Minimalist sound detector

boriz

Senior Member
The Picaxe internal comparator can be configured as an op-amp. See this app note tip #12. Using a comparator this way is not ideal and will probably cause some harmonic distortion, but that's irrelevant with regards to a go/no-go sound detector. Neat huh?

I'm not set up to try this ATM, but probably will eventually. Any takers?
 

mrburnette

Senior Member
Neat, ugh? So, like the trick here would be to use one of the larger TDK, Murata, or similar piezo-sounders that can also be a decent voltage producer.... Then the same device could both produce sound & detect sound.... Like using a LED for detecting and producing light. Cool if the 'right' transducer can be specified.

- Ray
 

fernando_g

Senior Member
My take on this, is that unless one is extremely constrained in board area and/or cost, it is best to use an actual opamp if required.
 

boriz

Senior Member
Come to think of it, does it even need to be configured as an op-amp?

EG: If one input is DC stabilized to a reference voltage (provided internally by the DAC) and a Piezo is placed across the comparator inputs, then the comparator output should, because of the small input offset voltage, switch high or low and stay there until an AC signal from the Piezo causes it to start toggling at the 'sensed' audio frequency. The signal amplitude just needs to be larger than the (usually very small) input offset voltage.

How minimalist its that! No external components at all. Just a Piezo disk. Or maybe a moving coil mic.
 

MikeM100

Member
I would exercise caution using piezos connected directly to a PIC input ! Some years ago I used a weighted piezo sounder disc, as a 'vibration/movement) detector in a product. Reports of 'product not working' on delivery/installation were eventually diagnosed as a 'blown' PIC input on the piezo port !? Problem was when the product was dropped during shipping the piezo generated about 100V p-p and blew the input port (despite the PIC protection diodes). An extra series current limit resistor and external diodes fixed the problem

BTW is it not usual to have some form of envelope detector circuit for a sound detector ?
 

boriz

Senior Member
I'm just discussing the possibility of an ultra minimalist sound detector. First things first, would it work?

I'm not set up for any Picaxe prototyping ATM. I'm hoping someone will try it.
 

erco

Senior Member
Then the same device could both produce sound & detect sound.... Like using a LED for detecting and producing light.
Exactly how these little keychain finders worked, 15+ years ago. A single piezo disk senses whistling (remarkably sensitive) then beeps. Circuit also flashes an LED. Works well over a year on one or two button cells. They're a dollar on Ebay. I've used these as triggers for a few uC-controlled circuits. http://www.ebay.com/itm/LED-Light-Torch-Remote-Sound-Control-Lost-Key-Finder-Locator-Keychain-HS-/190853915822?pt=LH_DefaultDomain_2&hash=item2c6fc7a4ae#ht_2341wt_917
 
Top