I need a sensitive audio trigger for a 555.

[bigkim100]

I need a sensitive audio trigger for a 555.
I would like to use a small microphone element that triggers a 555 when the audio element is brushed or bumped.
I guess it would be best if there was adjustable sensitivity for the trigger Microphone.
I would like the 555 to be timing on for around 5-10 seconds (adjustable).
I dont care about the voltage, I can apply anything, but it does need to be battery powered.
Thanks in advance for any help

 

[AnalogKid]

I think the mic signal level will be so so close to a comparator's input offset voltage error that you'll need a preamp stage for each mic.

4 mic elements
4 preamp circuits (one LM324)
4 comparators (one LM339) wire-ORed to a single 555 Trigger input

However - the mic elements will not be able to differentiate between being brushed (a quiet noise close-up) and a yell, hand-clap, or other loud noise far away. How will you account for this?

ak

 

[bigkim100]

I think the mic signal level will be so so close to a comparator's input offset voltage error that you'll need a preamp stage for each mic.

4 mic elements
4 preamp circuits (one LM324)
4 comparators (one LM339) wire-ORed to a single 555 Trigger input

However - the mic elements will not be able to differentiate between being brushed (a quiet noise close-up) and a yell, hand-clap, or other loud noise far away. How will you account for this?

ak

Im sorry, analogue, I have changed the specs to be only 1 channel. 1 mic, 1 amp 1 555 for timing.

Quote:"However - the mic elements will not be able to differentiate between being brushed (a quiet noise close-up) and a yell, hand-clap, or other loud noise far away. How will you account for this?"
I am hoping that there can be a sensitivity adjustment, so that a simple brush against the microphone will start the 555 timing

 

[bigkim100]

https://www.internationaljournalssr...ssuepdf/ICETST/2018/ECE/IJECE-ICETST-P101.pdf

I came accross this schematic.
If it is too sensitive will removing one of the 2 transistors make this less sensitive??

 

[AnalogKid]

Yes, but there must be other changes. Each of the transistor stages inverts the logic polarity of the signal. As it is shown, the bias current through the mic element keeps the first transistor on all the time when things are quiet. An audio negative peak that is large enough will turn off the first transistor, which turns on the second transistor, which applies low signal to the Trigger input through the capacitor. If one transistor is removed, then the mic and its bias resistor must be transposed.

You can add a sensitivity adjustment to this circuit by adding a pot in series with the 4.7 K resistor.

Also, the circuit has a critical error. There needs to be a resistor from the trigger input to Vcc to keep the input biased off between pulses.

Note - I know this is not your drawing, but it is an excellent example of why reference designators are *crucial* in discussing circuit.

ak

 

[bigkim100]

LOL...thank you ANALOGUE...thats why I always run it through this forum

 

[Audioguru]

The microphone is not a condensor type, instead it must be an electret type. A translation problem from the distant country.

The microphone's shield is its wrong output that will pickup lots of interference. The positive wire of an electret mic is its shielded output. The school kid in Hyderabad does not know that.

The 1k collector resistor of the first transistor needs a massive current that will quickly kill the battery and the tiny current in the electret mic might not be enough to properly turn on the transistor.

Your problem is that any sound will trigger the 555. The two transistor preamp does not have a tuned circuit to respond to only one frequency, it also does not have a timer to respond to only a beep with a certain duration and it does not have a counter to respond only to a certain number of beeps.

 

[AnalogKid]

any sound will trigger the 555.

Any sound that is loud enough to turn off the first transistor.

ak

 

[Audioguru]

Any sound such as a dog barking, a motorcycle, airplane or noisy car, the TV or radio, a door bell, telephone ringing, people talking etc.
The circuit that was copied was to detect loud hand claps, not just the faint brushes on the microphone.

 

[Bluejets]

Maybe use a touch switch instead.
Can be made with a couple of small transistors in darlington setup.