Traffic Lights with audio monitor

[gunits]

HI there,
I have a project to be done at school: I have to build a traffic lights to monitor de volume in discotheque etc... The traffic light should consists of a bright yellow official traffic signal with Red, Yellow and Green as standard. A microphone built into the unit monitors the sound in teh disco. For low levels of sound, the Green light is illuminated. As the sound level in the monitored area increases, the Green light will go out and the Yellow light will come on. For greater levels of sound above that which causes the Yellow light to light, the Yellow light will go off and the Red light will go on. Please bear in mind that the International standard of SOUND should be respected >65 dB. Please help me with the circuits and also a little explanation. THnx in Advance

 

[monkeytree]

i would suggest using LEDs for the lights but beyond that sound limits is tooooo!! confusing
Ca'va?

 

[Oznog]

Lots of ways to do it- as usual, a microcontroller may be your best bet for a low component count, well featured system.

The main difficulty here is in the design and calibration of the sound transducer. You don't want it to go off from people stomping the floor next to the device or just because one person is talking loudly nearby. A microphone will always pick up nearer sources of sound as stronger than the ambient sound level. As such you need either multiple sensors around the building or one located far from a particular sound source- like in the middle of the ceiling (unless there's a speaker there). You may also want to decide about how sensitive you want to be to peak noise- if it's just one brief thud from the sound system over the threshold, do you want that to put you in the red or only if the average level over the last 10 sec was too high?

 

[mettula]

using lm3915 may solve it up

 

[audioguru]

Yeah, the LM3915 would be perfect, except it isn't made anymore. One might sill be available somewhere.

 

[FRIED]

It is still in production
**broken link removed**

 

[audioguru]

Hi Fried,
Oh goody! I was mistaken. The logarithmic response of the LM3915 is very important for measuring sound and light levels.

I still have some National Semi modules with a LM3915 die hidden under a tiny black blob, and a LEDs strip all on a tiny pcb. They are pretty old, and LEDs in those days weren't very bright, so I might drill-out the tiny LEDs and replace them with modern ultra-bright ones.

 

[stevez]

Any chance you could use a PC with sound card? It seems that there is a lot of audio spectrum analyzer software available - you might employ that .

Usually the dba scale is used for hearing issues and sound pressure, not sound power is what you'll likely be measuring. Regarding hearing conservation - exposure limits are somewhat time related - though there are instantaneous limits. That certainly makes things more complicated.

Back to dba - you might want to understand how your microphone responds and attenuate or boost certain octave bands to come close to dba or normal hearing. If I were doing what you are doing I'd go get the graphic equalizer that my son purchased years ago and put it to work - use it to get the microphone to respond at least approximately like normal hearing. You might then follow with the log response devices already discussed. A pair of log response devices might be employed - one set for fast response and high level to address an extremely loud/short sound and the other dampened somewhat (capacitor maybe) and set at a moderate alarm level so it rides thru momentary peaks. Apply some simple logic so that one or the other can trigger the lights.