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by Burngate
Mon Feb 18, 2019 10:26 am
Forum: General discussion
Topic: What are the 4 pins for?
Replies: 10
Views: 404

Re: What are the 4 pins for?

mahjongg wrote:
Sun Feb 17, 2019 2:00 pm
This is my "truth", as I see it.
It's also "the truth" on the first picture encountered by someone just getting started, at the top of https://www.raspberrypi.org/help/
by Burngate
Sat Feb 16, 2019 6:40 pm
Forum: Off topic discussion
Topic: Should the Pi Forum switch to Discourse?
Replies: 24
Views: 655

Re: Should the Pi Forum switch to Discourse?

I don't dispute the first of those statements - those who would make that sort of decision are unlikely to do so without first researching the problem, and asking me what I thought would be low on their list of priorities. However, I object, strenuously*, to being called "freeloading", which has neg...
by Burngate
Sat Feb 16, 2019 6:18 pm
Forum: Automation, sensing and robotics
Topic: Fuse between motor driver board and power source?
Replies: 9
Views: 162

Re: Fuse between motor driver board and power source?

Fuses come in many different shapes, sizes, and materials, depending on where they're going to be used. So, here in the UK (your profile doesn't indicate where you are) plug-tops have a fuse that has to be removed from the socket before you can change it. It's got a ceramic body that won't shatter w...
by Burngate
Sat Feb 16, 2019 12:28 pm
Forum: Automation, sensing and robotics
Topic: Fuse between motor driver board and power source?
Replies: 9
Views: 162

Re: Fuse between motor driver board and power source?

Why is it that rechargable batteries provide more current or in other words why do they have a lower internal resistance? You want a lesson in chemistry? Primary cells are designed to hold their charge for long periods so they don't have to be replaced too often, and the circuits they feed are gene...
by Burngate
Sat Feb 16, 2019 10:54 am
Forum: Troubleshooting
Topic: The Big (little) Yellow Bolt of Doom
Replies: 21
Views: 435

Re: The Big (little) Yellow Bolt of Doom

Finally davidcoton and mahjongg, i have seen this on a few different web site but I am a bit confused do i just test on any old 5 volt and ground pins or is there a pin pair i should be testing on the GPIO? ... measurement of the on-board voltage at the GPIO header. The major voltage drops will be ...
by Burngate
Thu Feb 14, 2019 10:07 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 106
Views: 1976

Re: Resistors and MOSFETs and fire-prevention, oh my

tlfong01 wrote:
Thu Feb 14, 2019 2:49 am
Gavinmc42 wrote:
Wed Feb 13, 2019 11:20 am
Fet datasheet can lie none are easy to read
I have never heard of the phrase "can lie none".
Can I assist with the punctuation?
Fet datasheet can lie; none are easy to read
by Burngate
Wed Feb 13, 2019 11:06 am
Forum: Beginners
Topic: Power Supply for multiple 12V devices
Replies: 5
Views: 92

Re: Power Supply for multiple 12V devices

If it's really what it purports to be - it can maintain its output at 12v for any current from 0 to 8A - then, yes.

But ... in the picture, the output wires seem awfully thin ...
by Burngate
Wed Feb 13, 2019 10:23 am
Forum: Automation, sensing and robotics
Topic: Ultrasonic sensor and voltage division
Replies: 18
Views: 337

Re: Ultrasonic sensor and voltage division

All this about R2 on its own not changing the voltage - but no-one has said it's because the 5v supply is a source of constant voltage It's designed to keep its terminals 5v apart whatever you do (within reason) and the Echo pin just gets connected to it when necessary You can get constant current s...
by Burngate
Tue Feb 12, 2019 12:09 pm
Forum: Automation, sensing and robotics
Topic: Ultrasonic sensor and voltage division
Replies: 18
Views: 337

Re: Ultrasonic sensor and voltage division

This convention to assume that the current goes from - to + when it physically the other way around is something I don't really understand. :? Blame the 18th & 19th century physicists for this. They could see strange things happening when they connected differing metals, with chemicals between them...
by Burngate
Thu Feb 07, 2019 7:11 pm
Forum: Beginners
Topic: detect a low (1.5v) signal on GPIO?
Replies: 4
Views: 105

Re: detect a low (1.5v) signal on GPIO?

Collector of the transistor connected to 3.3v and a GPIO pin and emitter to ground. I'd add a few resistors to the mix. You don't want to connect collector directly to 3v3 and emitter to ground - when the transistor switches on, it'll short out the 3v3. 3v3 - resistor - GPIO and collector, emitter ...
by Burngate
Thu Feb 07, 2019 7:02 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 106
Views: 1976

Re: Resistors and MOSFETs and fire-prevention, oh my

The question still is, 2 grounds?...going to the same place? I feel like these should be 2 separate circuits...1) the gate and 2) the source/drain. That T is very strange to me. There's only one ground - because "ground" is the point of reference for all voltage measurements. As an output, a GPIO w...
by Burngate
Thu Feb 07, 2019 6:30 pm
Forum: General discussion
Topic: Pi 3A+ Schematic question
Replies: 6
Views: 225

Re: Pi 3A+ Schematic question

Missing from the 3B+ sheet but present on the 3A+ sheet is the arcane invocation "Make ADC traces accessible before shorting to GND" Also, I don't quite understand what AGND is for, since it doesn't appear anywhere other than round the PMIC, and not where I would have expected, at the audio subsystem.
by Burngate
Wed Feb 06, 2019 7:14 pm
Forum: General discussion
Topic: Physical port widths on B+
Replies: 21
Views: 481

