I have heard there is a unit that will detect fire and police and light an LED for deaf drives.. I have googled all over. Nothing. I think US sirens are in the 1-2Khz range.

Has anyone done anything like this or have a circuit similar. I want to mount a mic outside the car, and light an LED in the car, direction is not important.

I am weak in analog/filters. And I know some of you guys will spice it in seconds. I can get more details if needed. It would be nice it all discretes over
an op-amp as well, but begger can't be choosers.

Thanks.

 

Filters are fairly easy to constuct. just remember that a coil in series with a capacitor allows the frequency your interesred in to pass through, and a parallel one rejects it. So you build a Pi filter with this in mind. Two parallel circuits connected together with a series circuit.

 

So a low pass then a high pass of coils and caps.. Will do search for that. I recall knotch filters and bandpass, but that is in 1979, but I do still have the old lab notes in the attic I am sure. I will attempt to load a circuit lab and simulate it first. I want to use a transistor as the output as well, so not op amp to solder or buy..

Thanks..

 

I suggest you use opamps and active filters, far easier, cheaper, and more accurate than LC ones.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

dont forget about Doppler effect. If you go with bandpass, consider that sirens moving away from you (likely) will sound lower in frequency and sirens moving toward you (also likely) will sound higher in frequency.

Only at zero relative motion will be truly at frequency that sirens put out.
So, try not to make it too narrow band or else detection may be tough.

 

I was playing with idea to produce something like that. The main obstacle I bumped in is usage in car, since I couldn't get microphone sensitive enough to detect siren in the car.

 

I have a friend that has a interrior shop that will mount them outside.

If I can get a dicrete bandpass filter, I will be happy. Best I have founf is with OP AMP, may have to go that way for the gain, like you point out with the mic in the car.

 

One of the ideas was to detect windshield vibration.
I assumed loud siren would make it vibrate. But then other projects got in the way so I postponed experiments with it.

 

Did you get the filter working? I was looking at an op-amp circuit, RC bandpass with gain of 1000.. To start. Looknig to get away from the breadboard. I have circuit maker. Maybe I will try that. Will share what I find if you are still interested.

 

I didn't get that far, but I am still interested in the project. So please, if you manage to get further do share your results.

 

I would think that the best way to hear a US siren will be to use a small DSP chip. The reason is that you would need to have a filter that finds and then tracks the rising and falling frequency and then checks the rise and fall times against some timing limits to confirm that it is a siren sound. This tracking filter idea would be pretty tough to do in an all-hardware filter so why not use a DSP instead?

__________________
RadioRon

 

I have not done anything with DSP.. If I ever get a life it was in my top 10. I know the PICS have them now, so maybe I should look at that idea.

I'll go check them out. So mic to opamp to PicDSP. Maybe I can find a good PicDSP tutorial (after I check their price)