49 votes
Accepted

Add a passive hardware token using a 3.5mm jack

Use 1-wire bus and any 1-wire chip inside the button. I wrote "any", because each 1-wire chip has its own, unique hardware address, so all that you need on RPi side is checking that the chip was ...
VillageTech's user avatar
  • 1,588
23 votes

Mains Plug Soldering Wires

Solder cold flows so it can work loose and cause problems with overheating, charring etc. It's worse than leaving the wires as-is. If you don't have ferrules, leaving them as-is would be a better ...
Spehro Pefhany's user avatar
19 votes
Accepted

Mains Plug Soldering Wires

Basically, this is in agreement with everybody else. What you had were either uninsulated ferrules which are tubular, or a small piece of brass etc. crimped on to do the same job. These are basically ...
Mark Morgan Lloyd's user avatar
17 votes

Why do EU electrical sockets/plugs have two pins for grounding?

Figure 1. Schuko sockets. (Image source: Bran.) If you are referring to these sockets the dual earth pins give balance pressure on the plug which would otherwise be forced to upwards or downwards ...
Transistor's user avatar
  • 176k
17 votes

Mains Plug Soldering Wires

Solder makes the copper strands brittle and the flux may oxidize it. It is not recommended to solder the wire ends. It likely ends up in loose connection under the screw which is a problem. This ...
Justme's user avatar
  • 149k
16 votes
Accepted

What type of plug is this?

That looks like a C11 plug. Might be hard to find from a legitimate source since it was withdrawn from the IEC 60320 standard.
vir's user avatar
  • 18.5k
12 votes
Accepted

Is it safe to swap positive and negative on a barrel plug?

Yes, it's safe. The DC barrel jack polarity is not a universal standard. You'll find that most things use negative on the outside, but some things definitely change this (guitar pedals for example). ...
JYelton's user avatar
  • 34.1k
11 votes

Would 5.5 x 2.1 mm male plug work inside a 5.5 x 2.5 mm female jack for DC power?

I have tried fitting a 2.1 mm barrel plug in a 2.5 mm jack (by accident or consciously) many times and it has never fit. Both sides are rigid and there is not enough clearance. Size adapters are ...
Kevin Reid's user avatar
  • 7,524
10 votes
Accepted

Do TRS connectors short adjacent contacts during insertion?

Quoting Wikipedia: Heavy-duty  1⁄4 in loudspeaker jacks are rated at 15 A maximum which limits them to applications involving less than 1,800 watts.  1⁄4 in loudspeaker jacks commonly are not ...
Wesley Lee's user avatar
  • 7,914
10 votes
Accepted

Are countries that use 2-pin plugs less safe than countries that use 3-pin plugs given that the earth is missing?

That is actually an interesting question. The truth is... it is complicated. Consider the following three connection systems. simulate this circuit – Schematic created using CircuitLab The ...
Trevor_G's user avatar
  • 46.7k
10 votes
Accepted

What kind of plug is this?

This is a standard NEMA 1-15P plug as used in North America. One blade is large if the plug is polarized, but you rarely see polarized equipment nowadays so it's become rarer to see the polarized plug....
Hearth's user avatar
  • 32.6k
9 votes

Why do EU electrical sockets/plugs have two pins for grounding?

Your claim is not true. EU socket/plug standard is a combination of almost all older standards in the EU. It was design that german DIN standard plugs are somewhat compatible with italian or french ...
Crowley's user avatar
  • 379
8 votes
Accepted

What connector do I need to match my existing test leads?

These are generally standard 4mm banana connectors. The specific ones you show are shrouded ones. They need to be shrouded in order for your multimeter to meet its safety specs. For the male ...
Joren Vaes's user avatar
  • 12.5k
8 votes

Add a passive hardware token using a 3.5mm jack

I would make each "token" an I2C device. Using a tip-ring-ring-shank style jack would give you 4 conductors -- ground, power, data, and clock. Each token would need to have it's own I2C address, and ...
Scott Seidman's user avatar
8 votes

Why do EU electrical sockets/plugs have two pins for grounding?

