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 detected, for example using bash command:
and checking it's output for existence of subdirectory named exactly as this hardware address.
Wireless technology is great and can be used in all sorts of scenarios but it's complex and hard to design for. Wires are in fact superior in many ways.
( Taken from: Essentials of Short Range Wireless Standards )
Range is not an issue - just add more cable
Latency is excellent - what goes in one end appears immediately at the other
Wired connections have some properties that wireless connections don't:
Robustness: a wireless connection can be subject to various forms of interference (think to microwave ovens) and obstacles, that can affect the quality of the received signal.
Latency: wireless connections make a large use of acknowledge signals and error checking codes, due to their ...
What you're talking about I use every day: my PC is wireless connected with my router and can transceive data at 300 Mbps. Works fine. Ten years ago I used a CAT-5 cable for that (a bit lower speed back then).
But there's cost. A few meter of wire will probably be cheaper, especially at low speeds, when there aren't that strict requirements for the cable.
Tin both wire ends first. Fill the middle cup with solder, and stuff the (stripped) positive wire in while the solder is hot. Push the negative wire through the hole from inside to outside up to the insulation, and solder the wire to the outside of the contact towards the plug. Crimp the arms around both (insulated) wires. Screw the cap on (and oh yeah, don'...
And you often hear about people being killed by testing batteries with their tongue,
The chances of such reports being true are close to zero.
I have never heard of such a report that is reputable or traceable to source*.
I cannot think of a mechanism that would make doing this likely to be fatal.
I do not recommend that others do this without ...
A plug doesn't have polarity, it completely depends on the wiring of the socket. To check the socket all you need is this two dollar tester:
It has a neon light inside which connects via a high resistance to the contact at the end. If you insert in in the live pin and touch the metal dingus on the back of the tester, there will flow a very small, safe,...
I suppose since the earth prong is also longer on these BS 546 plugs, if you could partially plug it in the wrong way (say earth to phase), then someone else touching the appliance at the same time could receive a shock. So the earth prong is thicker so that you cannot plug it in even a little bit in the phase/neutral holes. (Rotational asymmetry would ...
From the look of the wires, I'd say that they are a speaker cable, and the gold pin is just to make it easier to insert the wire ends into binding posts or the wire clips that many speakers have. Are there similar wires (with or without the gold pin) elsewhere in the room (or elsewhere in the house)?
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 rigged to lock the plug in place and will short out the amplifier's output circuitry if connected or disconnected when the amplifier is live.
A disadvantage ...
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.
As for the blade spacing, there's a fair amount of play in American plugs and sockets. The spacing can be off by a bit without it really mattering, and the ...
Even tough it may resemble one, this is NOT a banana plug:
It is a 2.5mm pin plug or 2.5mm male pin connector.
It is appropriate for low DC (<=60V) or AC (<=30Vrms) voltages and up to a relatively high amount of current, possibly up to 10-15A, depending on the mating subtype and quality of manufacturing.
It usually comes in two variants:
Those where ...
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 first is your typical appliance with a three pin plug and a grounded case. If there is a short from the live line to the case the line is shorted out and ...
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 connectors, standard connectors can be used in jacks designed to take shrouded ones. In the other direction, this is not the case - a shrouded plug cannot go into a ...
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 you would write a function that sniffs out devices on an I2C bus.
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 necessary to power a device, but can be useful to some devices. Any device that has a conductive outer shell is a potential safety hazard. It would only take one ...
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 therefore assume that they can save 1 or 2c on each unit by only fitting 1 ground pin.
Unfortunately for you, they each picked a different pin to fit.
If you have any ...
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 of the gap form the fuse clip as your photo shows very nicely. Clever design.
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 header. http://www.mouser.com/ds/2/276/0099990988_PCB_HEADERS-137537.pdf
This particular one has inline pins for through hole mount. There are also versions ...
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 solder or the pressure of a crimp or screw terminal will not give a low-resistance, gas-tight joint. The resistance will likely increase over time as the conductors ...
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 temperature under those conditions.
This obviously begs the question of why those conditions, and why that temperature.
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 available; I recommend having some around for use when you have a device that doesn't come with a power adapter and an adapter with the right voltage. They do have ...
I admit that this type of plug is almost impossible to solder well. The center pin is not much of a problem, just strip a very short patch of one wire (center wire of course, if you have a coax-style cable) and solder it.
For the outer tab you can heat it for some time until solder flows over the desired place, then press the pre-tinned wire onto the ...
We can only speculate.
I had my other hand against the nearby wall corner,
Walls are usually not that conductive, it is likely that this was an important factor.
I had only 2 fingers in there, one against each rod
If you had a separate finger against each pin of the plug, I'd expect the majority of the current to flow through your hand. From the fact ...
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 the industry quickly scrapped the micro-A.
That connector is a single gold-plated crimp-on speaker pin.
The other lead used to have an identical connector, and the pair was plugged into a single speaker. That speaker was ripped off the wall without disconnecting the wire, and the pin you don't see stayed stuck in the speaker's input terminal.
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, somebody could plug in a device that isn't rated for 240-V. This would likely damage the device, and could cause further damage like starting a fire or ...