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by achrn
Tue Oct 20, 2020 3:08 pm
Forum: General discussion
Topic: external power supply samsung power bank
Replies: 22
Views: 681

Re: external power supply samsung power bank

To complete the pendantry... P=vi is only true for Direct Current (DC). For Alternating Current (AC), you need to multiply by 0.7 (actually 1/sqrt(2)) to get the root mean square (RMS) value. "0.7 (actually 1/sqrt(2)) to get the root mean square (RMS) value" would be to convert a peak voltage or a ...
by achrn
Tue Oct 20, 2020 7:08 am
Forum: General discussion
Topic: Reliable power-off detection for Pi Zero
Replies: 15
Views: 488

Re: Reliable power-off detection for Pi Zero

GPIO27 works for me on a Pi3 (I don't recall if I've tested it on an actual zero). It goes low on poweroff, though it needs to be set high in the first place (I have that in a script running soon after boot). Other alternatives are listed in the peripherals data sheet https://www.raspberrypi.org/app...
by achrn
Fri Oct 16, 2020 12:48 pm
Forum: General discussion
Topic: Power Multiple Devices including RaspberryPi 4, LED, Speaker etc, using single 12v 3A input
Replies: 7
Views: 257

Re: Power Multiple Devices including RaspberryPi 4, LED, Speaker etc, using single 12v 3A input

https://www.ebay.co.uk/sch/i.html?_nkw=hobbywing+ubec+3a In my testing the Hobbywing 3A UBEC does deliver 3A reliably. I haven't actually run a 4B off one of these very long, but they do deliver 3A for me. If you don't trust it, any other suitable specced non-isolated POL DC-DC convertor will do it....
by achrn
Fri Oct 09, 2020 7:32 am
Forum: General discussion
Topic: What about heat issues on Raspberry Pi 4 Model B ?
Replies: 35
Views: 1238

Re: What about heat issues on Raspberry Pi 4 Model B ?

Heater wrote:
Fri Oct 09, 2020 6:04 am

Something does not add up here.
Bernoulli assumes no energy is added to the system.
A fan adds energy.
by achrn
Mon Oct 05, 2020 3:20 pm
Forum: General discussion
Topic: can i use a 2.1 amp power cord for pi 4
Replies: 37
Views: 810

Re: can i use a 2.1 amp power cord for pi 4

I wonder why the manufacturer of your RPi board would publish a Specification that says 5V DC via USB-C connector (minimum 3A*) if something of far lower capability would suffice? As a matter of fact something lower than 3A does suffice in many cases. Whether teh particular supply in question will ...
by achrn
Sun Oct 04, 2020 5:38 am
Forum: General discussion
Topic: Power efficiency of official power supply?
Replies: 8
Views: 576

Re: Power efficiency of official power supply?

I am quite concerned at the relatively low load regulation figure of 5%, this means the 5.1V supply might not achieve 4.85V at full load. When I tested an older official PSU it showed a linear characteristic from about 5.2V at 200mA to 4.7V at 3.4A, so at 2A it was about 4.95V. My write-up is at ht...
by achrn
Mon Sep 28, 2020 6:58 am
Forum: General discussion
Topic: Pi server with UPS
Replies: 1
Views: 90

Re: Pi server with UPS

It is certainly possible. The most recent similar thread (that I've noticed) is https://www.raspberrypi.org/forums/viewtopic.php?f=63&t=281334. There are previous threads. What I built (which is an approach, but not the only approach) is written up at http://www.astounding.org.uk/ian/raspi-ups/index...
by achrn
Sun Aug 23, 2020 5:01 pm
Forum: Off topic discussion
Topic: Help..I know nothing about RPi and I'm in need of help (not what you think)
Replies: 3
Views: 579

Re: Help..I know nothing about RPi and I'm in need of help (not what you think)

It's going to be really difficult to hide a raspberry pi inside a laptop to steal anything - it would be easier to just sit outside the house and steal from there, so it's quite unlikely to be that. Is the supposed Pi still active (does your monitoring thing tell you the last time it saw traffic)? C...
by achrn
Thu Aug 20, 2020 6:36 am
Forum: General discussion
Topic: RPi 4 12V pwm fans - Schematic
Replies: 16
Views: 790

