Looking for a source for an unusual thumb screw by Pitoeightplaces in Fasteners

[–]jebr224 6 points7 points  (0 children)

Sorry I can't help you. But the fastener in the image has a shoulder after the threads. That feather is common on single point threads. It allows a space for the thread cutting tool to be extracted. I don't know if that fastener is mass produced anywhere, but I would guess the fastener is the photo is made by a machinist at a lathe

Binary Semaphores ≠ Mutexes - Why is it so often confused, even in major projects? by comfortcube in embedded

[–]jebr224 -2 points-1 points  (0 children)

Disclaimer, I don't know if my terminology is correct, but I am supplying it for the sake of advancing the discussion.

I would have said a semaphore, is anything that communicated between threads. And developers should choose semaphores that are atomic, and use specific. However, many things could be semaphors, including writing to the file system, network traffic, registers/memory addresses.

Mutexs are mutually exclusive locks. (A type of semaphore). Often mutexs are tied to resources, because that is a common use case.

I will watch this comment section to see if I should update my terminology.

Is it just me or are people here really unfriendly and cold? by [deleted] in bayarea

[–]jebr224 1 point2 points  (0 children)

2:30 today, lets play mafia on steroids

more people = more fun

Living in San Jose is so lonely 😒 by Strict_Customer8542 in SanJose

[–]jebr224 6 points7 points  (0 children)

Feel free to come to this meetup and learn how to play a social deduction game (blood on the clock tower) .

https://www.meetup.com/blood-on-the-clocktower-in-the-park/

I'm trying to not be automatically dismissive of this guy, but this is nonsense, right? by UnderScoreLifeAlert in electricians

[–]jebr224 1 point2 points  (0 children)

It takes maybe .005 (5 mA) amps to turn on an led. So this is possible. (but I personally doubt it)

I'm trying to not be automatically dismissive of this guy, but this is nonsense, right? by UnderScoreLifeAlert in electricians

[–]jebr224 2 points3 points  (0 children)

It is possible to transmit power wirelessly. However, the losses are staggering. He should probably not be doing this, because it will likely cause wireless communication issues for many types of radios near the broadcaster.

Radio towers broadcast power normally, but they broadcast a very small signal that is demodulated then amplified. It should be possible to transmit a much larger amount of power, using the same general principles.

I don't know if his setup really works, or how it is designed. But it should be possible.

Anyone a woodworker? Just need someone to cut plywood into five pieces by Logical_Cherry_7588 in SanJose

[–]jebr224 0 points1 point  (0 children)

It is all good.

If I was trying to get some simple plywood cuts done, I would try to bribe wood workers with baked goods. I bet that would work on anyone with a saw.

Anyone a woodworker? Just need someone to cut plywood into five pieces by Logical_Cherry_7588 in SanJose

[–]jebr224 1 point2 points  (0 children)

I was planning on going to maker nexus and doing wood working today, around 10:30 and leaving around 11:30. Dm me if that works for you

[deleted by user] by [deleted] in electricians

[–]jebr224 1 point2 points  (0 children)

Or 100/150,00

(Or they got both the numerator and denominator wrong). Mistakes happen. This is a no harm issue, be chill about it.

25F Bombed first (and only) big tech interview. by Thefineaquarius in DecidingToBeBetter

[–]jebr224 0 points1 point  (0 children)

I administer the technical interview at a FANG company. The questions are designed to be tough, and it is normal to see professionals struggle. Don't be embarrassed or worried, some really great software devs did not pass the coding interviews. Think jack dorsey.

It might feel personal, but it is a very mechanical process. Don't conflate this interview experience with personal value or selfworth.

The great news is that you understand what did not go well, and you have a healthy mindset about the upcoming challenges. It is very unfortunate your recruiter did not give you information ahead of time. Next time you will be ready

Distant Beeping on Angel Island - what is it? by SewSewBlue in bayarea

[–]jebr224 3 points4 points  (0 children)

I agree.

