Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

need more help with sound trigger

Not open for further replies.


Member level 5
Sep 29, 2009
Reaction score
Trophy points
Activity points
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 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

Why do you have to adjust the level? If a water drop triggers it, then a balloon popping will trigger it, too. You're just checking for an event, not recording the sound.

I need to adjust the level to not have false triggers.
Anyway, my problem is that i have to place the mic too close to the sound source and i need the mic placed at 20-30cm away from where the water drops are falling.

Honestly, I don't understand this circuit. I don't know if that's because the circuit's wrong or because it's just unfamiliar to me, but if that's just a normal op-amp, it looks like you have no negative feedback at all, so the op-amp's just running at full tilt and acting like a comparator.

Can you look at the output of U1 with a scope?

Try adding a pot between pins 2 and 6 of U1 to vary the gain and a resistor between the transistor and pin 2, so the op-amp is running as an inverting amplifier.

Added after 9 minutes:

In fact, the image on that **broken link removed** is a inverting amplifier used to amplify an electret, which is exactly what you're doing. Why not just copy that?

**broken link removed**

Like I said on the other website, the transistor is saturated and is not amplifying because the value of the 500k trimpot as its collector resistor is much too high.

Use a 5k trimpot and adjust it to about 1.4k then the circuit will trigger on faint background noise.

Then there will probably be a problem that the water drip sound will be to short in duration to trigger the camera.

It's only 500k at the end. If it's an audio taper 500k pot it will still have a usable range.

Thanks for replaying Audioguru and Endolith,

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 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 that if i make a Darlington pair with 2 BC547 will increase the circuit sensitivity?

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?

You need a preamp with voltage gain and that is biased properly. Your transistors weren't.

Don't use a darlington because its voltage gain is the same as for an ordinary transistor but it has a very high current gain that you do not need.

I already replied to your other thread on the other website so I won't repeat it here.

Not open for further replies.

Part and Inventory Search

Welcome to