Re: RPi 4 12V pwm fans - Schematic

With the original circuit he will not see much at all as the diode is back-to-front. I wonder if that's why I said "I'd use a bipolar tansistor, i.e. your first circuit ( but without the diode )"? I don't know, there was no explanation. That error in the circuit has already been discussed. For exam...
by achrn
Wed Aug 19, 2020 7:36 pm
Forum: General discussion
Topic: RPi 4 12V pwm fans - Schematic
Replies: 16
Views: 790

Re: RPi 4 12V pwm fans - Schematic

pidd wrote:
Wed Aug 19, 2020 9:51 am
With the original circuit he will not see much at all as the diode is back-to-front.
I wonder if that's why I said "I'd use a bipolar tansistor, i.e. your first circuit (but without the diode)"?
by achrn
Wed Aug 19, 2020 7:03 am
Forum: General discussion
Topic: RPi 4 12V pwm fans - Schematic
Replies: 16
Views: 790

Re: RPi 4 12V pwm fans - Schematic

If the fan pulls its line up to 6.39 open circuit I wouldn't connect it direct to the GPIO (there is a possibility that you won't damage teh Pi, but you really don't want to apply more than 3.3V to a GPIO pin). So yes, I'd use a transistor to drive the PWM wire. I'd use a bipolar tansistor, i.e. you...
by achrn
Sat Aug 15, 2020 5:09 pm
Forum: General discussion
Topic: RPi 4 12V pwm fans - Schematic
Replies: 16
Views: 790

Re: RPi 4 12V pwm fans - Schematic

OK. So that says it does have a PWM input (yellow wire) with a voltage high level of between 2.8V and about 20V, and low level has to be below 0.8V. It doesn't specify if the fan pulls this line up itself, or how it pulls it up (i.e. how strong), so first thing I'd do is connect up the power supply ...
by achrn
Sat Aug 15, 2020 4:09 pm
Forum: General discussion
Topic: RPi 4 12V pwm fans - Schematic
Replies: 16
Views: 790

Re: RPi 4 12V pwm fans - Schematic

This circuit will try and apply a 3.3V signal to the fan pin 2, but as previously noted, without knowing anything about the fan, whether that will actually achieve anything is anyone's guess. Also, if the fan pulls up its pin 2 above 3.3 V, you're going to pull the Pi's 3.3 volt line up too, which m...
by achrn
Fri Aug 14, 2020 9:19 pm
Forum: General discussion
Topic: RPi 4 12V pwm fans - Schematic
Replies: 16
Views: 790

Re: RPi 4 12V pwm fans - Schematic

I don't know what fans you're using but a 3 wire fan is generally power supply and tacho (or locked rotor signal). You can't control it by doing anything to the tacho line. A normal PC 4 wire fan, the PWM control is pin 4 (1 is ground, 2 is 12V, 3 is tacho, 4 is PWM). If what you have is not standar...
by achrn
Fri Aug 14, 2020 12:03 pm
Forum: General discussion
Topic: SCP - can't find the file
Replies: 5
Views: 269

Re: SCP - can't find the file

If I try to connect to ssh with this command: ssh 192.168.0.222 It asks me to enter the password, I do and I get warranty statement. Then when I try this command again (exact same command): scp /home/pi/weather-station/weather-monitor.pkl pi@192.168.0.222:/home/pi/weather-station/test2.pkl It says ...
by achrn
Mon Aug 10, 2020 7:17 am
Forum: General discussion
Topic: How to drive Brushless DC motor with built in driver and no documentation?
Replies: 21
Views: 1077

Re: How to drive Brushless DC motor with built in driver and no documentation?

But before buying extra components, why not just stick a highish frequency PWM on the input and see if it works with no extra circuitry? Depending what's inside the controller (ie it may already have a low pass filter), extra gubbins outside the motor possibly achieves nothing. Since the manufactur...
by achrn
Sat Aug 08, 2020 8:03 am
Forum: General discussion
Topic: How to drive Brushless DC motor with built in driver and no documentation?
Replies: 21
Views: 1077

Re: How to drive Brushless DC motor with built in driver and no documentation?

