astronomerroyal
New Member
Hi,
I'd like your valuable opinions regarding this acoustic trigger that I'm designing.
Function: To generate a pulse when a sufficiently loud sound is sensed. Acoustic sensitivity and pulse duration are adjustable. This will be used with some other equipment to fire a camera, to take, for example, a photo of a balloon popping.
I've attached a schematic of the circuit, which works quite nicely on my breadboard. I aim to make a PCB (my first).
How it works: schematic reads left to right. Electret mic senses sound (circuit from https://www.epanorama.net/circuits/microphone_powering.html) which is amplified by 386 audio amp (Gain=200 using extra capacitor, datasheet circuit). This signal out is centered about +V/2 and is fed into comparator which compares it to user-adjusted voltage ('The Sensitivity'). I believe the comparator effectively produces a 'one bit' digitization of the audio.
The pulse is generated by a 555-timer monostable circuit (standard Mims circuit). The leading edge of a sufficiently loud sound opens the comparator gate, sending the 555 trigger low and a pulse is started. The switching transistor on the right merely flips high-to-low for feeding into my camera equipment.
I'm new to using Eagle (Lite), so...
I'd like to get your advice on its design, whether the schematic is drawn properly and the different sections connected sensibly. I tried putting decoupling caps* here and there on the breadboard, and the results were unpredictable, sometimes it helped with reducing noise levels, sometimes not. Any rules for this? I examined the noise levels with a scope and also using iPod headphones (w/ capacitor in series to block DC) tapping into amplifier output.
I don't really know how to connect the comparator to the 555. I'm using a resistor (R2) in between them, because I recall that the 555 was being retriggered before it had finished its pulse. Not sure why and I don't claim the resistor makes sense - just seems to help a little.
* not sure my terminology is right. I refer to ceramic caps place across power pins etc.
My first few attempts at arranging it into a PCB design have been disastrous. Do you have any tailored advice for routing this circuit? Is it a two layer job? I'm using 'Hobbyist Eagle design rules' by instructables.com user
[URL="https://www.instructables.com/id/Make-hobbyist-PCBs-with-professional-CAD-tools-by-/?ALLSTEPS#step12"westfw[/URL]
. Fat traces etc. There certainly seems to be enough room on the Eagle Lite board for all of this.
I'll leave it there for now.
As always, my thanks in advance,
AR.
I'd like your valuable opinions regarding this acoustic trigger that I'm designing.
Function: To generate a pulse when a sufficiently loud sound is sensed. Acoustic sensitivity and pulse duration are adjustable. This will be used with some other equipment to fire a camera, to take, for example, a photo of a balloon popping.
I've attached a schematic of the circuit, which works quite nicely on my breadboard. I aim to make a PCB (my first).
How it works: schematic reads left to right. Electret mic senses sound (circuit from https://www.epanorama.net/circuits/microphone_powering.html) which is amplified by 386 audio amp (Gain=200 using extra capacitor, datasheet circuit). This signal out is centered about +V/2 and is fed into comparator which compares it to user-adjusted voltage ('The Sensitivity'). I believe the comparator effectively produces a 'one bit' digitization of the audio.
The pulse is generated by a 555-timer monostable circuit (standard Mims circuit). The leading edge of a sufficiently loud sound opens the comparator gate, sending the 555 trigger low and a pulse is started. The switching transistor on the right merely flips high-to-low for feeding into my camera equipment.
I'm new to using Eagle (Lite), so...
I'd like to get your advice on its design, whether the schematic is drawn properly and the different sections connected sensibly. I tried putting decoupling caps* here and there on the breadboard, and the results were unpredictable, sometimes it helped with reducing noise levels, sometimes not. Any rules for this? I examined the noise levels with a scope and also using iPod headphones (w/ capacitor in series to block DC) tapping into amplifier output.
I don't really know how to connect the comparator to the 555. I'm using a resistor (R2) in between them, because I recall that the 555 was being retriggered before it had finished its pulse. Not sure why and I don't claim the resistor makes sense - just seems to help a little.
* not sure my terminology is right. I refer to ceramic caps place across power pins etc.
My first few attempts at arranging it into a PCB design have been disastrous. Do you have any tailored advice for routing this circuit? Is it a two layer job? I'm using 'Hobbyist Eagle design rules' by instructables.com user
[URL="https://www.instructables.com/id/Make-hobbyist-PCBs-with-professional-CAD-tools-by-/?ALLSTEPS#step12"westfw[/URL]
. Fat traces etc. There certainly seems to be enough room on the Eagle Lite board for all of this.
I'll leave it there for now.
As always, my thanks in advance,
AR.
