Furuno radar buzzer mod

[markxengineerin]

Furuno Navnet vx2

The warning buzzer is annoying when I don't want to hear it, and not loud enough when I'm far away from the head unit.

I've taken it apart and located the buzzer, which is this:
https://www.jameco.com/Jameco/Produc...DS/2320375.pdf



Any reason why I can't snip this out, and replace it with jumper wires to a relay that takes less than 2V and 70mA to close? That way I can add external logic, lights, buzzers, etc.

(The external alarm output provided by Furuno doesn't help. I forget exactly why I didn't like it, but IIRC it did not sound off for the most important alarm (something in the radar safety zone). I think they set it up to work with the anchor alarm feature, maybe others, but wasn't working w/ the radar portion and I remember the user manual saying this was normal.)

[markxengineerin]

Relay I found



Direct replacement for the buzzer?

[river]

Are you sure that is the part? Very strange choice of 1.5V.


In any case, I would measure the voltage applied to the buzzer pins, and add a transistor to switch your relay, and diode for protection from back emf. You can then use a more common relay at whatever voltage is convenient.

[markxengineerin]

You're right, I'm not sure. I guess this could be a beeper for the keypad, like something that sounds when a button is pressed?

A more standard warning buzzer is here:
https://www.defender.com/product.jsp?id=744113#
That's .144 watts, vs. "<.105 watts" as best I can calculate for the dbx-12pn. dbx-12pn is 75db vs. 85db for Aqualarm.

I'll keep looking today for other buzzer looking things in there, thanks for making me question this. I was so thrilled to have found a buzzer at all that confirmation bias crept in quickly.

[markxengineerin]

I made a mistake on the part number, it's actually a 12V model, 85dB. That makes more sense.


This is a "passive buzzer" meaning it does not just buzz with 12VDC applied to it. It needs AC voltage near 2400hz to excite it. My plan now is to replace it with a 140 ohm resistor, and tap into the + and - pin, route the wires externally, for now.

Now, how to best detect a 12V signal at 2400hz, to trigger my new alarms, and without adding any significant resistance to the circuit?

[Be Free]

Way out of my area of expertise here, but wouldn't those extended wires become a source of RF noise with 2400Hz AC on them?

[markxengineerin]

I'm also out of my area, but it's only 12V, so hopefully not a noise issue. In retrospect I should have used a shield and twisted cable, but since this is mostly done, will try this first.

[river]

It's hard to design something to connect to that without more information about how the speaker was driven. I have attached something which should work in most cases, if the driver is as I guess it probably is. First though, check that the negative output for the speaker is grounded. If that is driven you don't want to short it to ground.


I would probably connect the power for this circuit to the radar, to take advantage of the surge protection it probably has in it.

[markxengineerin]

Hi river, thank you very much for taking a look at this. I confirmed that negative output is not grounded, there is about 20 MOhms of resistance (multimeter drifting around, not steady reading). I will study your circuit in more detail and will probably have some more questions.

[smac999]

I highly doubt it's putting a freq signal into the buzzer. the 2400hz is probably the sound tone. when 12v dc is applied

[river]

Ok, so they probably have a transistor amplifier on the low side, so this circuit would need to be flipped around to work on the high side. You could also check if the positive output is connected to 12V, and measure voltage across the output when it is active. Also check if it is actually just a 12v output, and not modulated, then would not need so many components, but it would work anyway.

[markxengineerin]

The thing that makes me think it is a passive buzzer (will not sound on steady 12VDC) is that they call it a "transducer", which from my reading is a word used for passive buzzers. I have sent the company an inquiry to check, as it will be some time before my radar is wired up again and possible to turn on.

When I had it apart, I tried it using a 1.5VDC battery, and it made no sound, but didn't think at the time to try 12V, as I had read the part number wrong.

[markxengineerin]

From the manufacturer:
This is an electromechanical "transducer."
It requires an external, 0-peak signal at your desired frequency -- 2400Hz being the resonant frequency.
It supports 6V to 15V.

[markxengineerin]

Here is what happens when it's buzzing:
https://youtube.com/shorts/yRA7HeNsABs?feature=share

If any EE's still following, does this change anything about the proposed circuit above? I do not have an oscilloscope to do a better job measuring it right now, but might get a cheap one if it will help.

[markxengineerin]

Coming back to this project: Rather than trigger a relay directly, I would like to sense the buzzer with an Arduino, so that I have more options on how to interpret the alarm and what actions to take. The easiest/least invasive way I can think of is to put a microphone right next to the buzzer. This one has a digital output that switches at an adjustable sound threshold:
https://www.mpja.com/Analog-Sound-Se...info/35077+MP/
And as a bonus, the company is walking distance from Riviera Beach, my next destination. As long as I can find the right distance between the buzzer and the this module, and set a threshold high enough that nothing else triggers it very often, I think it will work (?)