Hello I'm new to this forum hope I landed in the correct forum

I have a thermo sensor which monitors several freezers temperature
When temperature is out of bounds it emmits a continuous fixed frequency beep. Its not smart home sensor but old style one.

The beep is not loud (I guess some small piazo buzzer) and cannot be heard if I'm not in vicinity or not at home

What I would want is to attach externally to the thermo sensor a small circuit with a tiny microphone that can trigger ,based on the beeping sound, a small dry contact relay that I can connect to my smart home system as input trigger. This circuit should somehow avoid environmental noise if possible

If anyone can help how to design such a circuit or built something simiar and can share

Thanks

 

https://quasarelectronics.co.uk/Item/3126-sound-activated-relay-switch

Any good?

 

https://quasarelectronics.co.uk/Item/3126-sound-activated-relay-switch

Any good?

Thanks
I have seen these kind of circuits
But can they be programmed to respond to certain frequency range, not sure it will work if it will respond to just any noise

 

Thanks
I have seen these kind of circuits
But can they be programmed to respond to certain frequency range, not sure it will work if it will respond to just any noise

A simple solution would be to feed the sound signal to a LM567 (or NE567) tone decoder IC that will detect just the frequency you need

 

A simple solution would be to feed the sound signal to a LM567 (or NE567) tone decoder IC that will detect just the frequency you need

Thanks
Can you suggest a circuit with LM567 ,and does it connect with small microphone

 

Thanks
Can you suggest a circuit with LM567 ,and does it connect with small microphone

Hello, yes, we would need the frequency of the tone that needs to be detected though to calculate the R/C components

This board may do the trick:
https://www.electrodragon.com/product/special-sound-identifier-module/

 

A simple solution would be to feed the sound signal to a LM567 (or NE567) tone decoder IC that will detect just the frequency you need

That is a seriously old-school suggestion. Gotta love it.

This board may do the trick:
https://www.electrodragon.com/product/special-sound-identifier-module/

GREAT find. The output can sink 100 mA, way more than enough to drive a small reed relay. Don't forget a suppression diode across the coil. 1N914, 1N4148, etc.

ak

 

Do you have the relay already, or are you looking for suggestions? If the latter, do you know the open-circuit voltage and closed-circuit current (or input impedance, or whatever) of what is being switched?

ak

 

Hello I'm new to this forum hope I landed in the correct forum

I have a thermo sensor which monitors several freezers temperature
When temperature is out of bounds it emmits a continuous fixed frequency beep. Its not smart home sensor but old style one.

The beep is not loud (I guess some small piazo buzzer) and cannot be heard if I'm not in vicinity or not at home

What I would want is to attach externally to the thermo sensor a small circuit with a tiny microphone that can trigger ,based on the beeping sound, a small dry contact relay that I can connect to my smart home system as input trigger. This circuit should somehow avoid environmental noise if possible

If anyone can help how to design such a circuit or built something simiar and can share

Thanks

Can you not tap across the buzzer output driver , and use it to drive a slave transistor relay?

Any pictures of the circuit board .