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Amazon Echo Flex: Microphone mute button appears to be real and functional

electronupdate.blogspot.com

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Re: Amazon Echo Flex: Microphone mute button appears to be real and functional

#41

Post by systemvoltage »

Uhhrrr wrote: post #33
systemvoltage wrote: post #29

Earlier quoted context omitted.

In order to use a physical debounce switch, there are several steep challenges. You can imagine OP presenting to an audience of 14 people at Amazon Devices group with a slide titled "New BOM proposal" entailing 6 million devices x [$0.0273 (switch price at 100k qty) + $0.05 assembly cost] + $50k engineering NRE (650 engineering hours) + $35k tooling NRE + $22k FCC re-cert + 7k ESD cert + another $100k in various cert…

OP should also Insist On The Highest Standards and remind them that OP is Right, A Lot.

Then OP sees newsflash on TechCrunch "Amazon Echo Flex v2 is failing in low humidity conditions". Goddamn it, Andrew (at the reliability lab). OP goes home and opens a bottle of Amazon basics wine.

Re: Amazon Echo Flex: Microphone mute button appears to be real and functional

#42

Post by bayindirh »

tangoalpha wrote: post #37

An OTA firmware update can change this behavior overnight. Unless it's a physical bounce switch that actually disconnects power mechanically, you are still at the mercy of someone else.

As far as I understood from the schematic [0], the power line of the mic is directly connected to the LED.

Looks like when you press the mute button, you both light the led up and pull-up the transistor gate (It looks like PNP so, it turns off when you apply power to the gate). This effectively cuts off power from the mic itself.

So, the LED is not controlled by firmware but, by the behavior of the circuit.

AFAIK, OTA updates cannot re-wire PCBs or do we have nanobots now?

[0]: https://1.bp.blogspot.com/-vVhoXpEtTXo/X_0iLmz9gcI/AAAAAAAAB...

Re: Amazon Echo Flex: Microphone mute button appears to be real and functional

#43

Post by gary_0 »

e9 wrote: post #21
chaboud wrote: post #15

Disclosure: I'm an Amazon Devices PE, but not on Alexa devices. Jeff (and others) have spoken publicly about this in the past, and this teardown is correct. The hardware is designed such that, if the privacy LED is on, the microphone is unpowered. In order to compromise that, one would need to physically alter/damage the hardware.

Why not physical debounce switch? I get it is more expensive but no one would question it twice.

There'd be no point: a suspicious end user would still need to test/dismantle the doodad connected to the power lines to see that it behaves as expected and doesn't contain anything nefarious. So might as well use a relatively standard electronics design.

Re: Amazon Echo Flex: Microphone mute button appears to be real and functional

#44

Post by bibabaloo »

tangoalpha wrote: post #37

An OTA firmware update can change this behavior overnight. Unless it's a physical bounce switch that actually disconnects power mechanically, you are still at the mercy of someone else.

Perhaps you could disable the button, but I don't think a firmware update can change the red LED on == microphone off behaviour. This is a good compromise IMO, as if the microphone off button stops working then you can deduce that the firmware may have been tampered with.

Re: Amazon Echo Flex: Microphone mute button appears to be real and functional

#45

Post by detaro »

tangoalpha wrote: post #37

An OTA firmware update can change this behavior overnight. Unless it's a physical bounce switch that actually disconnects power mechanically, you are still at the mercy of someone else.

How does a firmware update change the hardware on the board?

Re: Amazon Echo Flex: Microphone mute button appears to be real and functional

#46

Post by bigiain »

tangoalpha wrote: post #37

An OTA firmware update can change this behavior overnight. Unless it's a physical bounce switch that actually disconnects power mechanically, you are still at the mercy of someone else.

As I understand the teardown article, it is impossible for a firmware update or any malicious SOC code to enable the microphone without also turning the red led off.

Not as good as a physical switch I guess, but better than some implementations of laptop webcam activity lights at least...

Re: Amazon Echo Flex: Microphone mute button appears to be real and functional

#47

Post by bigiain »

renewiltord wrote: post #38
coldtea wrote: post #17

Earlier quoted context omitted.

The writers don't write for our amusement here and according to our criteria on HN, they writes as it pleases them. They went to the length to do a useful breakdown of a circuit, and write about it. They don't owe us some nice title, or some convenient summary so we don't read their post...

Haha, they don't, but we owe ourselves that so we should submit with that info.

That's not what the site guidelines say...

"Otherwise please use the original title, unless it is misleading or linkbait; don't editorialize."

Use the original titles.

Re: Amazon Echo Flex: Microphone mute button appears to be real and functional

#48

Post by bigiain »

mlyle wrote: post #13
pengaru wrote: post #11

So the microphone signal line isn't broken by the mute, got it.

No-- even better, the MEMS microphone is depowered.

Not sure that really qualifies as "even better"...

"Even better, there is no microphone", is about the only "even better" scenario than the signal lines being broken. A powered down active component is only "almost as good" at best.

Re: Amazon Echo Flex: Microphone mute button appears to be real and functional

#49

Post by mlyle »

bigiain wrote: post #48
mlyle wrote: post #13

Earlier quoted context omitted.

No-- even better, the MEMS microphone is depowered.

Not sure that really qualifies as "even better"... "Even better, there is no microphone", is about the only "even better" scenario than the signal lines being broken. A powered down active component is only "almost as good" at best.

OK, so you'd rather have a big, high gain, low output impedance amplifier enabled and driven with the audio waveform but the signal line gated... than the device unpowered and the signal line connected to ground via the ESD protection path in the package. K.

I'd have a decent chance at recovering the audio in the former case, but nil in the latter..

For instance, if it's gated with a FET, and then hooked up to a SOC ADC pin that's multiplexed with other functions, one could use those other functions to provide biasing opening the FET.

If it's gated with something better-- e.g. an actual relay-- the audio waveform may still be recoverable: it's very, very large in magnitude compared to how it is with the device unpowered, and will be consuming variable amounts of power with the audio waveform. You might be able to recover the signal by measuring power nets AC coupled with lots of gain.

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