Re: Physical port widths on B+

In my youth, I was occasionally tasked with marking out the pitch for our team, using (yes!) a steel chain of the appropriate length. Was that borrowed from the Geography department? Somewhere I've got a book about the mapping of India. They started on the shore on the south coast, with a steel cha...
by Burngate
Wed Feb 06, 2019 7:08 pm
Forum: Troubleshooting
Topic: Pi 3 Model B+, strange problems with power
Replies: 10
Views: 238

Re: Pi 3 Model B+, strange problems with power

Just out of interest, has the Ubuntu image been updated for the 3B+?
I only ask, because there was a bit of confusion caused by ACT and PWR LEDs swapping places between revisions of the Pi, leading to the lightning symbol appearing when it shouldn't.
by Burngate
Wed Feb 06, 2019 6:26 pm
Forum: Troubleshooting
Topic: Low voltage warning on boot
Replies: 24
Views: 624

Re: Low voltage warning on boot

... the system should, surely, be able to tolerate different qualities and capabilities of cables, connectors, extensions and PSUs. I've been thinking about this since you wrote it, and I've come to the conclusion that it does tolerate these things, provided they, together, meet the minimum spec. o...
by Burngate
Tue Feb 05, 2019 6:22 pm
Forum: Raspbian
Topic: New HELP ideas
Replies: 18
Views: 475

Re: New HELP ideas

PhatFil wrote:
Tue Feb 05, 2019 4:48 pm
Alarm bells anyone??
No.
Brexit will (maybe) happen then, but the sounding of trumpets isn't time-critical.
It'll happen when it happens, just like Pi 4
by Burngate
Tue Feb 05, 2019 6:16 pm
Forum: C/C++
Topic: Hardware Watchdog Issue with GPIO
Replies: 1
Views: 182

Re: Hardware Watchdog Issue with GPIO

Note: I haven't got one of these, so this is theoretical. Looking at the SwitchDoc site, there appears to be two versions; the one called "Version 110216-01-001" has "Open Drain buffers added to the Grove Watchdog inputs" whatever that means, so "You no longer have to leave the inputs float for the ...
by Burngate
Mon Feb 04, 2019 7:10 pm
Forum: Troubleshooting
Topic: Low voltage warning on boot
Replies: 24
Views: 624

Re: Low voltage warning on boot

... when is a PSU an actual PSU as opposed to a charger? Like many things, it probably depends on who's talking. But the way I would use the terms, what you connect to your phone is a charger, because its primary purpose is to charge the battery - the phone uses its battery as its power supply. The...
by Burngate
Mon Feb 04, 2019 6:54 pm
Forum: HATs and other add-ons
Topic: Official Raspberry Pi power supply -- adding power switch
Replies: 8
Views: 732

Re: Official Raspberry Pi power supply -- adding power switch

Disclaimer: I'm probably out of my tree, if not actually wrong.

The pictures show a mains connection I'm not familiar with, but seems to be reversible.
If that's true, what happens if you reverse it?
by Burngate
Mon Feb 04, 2019 12:00 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 106
Views: 1976

Re: Resistors and MOSFETs and fire-prevention, oh my

danjperron wrote:
Sun Feb 03, 2019 6:38 pm
Capture d’écran 2019-02-03 à 13.37.19.png
Just a note: This diagram is far nicer than mine, and better than any I've seen done in Fritzing.
So it might be worth asking what program he's using
by Burngate
Sun Feb 03, 2019 11:41 am
Forum: Off topic discussion
Topic: Why I love my PIs
Replies: 32
Views: 1090

Re: Why I love my PIs

IT guys tend to be quite conservative - they know a Windows tower works, they know the users know how to use it, and when things go wrong they know how to fix it quickly, even if that means spending money on a new tower. The Pi is priced low, so that when things go wrong it's not too costly to repla...
by Burngate
Sun Feb 03, 2019 10:02 am
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 106
Views: 1976

Re: Resistors and MOSFETs and fire-prevention, oh my

The resistor between GPIO and gate: large enough that current from the GPIO is lower than it can handle. Since the GPIO can't provide more than ~15mA and 3v3, Ohms law says more than 220 ohms. 1k would be enough. So would 470 or 330, depending on what you have in your bits-box. For the resistor from...
by Burngate
Sat Feb 02, 2019 7:08 pm
Forum: Beginners
Topic: Resistors and MOSFETs and fire-prevention, oh my
Replies: 106
Views: 1976

Re: Resistors and MOSFETs and fire-prevention, oh my

A couple of things. You're labelling the pins of the MOSFET as middle = Source, right, and gate. But the datasheet you linked to has two drawings - TO-220AB & TO-263AB - neither of which has the source in the middle, so I'm confused. From your description, I think you have: _________ +12V | | | --- ...
by Burngate
Fri Feb 01, 2019 7:09 pm
Forum: General discussion
Topic: MOSFET IRF520
Replies: 8
Views: 260

Re: MOSFET IRF520

As far as I'm aware, controlling mains devices such as these is normally done using triacs with phase-control rather than PWM Firing the triac part-way through each half-cycle limits the time current flows, hence the power. Before you try that at home, it's worth while finding out how to keep the ma...
by Burngate
Fri Feb 01, 2019 6:44 pm
Forum: General discussion
Topic: How many pieces of pi are too many?
Replies: 72
Views: 2016

Re: How many pieces of pi are too many?

One of the interesting differences between Neanderthals and "us" is that "they" made multipurpose stone tools, while "we" made lots of different sorts of specialist ones. Of course "them" and "us" is an artificial dichotomy - unless all your ancestors remained in southern Africa you've probably got ...

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