Light/ Dark, sound sensor problems

Hello,
I need some help to create two sensors using LMV 721/722 OpAmp
One will be a light/dark activated switch for one led and the other a sound activated switch. Both must have sensitivity adjustment.
The light circuit I've manage to get it work only for the switch part (switching the In+ and In- of the op amp), the sensitivity one..no luck, as for the sound sensor nothing till now (the microphone is a capacitor one).
The supply will be a 3V Li battery.

Can any one please help me to solve these circuits?

PS: I'm new in this field... so have some understanding

Thank you.

As you were told on the other website, your sound sensor opamp circuit is completely wrong.
Its max gain is only 3. It should be somewhere from 30 (screaming into the mic) to 300 (talking softly into the mic).
The mic is an electret type, not a capacitor (condensor) type.

C2 charges into the base-emitter diode of Q1 on the first positive-going sound then has nothing to discharge it so that Q1 can be turned on again on the next positive-going sound. Then the LED briefly blinks one time if there is continuous sound.

What do you thing about this one?

gvi70000 said:

What do you thing about this one?

Click to expand...

The LED is lighted all the time on your new mic preamp circuit. Guess why?

wrong side of the transistor


I want to build a camera shutter trigger with a light and sound sensor.

When the microphone detects a sound the shutter is on. I need to adjust the sensitivity to not have false triggers. To see the threshold that triggers my camera i need the led (actually there will be one more transistor -same base as first one - that closes the camera trigger circuit)

For the light sensor i need two modes:
1. Trigger at lighting or other flashes (sudden light increase)
2. To trigger when a beam of light that falls on the photo diode is interrupted (to get nice pictures of water drops).

This is what i want to achieve.

Instead of photo diode i an use a photo transistor, but it has slower response and I've read that for this type of application BPW will do a better job.

Hello,
I think I've made some progress here and i need your opinion
What I'm not able to do is to change the circuits sensitivity so i need some advices.
One more thing, do you think it is possible to increase the time of led (D1,D2) being lit without using a 555? If yes, how can i do it?

Thank you

I think i get the sensitivity part working (not sure at all) on the light sensor but for the sound I've got nothing.

Please, it must be somebody out there who is willing to help me solve these problems

PS: I found somthing similar but it uses a micro-controller, maybe it will give you an idea https://www.doc-diy.net/photo/smatrig/