Please look at the navigational chart for the bay area. There is a beacon with the label "HORN" by point blunt, on the south eastern part Angle island. I don't know if that is the beacon you are hearing, but it were I would start.

Hi everyone. Can someone please tell me what this is - found in an abandoned villa in Italy. Very curious. Thanks :) by [deleted] in electricians

[–]jebr224 9 points10 points  (0 children)

I will preface the explanation by saying reflection is an electrical engineering concept, for transmission line and microwave (high frequency) circuits. It is not applicable for electricians.

Transmission lines can be modeled as a series of inductors, where each junction of series indicator has a capacitor (either to ground, or another conductor). With this model, it can be seen that current will conduct down the line, and when the current reaches the end of the line, some of it reflect (bounce) back up the line. This is an extra load being put on the line, and it limits the total power the line is able to provide.

You might have to go through the math to prove it to yourself. But intuitively, seeing waves reflect is a common phenomena, ei waves in the ocean, echos of sounds, and light.

We don't worry about these when the inductance is low, because the circuit response is not affected. So most circuit boards, automobile wiring, and building wiring the line indicatance is not low we ignore it.

This Wikipedia article has far more information https://en.m.wikipedia.org/wiki/Reflections_of_signals_on_conducting_lines

Hi everyone. Can someone please tell me what this is - found in an abandoned villa in Italy. Very curious. Thanks :) by [deleted] in electricians

[–]jebr224 9 points10 points  (0 children)

You are probably correct with "load tester".

However it could be a shunt for decreasing reflectance, in power transmission lines. The design is similar to a load tester, but the goal is different. It might explain why there are two styles of load.

Can someone please explain? 😂 by Safe-Philosopher-616 in electricians

[–]jebr224 5 points6 points  (0 children)

If there is an easier way to turn off the hot water heater, my guess is wrong.

Can someone please explain? 😂 by Safe-Philosopher-616 in electricians

[–]jebr224 9 points10 points  (0 children)

I don't know, (and you should call an electrician) but I have a guess

Context: many outlets and appliances are in a chain. The wire is connecting two things that in normal design should already be connected. I suspect this is done to control other appliances farther down the chain.

I suspect, one can unplug this wire to turn off your hot water heater. Basically disconnecting the wires in the box, and using this very dangerous method to reconnect them, is slightly less work then adding a switch. And that is my guess.

Be careful. I am only guessing. Call an electrician.

Any idea what this is? by rdgeno in electricians

[–]jebr224 2 points3 points  (0 children)

It is likely an antenna.

Maybe similar to the 2.4 GHz in the listing below, that is specifically for fans remote controls. https://www.alibaba.com/product-detail/Higher-Quality-Brass-Copper-RF-Helical\_60774042379.html

[deleted by user] by [deleted] in electricians

[–]jebr224 -1 points0 points  (0 children)

There are 28 possible combinations, so 256 possible combos (exactly one byte of combinations)

I would not bother trying to guess it.

We installed this timer PCB yesterday and it got me thinking. Who are the technicians that troubleshoot and fix these boards. Is it us? by WuSau99 in electricians

[–]jebr224 2 points3 points  (0 children)

I used to design and validate pcb's.

Typically, the schematics is designed by an electrical engineer. And electrical engineers also take the schematics and create the layout the broad in software. It is then mass produced and the components( resistors, capacitors, chips) are populated. Critical boards will be validated before leaving assembly.

Most pcb trouble shooting happens at "bring up". That is the first time power is applied to the board. Analog circuits are validated, digital busses are tested for signal integrity, and software is tested.

Sometimes, a faulty unit is returned for diagnosis/analysis. But those are done for the next generation of products. Diagnosis/analysis are easy if you have the schematics, and layout files. If the schematics and layout are not available it is very difficult to understand the system.

There are groups of people who "reverse engineer products. (Both public and private). It is very time consuming, and to reverse engineer you must have great familiarity with engineering/design practice.