Two pins is more safe than one pin. And it makes the design symmetric, so it can be connected in any orientation.
Justme's user avatar
  • 149k
8 votes

Recommended mounting hole for coaxial plugs

I think the connectors also have a slot cut out of the part that would go in the hole. This is done to make them asymmetrical. If they were completely symmetrical they would be able to rotate in the ...
user253751's user avatar
  • 12.5k
7 votes
Accepted

Are Micro A USB plugs actually ever used?

Yes. Pretty much ignored in favor of the micro-B. There is no "Micro-A receptacle" since the micro-AB covers both. There were many more orders for micro-B cables than there were receptacles, and ...
mangraft's user avatar
7 votes
Accepted

Why AC power plugs have three pins

To power a device, current has to flow thru it. That means it has to go in one place and come out another, which requires two wires. The third wire of most outlets is a safety ground. It is not ...
Olin Lathrop's user avatar
7 votes
Accepted

Why does this UK mains plug have a gap going down the live pin?

The live pin has a gap because the part on the other side of the plastic forms the fuse clip. The gap will have no affect on the current-carrying capacity of the pin, but the two parts on either side ...
Richard Crowley's user avatar
7 votes
Accepted

Problem with molex connectors

Both manufacturers have assumed that whatever will be plugged into the other end of their connector will have both ground pins fitted & connected together (usually a safe assumption). They ...
brhans's user avatar
  • 14.7k
7 votes
Accepted

Help with identifying a PCB header connector

That header is a Molex 2.50mm pitch SPOX wire to board header system. There are also several other manufacturers that make clones of these. Here is the Molex data sheet for the 4-pin shrouded PC mount ...
Michael Karas's user avatar
7 votes
Accepted

Why are plug tops rated 16A and not 17, 18 or 19A?

This is a 'rating'. A committee somewhere has decided on some (reasonable we hope) standard test conditions, and a limiting temperature for the plug elements. 16A is the current which achieved that ...
Neil_UK's user avatar
  • 167k
6 votes

Stranded wire was cut... Connecting it back together, with solid wire... Is this safe and possible?

That's neither safe nor robust. The solid wire could break after being flexed, and the tape won't reliably hold it together. Perhaps more importantly, simply twisting the wires together without ...
pericynthion's user avatar
  • 6,174
6 votes
Accepted

Why does Macbook (with a alumnum shell) use a 2-prong plug instead of 3-prong plug?

The Macbook has an external power supply that converts AC to DC. The power supply provides the necessary safety and isolation, so you don't need earthing of the Macbook case.
filo's user avatar
  • 8,961
6 votes
Accepted

What is this cable/device?

That's an infrared transmitter for extenders or control systems. That plastic chunk with the IR LED gets glued on a device like TV or Blu-Ray player so that it shines on the device's IR receiver.
Justme's user avatar
  • 149k
6 votes
Accepted

Why are replacement plugs in the US only rated at 125V even though many of our devices can also be run on 220V?

This is a code issue. By code, certain outlets should only be used on a 120 V circuit. And a different outlet should be used on a 240 V circuit. If the 120-V outlet were used on a 240-V circuit, ...
The Photon's user avatar
  • 130k
6 votes
Accepted

Would 5.5 x 2.1 mm male plug work inside a 5.5 x 2.5 mm female jack for DC power?

This must be evaluated on a case by case basis, as sometimes the spring loaded tabs will allow for a few 0.1mm's of play. However, 0.4mm is most likely too far and a the right jack\plug combination ...
Voltage Spike's user avatar
  • 82.7k
6 votes

Would 5.5 x 2.1 mm male plug work inside a 5.5 x 2.5 mm female jack for DC power?

Not all plugs are created equal. Some plugs have full, uniform tubes that have little tolerance, and a nominal 2.5mm center pin will not fit inside one designed for a 2.1mm pin. They look like this: (...
Sara's user avatar
  • 202
6 votes

Add a passive hardware token using a 3.5mm jack

This can be done with a set of resistors and capacitor in parallel, each pair with a different RC product. You would turn the gpio output high for a sufficient time, then turn it to an input and ...
EinarA's user avatar
  • 907
6 votes

Add a passive hardware token using a 3.5mm jack

To be crystal clear. I do not hate the 1-wire token idea. I actually like it. Using 1-wire this way is exactly the kind of thing the 1-wire bus was made for. My concern is that the project is toy ...
Charlie's user avatar
  • 365

Only top scored, non community-wiki answers of a minimum length are eligible