EEVblog #964 - Mailbag

Mailbag is back for 2017

SPOILERS:
Educational kits from

Electro-permanent magnet for UAV's and drones from NicaDrone

Cisco VOIP phone teardown

1980's GE Cordeless phone teardown

Open source USB charger:

STM32 Development board:

Max Chan is for hire:

Support the EEVblog through Patreon!

EEVblog Amazon Store (Dave gets a cut):

[photonBG]

The Cisco IP phone does NOT use a standard power over ethernet pinout, they use their own pinout. Because clearly standard power over ethernet does not provide the optimal configuration for the best VoiP experience, but changing the pins around makes it perfect.

[mikeselectricstuff]

The copper lands can also be to balance the amount of copper on each side to help with the plating process - Eurocircuits online DRC checker will sometimes complain about designs with a big difference in density between sides.

[LasseHuhtala]

"I won't take it apart.. or maybe I will." - Dave 2017

[mikeselectricstuff]

Those caps have series resistors (typically 100R), not inductors - they're snubbers for use across contacts - the resistor limits surge current when the contact closes

[craiggordon]

Hi Dave:
I took the plung and decided to try Tron Club. Ill keep you updated as the kits come in. thanks for the channel

[dextrodemon]

i think when there was that bit of residue magnetism with the electro-permanent magnet thing it was because you had magnetized the steel plate you were demonstrating it with.

[denniswoycheshen]

glad you are back... was having withdrawal.

I think I might join the tron club. this would be perfect to show my daughters how circuits work. and also help me understand how electronics work. thank you for posting this. I've been watching your videos for a long time and never miss a mail bag. thank you Dave.

[steverobbins]

Did you notice the crappy layout on the Cisco IP phone? There are some DC/DC converters on the board, and they put the high-current loops on inner layers, rather than on the surface. That means their switching current run through the ground planes, probably making the whole board pretty noisy. Basic rule for beginner power supply designers: keep the two current loops tight and on the surface, and connect to the inner power/ground planes with vias only at the input, output, and common nodes. I haven't seen any videos on YouTube about this, so it might be a good subject for one of yours, Dave.

[electronicsNmore]

I remember that GE cordless phone. They were very easy to eavesdrop using a scanner. You also hear other people's conversations on the same frequency. LOL 49.975 mhz.

[nekomasteryoutube]

Always nice to see another Mailbag, first one of the year too ;)

I hope you and your family enjoyed your vacation/get away Dave.

- A random Canadian

[omitsura]

Cisco is convoluted way of doing anything! I recall someone commenting semi-jokingly that back in the days, their security was provided by the fact that there were so many different builds made for router os.

[gingatim]

A bit of info on the Cisco phone...

We are still using these exact phones for all desk communications. I work for a government department where calls made NEED to be secure. These are part of few fully closed systems left on the market. By fully closed, I mean we run the whole system, from call managers to end phones. The only thing that anyone else controls are the phone number allocations (we have a block of numbers we can allocate). The main feature of the phones we care about is the encryption. If someone makes an internal call from one phone to another, the call is encrypted end to end. Not even myself as an IT administrator can listen in, even though I have full control of the system.

[LeoHL]

Dave, the PWM input is what is used for controlling it, you would connect that to a spare R/C channel, R/C model systems use PWM for all servo and speed controller control inputs, typically it is a pulse that varies between about 1 and 2 milliseconds.

[gregadams]

The interface is a one-port PoE switch. You connect to a PoE switch and then connect your pc/laptop to the port for IP traffic. The other port is for console headsets and such. We still use them in the US.

[mballew]

its certainly not long term reliability on the Cisco VOIP phone. We use those at work and we've had to replace several units because the hook switches would fail after just a few months. Especially in areas where the humidity would be a bit high. So many issues from those phones

[bulwinkle]

That's one way of disposing disposable wrist straps! 😂😂😂

[JennyEverywhere]

Those pushbutton-pulse dial phones were weird, but I took a lesson from them and built a relay-driven pulse dialer that connected to the joystick port of our Apple II+. With a database I built in Applesoft, I would use that to dial into bulletin-board systems nearby, so we could connect via acoustic coupler modem.

I believe the neon bulb in the antenna line was a low-tech static protection. It gave some bleed off in case there was a nearby lightning strike, or shocky carpets.

Brings back memories...good times, good times...

[canadianavenger]

The TronClub stuff is interesting. Looks like maybe the 2nd kit you got is actually the 1st kit, but from the Advanced stream, as both are "Kit #1" in the menu. [would explain the double bread-board]

[krypticmac]

good evening Dave!!! So happy your back hope holiday was great for you. Been looking forward to you coming back.

[airthrow]

I really like the tronclub and the permanent magnet module! These might be the first items I get that I learned about on eevblog...advertisers take note!