microphones with very low current consumption

Piezoelectric (crystal) microphone.

Cheers

--
Syd

...I already have been looking for such components but still haven't found anything. Don't forget another requirement-low cost

That may actually work.

Or a bare electret element, to which you attach your own JFET, carefully controlled for current (although I must admit to having absolutely no clue of how easy it is to get bare electrets)

In any microphone circuit you should consider the amount of current you'll need in the following amplifier -- you certainly aren't going to get a transducer that can directly power the following equipment.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

Depends what you need. A simple piezo sounder element may suffice and is low cost. What sort of sensitivity and signal type? Just a whistle or a hand-clap or a Hi-Fi recording?

Cheers

--
Syd

A piezo buzzer, a small speaker or a headphone capsule.

How much is your high appreciation?

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

Correct me if I am wrong, but my understanding is that peizo mics generally have extremely poor frequency response. I'm hedging because that could just have been implementation, but I somehow doubt it.

-- Les Cargill

Yes they're not Hi-Fi, but the OP didn't specify, and they're sensitive. For some reason, crystal microphones retain a niche for use with mouth organs, which maybe implies a fairly restricted frequency response, but 'extremely poor' seems a bit extreme.

Cheers

--
Syd

And you're really sure the reason microphone manufacturers put those JFETs in there doesn't apply to you? Are you 100% fire-proof certain that you can live with the impedance you would have without that conversion?

Anyway, specifying a current consumption all by itself is somewhat devoid of meaning. Say there was a microphone with 1 µA current from a

100 kV supply. Would that satisfy your request? Or was it actually a _power_ restriction you were after?

Picky picky.

And, to reiterate, would an $0.10 microphone that needs no current and puts out a microvolt when you shout at it be sufficient, or do you have some sensitivity requirements?

(Because ceramic capacitors do tend to be microphonic. And cheap).

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

That depends on the following equipment. Sound-powered telephones are able to convert speech to electricity and back to sound with no amplification. Earmuff-type headphones and a loud voice made up for the losses in the signal path..(I suppose the dynamic range of the human ear certainly helps ! ;-)

A good voice-coil microphone would work with a lot of A/D converters. A peizo microphone might work with a transformer to match to a relatively high-impedance ADC input.

Mark Borgerson

Carbon microphones are electro-mechanical amplifiers; they put out more electrical energy than the mechanical energy needed to drive them, at the cost of needing way more bias current, at way more voltage, than an electret.

Early telephone amplifiers actually used a sounder connected to a carbon mic, and exhibited electrical gain.

True, but the OP has already ruled that out as he wants cheap. Dunno if he's already checked for pricing straight from China, though.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com

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Thank you all for your comments. I can't tell you yet the desired sensitivity requirements, but I would say I need quite sensitive microphone. After microphone I have MCU with 12-bit ADC and/or comparator, so it is better to get oversensitivity than undersensitivity. The device is to be operated by 3V Lithium battery, i.e. VCC range within

2.5-3.3V or, if I use volatge regulator, 2.5V. Regarding the idea to use capacitor as a microphone, actually electret microphone is a capacitor with JFET. There is an option to ask supplier for a part without JFET, and then, seemingly, I get a possible silution, however I get here a hard task here to amplify high frequency signals of microhone output with high impedance. All that with cheap and low current means.

Regards, Eli

That's doesn't feel right. Why try so hard to get the microphone's consumption all that far down, when your MCU is going to consume orders of magnitude more than that, anyway?

Good point. In order for the onboard ADC to digitize at audio rates, the MPU clock can't be slowed down too far, so the MPU power should be much larger than the drain through a FET on a microphone.

A good processing algorithm that minimizes the required CPU cycles might save a lot more power than you could ever save at the microphone.

Mark Borgerson

d s ,

Dear Mark and Hans,

In my application, signal processing is an asynchronic and a very rare task, so MCU will not wast its power for constant digitalization and signal processing, as you have assumed. Generally, MCU will be sleeping with slow wakeup period of 1 sec and will be woken up when some asynchronic event(for example one of microphone) happens. I would like to connect the microphone output to a comparator that will trigger MCU when microphone output goes over some threshold. All my application, without radio module, should consume

7-12 uA @ 3V in average. Eli.

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Dear Eli, I hope you already found the microphone, but I know is not easy. I'm also looking for a very low power electret mic, without success. Why you don't turn on the mic only for few miliseconds to check if there is the "event"? I suggest you take a look to the TI application SLAA389 for a glassbreak detector: A Robust Glass-Breakage Detector Using the MSP430. They turn on the mic for 20uS every 2.5mS. When the mic is on and the MCU is working (20uS) the current is 4.8mA, then for 2.5mS the MCU goes to low power and the current is 0.6uA.

Regards, Aldo.

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