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need more help with sound trigger

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gvi70000

Member
hello,
I need to trigger a camera using the sound made by the splash of a drop of water. The sound is picked up using a electret mic placed at about 20-30 cm from the sound source.
The best i could think of is posted here https://www.electro-tech-online.com/threads/canon-450d-remote-control.99225/ but with this design i have to place the mic too close at about 2 cm from the sound source
I also need to adjust the level at witch the camera is triggered (for popping balloons or water drops).
Can anyone help me to achieve this?

PS: I've uploaded two picture with the results I've got so far
 

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ke5frf

New Member
The only suggestion I would make would be non-electronic. At sporting events the camera crews use special parabolic microphones to pick up players and coaches from a good distance.

Of course working out some geometry would be involved, but you might try to mount the electret to face inward in the middle of a parabolic shaped bowl, with the focal point directed at your target and see if you get some mechanical amplification that way.

This might buy you several extra cms or even a meter or two...who knows.
 

Karkas

Member
This is a sound level indicator, I don't know if it will work, I've made that and at the lowest level it is sensitive, but I don't know if it will be for you, maybe the sound of a drop of water is not very loud for it to detect it, but you can vary the resistors to very low values or maybe you can add another Op. Amp, but that is only a guess 'cause I haven't studied them, i'm sorry it is in spanish, but they areonly a few words.

The LED will lit when the sound level is reached.
 

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gvi70000

Member
thanks for the reply
I'm thinking at a preamp with two or three transistors with adjustable gain
a few day ago i was googleing for the same thing and i found this circuit
Amplified Ear - RED - Page38
i made it up to P1(adjust volume) but it doesn't do the job
 

Karkas

Member
Hello gvi70000
Doesn't do the Job or doesn't do anything?
What if you make one of those circuits and amplify the output? wouldn't a simple solution like that work?
 

gvi70000

Member
the circuit in the link triggers the camera, but only from about 5cm from the sound source...so it doesn't do the job

"What if you make one of those circuits and amplify the output? wouldn't a simple solution like that work? "

amplify the output...you mean to put one more transistor at the end? I don't understand...can you me a little more specific?
 

Karkas

Member
Well what i ment was, if the problem is that the output gives a very low current instead of that the mic is not detecting anything farer than 5cm, then if you amplify the output you might be able to have a better sensibility, but maybe you'll have to measure the current in the output to know if there's a little one, or there is no current, but I don't think so, the mic of my cellphone is very sensitive, and I just made a test trying to record the sound of the drops of water and it didn't record it, Maybe some expert can give a very effective solution. Maybe you need a more sensitive microphone or a solution like ke5frf gave.
 
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gvi70000

Member
i will do more research and maybe some one with more experience will give me a solution.I you find a solution , please let me know.
Thank you for replying
I will let you now if i came up with something
 

Karkas

Member
Of course, post your results when you find the solution or I should say a solution.
Good luck.
 

Sceadwian

Banned
Why are you using audio in the first place? An infrared LED and detector will work very well. With the microphone you have to account for the time it takes the sound to travel to the transducer.
 

Mr RB

Well-Known Member
I agree. An optical sensor ABOVE the camera will give much better timing as it is independent of drop frequency, and gravity is constant so the drops fall at the same speed after triggering the sensor and will be at the same position in height when the flash goes off.
 

audioguru

Well-Known Member
Most Helpful Member
Are you using the Cmos LMV722 dual opamp?
The circuit will not work with many ordinary opamps.

The Cmos opamp has a gain of about 4000 which is more than enough. But the transistor that feeds it is saturated because the trimpot is not set correctly for it to be an amplifier. The trimpot needs to be set to about 1.4k which is impossible with a 500k trimpot. Try a 5k trimpot instead and adjust it near one end so that faint background sounds trigger the circuit.

Or remove the transistor that is not biased correctly.
You might as well remove the diode that does nothing in this circuit.
 

gvi70000

Member
yes, I'm using lmv722m as a comparator
unfortunately i disassemble that mic circuit
now I'm using this one but it actually is worst that the one before

PS: The 1n4148 i forgot to delete it from the simulation circuit, i didn't use it in the circuit
i was too when i test the circuit for the first time
 

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gvi70000

Member
do you think it is ok to remove the transistor?
Because i forgot to mention that between the op amp and the transistor circuit i use a stereo cable about 1m long
 

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audioguru

Well-Known Member
Most Helpful Member
If the 100k trimpot is set to about 105k (plus and minus depending on the gain of the transistor) then the circuit will be very sensitive. But since the transistor does not have any DC negative feedback then it is also sensitive to temperature changes.
The transistor will also amplify changes in the supply voltage.

I was taught that such a simple transistor circuit should never be used for anything.
 

gvi70000

Member
Thanks again for replaying Audioguru,

I've change the pot with one of 10k + ore 10k resistor in parallel(i don't have a 5k right now) and the result was almost the same in sensitivity..so i change the 2n2222 with a bc547 (measured gain is 650) and the sensitivity has increase a little bit. Maybe the mic is not sensitive enough - i think is a Velleman with a sensitivity around -68dB and a nominal voltage of 4.5V - next week i will receive a new mic BCM-9767P from BE-STAR -44±2dB (VS=3V/RL=2,2kΩ) i hope that will do the job.

Do you think is a good idea to remove the transistor near the mic as i connect the mic preamp with lmv722 input with a stereo shielded cable about 1m long?
 

audioguru

Well-Known Member
Most Helpful Member
You need to learn about transistors to see that yours were designed completely wrong.

If you bias the opamp properly and use negative feedback then it should work fine without a transistor. But that opamp has a much lower max gain than normal opamps.

I don't know if the very short sound duration is enough to trigger your camera.
 
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