relay took too much power and interfered with the reception. You could likely solve this by using a transistor to drive your relay instead of powering it directly off the LED signal. One pole of the relay coil would go to +12V from the power supply, the other to the collector of the transistor. The emitter of the transistor to ground. Activate the base of the transistor with the LED signal, with a 1kΩ resistor in between. This all assumes an NPN BJT. You could use a MOSFET instead.

If the power supply to the device is not enough to power your relay, you may need to find one with a higher rating.
The led have a constant 3.6v on both terminals. When alarm activated one terminal drop to zero volt becomes ground(this is the one I grounded the relay before) I have tried your procedure it turn the relay on right away without alarm on. Is there another way?
 

ebeowulf17

Joined Aug 12, 2014
3,274
Thank you. I will try that and hope that it would work. Th

The led have a constant 3.6v on both terminals. When alarm activated one terminal drop to zero volt becomes ground(this is the one I grounded the relay before) I have tried your procedure it turn the relay on right away without alarm on. Is there another way?
Sounds like you're halfway there - you just need to add a second NPN transistor (and a few resistors) to invert the signal.

You could do a simple test to make sure all you need is the signal inversion and that everything else is ok. Power the system back up like you had it before - you say the relay is powered immediately, with no alarm signal. Now trigger the alarm; does the relay turn off at that point? If so, all you need is the logic inversion. If not, there's some other wiring problem.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
Sounds like you're halfway there - you just need to add a second NPN transistor (and a few resistors) to invert the signal.

You could do a simple test to make sure all you need is the signal inversion and that everything else is ok. Power the system back up like you had it before - you say the relay is powered immediately, with no alarm signal. Now trigger the alarm; does the relay turn off at that point? If so, all you need is the logic inversion. If not, there's some other wiring problem.
Yes sir, power the unit on the relay on. When alarm activate the relay off. It works opposite. What can i do to make relay on only when alarm on
 

ebeowulf17

Joined Aug 12, 2014
3,274
Yes sir, power the unit on the relay on. When alarm activate the relay off. It works opposite. What can i do to make relay on only when alarm on
I think you just need one more transistor and one more resistor. See the attached schematic. Note that the LED will have current running through it at all times. It will be dimmer when alarm is off, and brighter when it's on, but the LED will never go totally dark because of current running through it and the transistor base-emitter junction.
AAC-LED-drive-relay-02.PNG
 

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Thread Starter

Ntmike

Joined Apr 3, 2020
45
I think you just need one more transistor and one more resistor. See the attached schematic. Note that the LED will have current running through it at all times. It will be dimmer when alarm is off, and brighter when it's on, but the LED will never go totally dark because of current running through it and the transistor base-emitter junction.
View attachment 203564
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
Is there away to extend the the relay on time Relay only kick on for 22 seconds then go off when led go dim even though the alarm still on for about another 3 minutes?
 

ebeowulf17

Joined Aug 12, 2014
3,274
Is there away to extend the the relay on time Relay only kick on for 22 seconds then go off when led go dim even though the alarm still on for about another 3 minutes?
I'm not sure. That's interesting behavior.

Before you made any notifications to the circuit, with no external parts connected, did the LED state change after around 22 seconds and buzzer went for another 3 minutes? Or is this change something new, that's only happening because of the addition of external components?
 

wayneh

Joined Sep 9, 2010
16,384
Is there away to extend the the relay on time Relay only kick on for 22 seconds then go off when led go dim even though the alarm still on for about another 3 minutes?
Holding something on for a period of time is a classic application for a 555 timer circuit called a one-shot. It won't trigger again until the alarm resets.
 

Thread Starter

Ntmike

Joined Apr 3, 2020
45
I'm not sure. That's interesting behavior.

Before you made any notifications to the circuit, with no external parts connected, did the LED state change after around 22 seconds and buzzer went for another 3 minutes? Or is this change something new, that's only happening because of the addition of external components?
The led design that way. It only on for 22 seconds than dim away
 

ebeowulf17

Joined Aug 12, 2014
3,274
The led design that way. It only on for 22 seconds than dim away
I'd agree with @wayneh then. A 555 timer is probably the easiest solution if you need the relay to be active longer than the LED.

I suppose the other possibility would be tapping into the buzzer circuit, but it might be tricky to find the right spot in the circuit to tap into to get a clean, sustained signal. The signal at the speaker itself is almost certainly some sort of AC signal which would be trickier to convert into a relay control.

Do you want the relay to be on the exact same length of time as the buzzer, or is it ok for the relay timing to be a little different?
 
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