But before buying extra components, why not just stick a highish frequency PWM on the input and see if it works with no extra circuitry? Depending what's inside the controller (ie it may already have a low pass filter), extra gubbins outside the motor possibly achieves nothing. Since the manufacture...
by achrn
Thu Aug 06, 2020 8:47 am
Forum: General discussion
Topic: How to drive Brushless DC motor with built in driver and no documentation?
Replies: 21
Views: 1077

Re: How to drive Brushless DC motor with built in driver and no documentation?

i'm thinking it might be a bit of both, the PWM signal is ran thru a low-pass filter to make it into an analog level, which then sets the speed so you can then use either a dumb pot, or a PWM from something digital, but you need higher duty cycles, like clicky said it may also need a level shifter,...
by achrn
Tue Aug 04, 2020 10:01 am
Forum: General discussion
Topic: ARE THE HIGH QUALITY SENSORS FOR RPi?
Replies: 9
Views: 503

Re: ARE THE HIGH QUALITY SENSORS FOR RPi?

I wonder if you guys have suggestions on where to source high quality for the RPi, with which decent and reliable measurements can be made. I ask this because to my experience the commonly found sensors for RPi are basically (and apologies for my expression) crap. Don't buy your sensors on ebay - m...
by achrn
Thu Jul 30, 2020 9:27 pm
Forum: General discussion
Topic: Poor Man's Pi Safe Backup Supply (UPS)
Replies: 51
Views: 3933

Re: Poor Man's Pi Safe Backup Supply (UPS)

I'd add a resistor and a diode and trickle recharge the batteries all the time the power is on. Do not do that. I'm no battery expert but from what I read here and elsewhere this is a very bad idea: https://batteryuniversity.com/learn/article/charging_nickel_metal_hydride#:~:text=It%20is%20difficul...
by achrn
Thu Jul 30, 2020 10:47 am
Forum: General discussion
Topic: Poor Man's Pi Safe Backup Supply (UPS)
Replies: 51
Views: 3933

Re: Poor Man's Pi Safe Backup Supply (UPS)

I'd add a resistor and a diode and trickle recharge the batteries all the time the power is on. See http://www.astounding.org.uk/ian/raspi-ups/index.html . I posted that circuit to these forums some years ago, and even then it was pointed out that someone else had done it before me. The dtoverlay ad...
by achrn
Wed Jun 24, 2020 6:54 pm
Forum: General discussion
Topic: Advice for yet another home energy monitor
Replies: 9
Views: 498

Re: Advice for yet another home energy monitor

When I wanted an accurate current value I used an arduino that sends its results to the Pi. The electrical current sensor is just a five amp ACS712 breakout board from ebay, connected to one of the analogue inputs on the Arduino. The arduino calculates the RMS calc too: Rather than anything clever I...
by achrn
Fri Jun 12, 2020 5:19 pm
Forum: General discussion
Topic: Storage recommendations
Replies: 10
Views: 745

Re: Storage recommendations

Can you tolerate any data loss? How many decades are you planning on it running? Surely your data rate is so low that if you cut down the system logs then you probably only use each bit of card memory once in a couple of decades of running? I'd just use a reputable (I stick to Sandisk ultra A1) but ...
by achrn
Mon Jun 01, 2020 1:56 pm
Forum: General discussion
Topic: Notepad++
Replies: 51
Views: 5046

Re: Notepad++

Notepadqq is not quite as good as notepad++ (in my opinion - I use notepadd++ on Windows and notepadqq on linux) but is at least written in linux-firlendly source. I'm not aware of a Pi package for it, but in principle you could compile it for Pi.
by achrn
Fri May 22, 2020 8:51 am
Forum: General discussion
Topic: 110V DC for USB-C Power Supply for Raspberry Pi 4
Replies: 27
Views: 1599

Re: 110V DC for USB-C Power Supply for Raspberry Pi 4

DFM wrote:
Thu May 21, 2020 1:07 pm
The only problem is that the new Raspberry Pi 15.3W USB-C Power Supply does not seem to support an 110V DC input. However, the 110V DC are the only voltage supply that we can use.
Out of curiosity, where do you only have 110V DC?

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