EEVblog #827 - Mailbag

[mrkva]

Hey guys, creator of Elektrosluch here. Hit me up if you have any ideas how the device can be improved. It will always remain open source for future generations! )
I am now comparing different opamps, and getting quite different "range" with LME49720. It is slightly lower noise, but also it also catches different signals then OPA2134. To be more exact, it catches frequencies which don't even appear with OPA2134 (I would expect them to be there but maybe lower - as an effecto of LP filtering). Don't really know why. Wonder if anyone has a explanation.

[open loop]

The Electroslutch reminds me of what happened when I turned on my ZX Spectrum while the AM radio was on. Didn't the legendary Bill Herd say something about how a computer did not "sound" right during an amp hour because of its interference on an AM radio.

Great work on it though would be interested in playing with the circuit myself when I get time.

[rollatorwieltje]

Why would you use that Remoteboot thing when you can do the same with Wake on Lan? Many routers have it in their web interface. To my surprise I can even wake up my Macbook via wifi (from sleep mode, didn't try complete power off).

[mikeselectricstuff]

Hey guys, creator of Elektrosluch here. Hit me up if you have any ideas how the device can be improved. It will always remain open source for future generations! )

Built-in speaker would be the obvious one

[SeanB]

Why would you use that Remoteboot thing when you can do the same with Wake on Lan? Many routers have it in their web interface. To my surprise I can even wake up my Macbook via wifi (from sleep mode, didn't try complete power off).

WOL depends on sending a "magic packet" which is not transmittable out of the LAN. It is an Ethernet packet with the MAC of the card, and not TCP/IP, so will not traverse a router. Enabling a router to respond to WAN commands is not considered a good idea, there you really do want a very good security protocol, otherwise scans will find it and things happen afterwards.

Sleep as well ( depending on the actual level) just means the screen is off, and the system is running at the lowest speed the processor can run at, along with all RAM swapped out and most applications not given any processing time, the processor only responding to interrupts and the hard drive being commanded to idle. Low power state, not off.

I hope the OP is implementing very good security on the device, as it will either be open to packets via a DMZ on a router, or will be internet visible. Checking the sending side is within an acceptable network block ( reduce the sites that can attack to the IP block of the main user) along with using a good long password or PKI communications are really needed. There are enough vulnerable IOT devices out there already.

[EEVblog]

Hey guys, creator of Elektrosluch here. Hit me up if you have any ideas how the device can be improved. It will always remain open source for future generations! )

Built-in speaker would be the obvious one

+1

[bitwelder]

Designer of Remoteboot here, the ground plane now has a cutout under the antenna, thank you all for the feedback.

How about making a version of the RemoteBoot with a different variant of the ESP8266 (perhaps the ESP-07) that has the antenna connector, so to bring the antenna outside the PC case?

[rollatorwieltje]

Why would you use that Remoteboot thing when you can do the same with Wake on Lan? Many routers have it in their web interface. To my surprise I can even wake up my Macbook via wifi (from sleep mode, didn't try complete power off).

WOL depends on sending a "magic packet" which is not transmittable out of the LAN. It is an Ethernet packet with the MAC of the card, and not TCP/IP, so will not traverse a router. Enabling a router to respond to WAN commands is not considered a good idea, there you really do want a very good security protocol, otherwise scans will find it and things happen afterwards.

Sleep as well ( depending on the actual level) just means the screen is off, and the system is running at the lowest speed the processor can run at, along with all RAM swapped out and most applications not given any processing time, the processor only responding to interrupts and the hard drive being commanded to idle. Low power state, not off.

I hope the OP is implementing very good security on the device, as it will either be open to packets via a DMZ on a router, or will be internet visible. Checking the sending side is within an acceptable network block ( reduce the sites that can attack to the IP block of the main user) along with using a good long password or PKI communications are really needed. There are enough vulnerable IOT devices out there already.

Dave said he uses a VPN, so I assume he can already securely access his lab network from home. That's how I used it. My router was also a VPN endpoint, so I could open a VPN to it from anywhere, log in on the web interface and send the WoL packet. I used it to wake up a powered off (really off, as in shut down) desktop pc via ethernet.

I was just surprised I could also wake my laptop, I thought WoL wasn't supported over wifi.

[mrkva]

Hey guys, creator of Elektrosluch here. Hit me up if you have any ideas how the device can be improved. It will always remain open source for future generations! )

Built-in speaker would be the obvious one

+1

Thanks for the suggestion Dave and Mike! Any suggestions for low-part-count & high fidelity solutions for amp+speaker? I experimented with LM386, but I'd like to go more hi-fi with this one (more like "laptop speaker quality" - i don't expect wonders). Probably some monolithic Class D solution would be optimal for the amp, since battery life is important to me.

[jancumps]

The on-board audio can be simple, just a tactical tiny mini speaker. You can always keep the audio-out plug that's already there for the audiophile user 

[Fungus]

The on-board audio can be simple, just a tactical tiny mini speaker. You can always keep the audio-out plug that's already there for the audiophile user 

I imagine the stereo sound is useful to more than audiophiles...

[Brumby]

... like an EEVblogger.

[sakujo7]

Just look for any ferrite inductors with open magnetic systems, and anything from around 1mH upwards will work, current capacity not too important.

Can confirm that lower inductors work.

I "built" a "poor man's" version by attaching a 470uH wire-wound inductor to a uCurrent (nA range, effectively a x100 amplifier with 10k input impedance). Output directly connected to headphones, though a series pot is a good idea if you value your hearing.

[mrkva]

From my experience higher values have more sensitivity & different frequency responses. 22mH/33mH seems to be optimal in combo with OPA2134 opamp, but I am also working on bigger hand-made antennas.
BTW if anyone builds one, I'd love to see some pics!

[Seekonk]

That ultrasonic transducer amplifier circuit that was mailed in with questions reminded me of a question on another forum.  At least I hope that is this mailbag.  That circuit has an interesting property.  This other poster wasn't getting the gain that he expected from the resistor combination of the first inverting amplifier.  It wasn't the op amp and everything was working as it should.  I love simple circuits like this that have a built in feature.  Can you guess what it is?

[ondrejko0102]

Hi, I am from Slovakia too. Elektrosluch are two words - "Elektro" and "sluch" meaning "Electrical" "hearing" :-)
PS: Happy New Year!?

[harnon]

Just randomly watched this mailbag, @36:22 Dave comes within about 1mm of slicing his finger in half using the Crocodile Dundee knife