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by davidcoton
Thu Feb 27, 2020 3:37 pm
Forum: Advanced users
Topic: Powering my RPi projects using buck converters
Replies: 9
Views: 228

Re: Powering my RPi projects using buck converters

The polyfuse (on Pi1, 2, 3 models) will protect the TVS diode, so should you apply the wrong voltage through supply fault or user error, the polyfuse may trip before the TVS melts. The anecdotal evidence is that the TVS usually fails SC, which is a repairable fault. However, on the Pi4 (or earlier m...
by davidcoton
Thu Feb 27, 2020 3:20 pm
Forum: Beginners
Topic: Connecting of 12V with PWM regulator to GPIO pins?
Replies: 5
Views: 118

Re: Connecting of 12V with PWM regulator to GPIO pins?

drgeoff wrote:
Thu Feb 27, 2020 12:40 pm
davidcoton wrote:
Thu Feb 27, 2020 11:53 am
The FET converts the 3V3 GPIO signal to 12V for the fan.
That is badly worded.

The 3.3 volt PWM GPIO signal causes the FET to switch on and off the 12 volt supply to the fan.
Thanks for the clarification.
by davidcoton
Thu Feb 27, 2020 3:16 pm
Forum: General discussion
Topic: Raspberry Pi 4B 2GB Price Drop - NOW $35
Replies: 36
Views: 1673

Re: Raspberry Pi 4B 2GB Price Drop - NOW $35

drgeoff wrote:
Thu Feb 27, 2020 3:12 pm
jamesh wrote:
Thu Feb 27, 2020 12:22 pm
I don't think I've ever run out of memory on a 4GB Pi TBH.
I'm sure that if there is ever an 8Gbyte RPi4B there will be badly written software which doesn't run comfortably in 8 Gbyte.
FTFY :roll:
by davidcoton
Thu Feb 27, 2020 11:53 am
Forum: Beginners
Topic: Connecting of 12V with PWM regulator to GPIO pins?
Replies: 5
Views: 118

Re: Connecting of 12V with PWM regulator to GPIO pins?

Doesn't Google work for you? Try this discussion of suitable FETs and how to drive them (ignore the bipolar (bjt) options).

The Pi itself will generate the PWM signal, using the PIGPIO library or similar. The FET converts the 3V3 GPIO signal to 12V for the fan.
by davidcoton
Thu Feb 27, 2020 10:59 am
Forum: Beginners
Topic: Connecting of 12V with PWM regulator to GPIO pins?
Replies: 5
Views: 118

Re: Connecting of 12V with PWM regulator to GPIO pins?

The answer is mainly software. Find or write a service to generate a PWM (on a GPIO pin) proportional to temperature (with appropriate upper and lower limits). Shout here if you get stuck. For hardware, use a FET with a low enough gate voltage to work from the GPIO (3V3). That can drive a 12V fan. Y...
by davidcoton
Tue Feb 25, 2020 3:56 pm
Forum: Troubleshooting
Topic: [SOLVED]USB overcurrent warning
Replies: 6
Views: 208

Re: USB overcurrent warning

You can take the power from the downstream (GPIO header) side of the polyfuse.

If your existing PSU is adequate (and it might not be when the 1A2 restriction on USB load is removed), it would be better to arrange power routing external to the Pi by modifying (or making alternative) cables.
by davidcoton
Tue Feb 25, 2020 3:49 pm
Forum: Beginners
Topic: Please help me understand the clock pin of Serial RS232 communication
Replies: 27
Views: 442

Re: Please help me understand the clock pin of Serial RS232 communication

There is potentially another serious compatibility issue. The device is using a 9V supply, but what voltage is used on the Data (and Clock) outputs? Pi GPIOs expect 3V3 signal, 9V will probably cause permanent damage to your Pi. (Incidentally even if you have a true RS232 device, the Pi will not tol...
by davidcoton
Tue Feb 25, 2020 10:44 am
Forum: General discussion
Topic: RaspPi 4 WiFi Range?
Replies: 10
Views: 381

Re: RaspPi 4 WiFi Range?

I don't know the range, but the usage precludes 5GHz as that is not licenced for outdoor use (IIRC).
by davidcoton
Mon Feb 24, 2020 9:49 am
Forum: Beginners
Topic: What are the advantages and disadvantages of Arduino and Raspberry Pi?
Replies: 12
Views: 355

Re: What are the advantages and disadvantages of Arduino and Raspberry Pi?

Depends entirely on what you want to achieve with them. Give us more info to work with.
by davidcoton
Sat Feb 22, 2020 2:24 pm
Forum: Troubleshooting
Topic: Dead after 5.5V Input at micro USB
Replies: 45
Views: 1343

Re: Dead after 5.5V Input at micro USB

Strange things come to the point that in the last Raspberries there is no protection at all, even the most primitive, which is put in the cheapest devices (zener diode and fuse). This is not correct. The Pi4B has a TVS diode for reverse polarity and overvoltage protection (see the schematic ). It d...
by davidcoton
Sat Feb 22, 2020 10:49 am
Forum: Off topic discussion
Topic: My kid is using a Raspberry Pi - should I call the police???
Replies: 33
Views: 1881

Re: My kid is using a Raspberry Pi - should I call the police???

hippy wrote:
Sat Feb 22, 2020 9:11 am
I have no desire to participate in a game of 'moving goalposts'.
Whose kids moved the goalposts? Was a Raspberry Pi involved? :lol:
by davidcoton
Thu Feb 20, 2020 6:31 pm
Forum: General discussion
Topic: Came with my Pi 4 kit
Replies: 4
Views: 185

Re: Came with my Pi 4 kit

gordon77 wrote:
Thu Feb 20, 2020 6:24 pm
"slightly dodgy to back up the running OS, though"

Not dodgy if you use the raspbian SD card copier ?
I would hope not, but does the SDCard Copier guarantee not to read things as they change? I have always thought this problem was fairly fundamental.
by davidcoton
Thu Feb 20, 2020 6:18 pm
Forum: General discussion
Topic: Came with my Pi 4 kit
Replies: 4
Views: 185

Re: Came with my Pi 4 kit

Looks like a USB to SDCard adapter. It can be used on your PC for writing downloaded OSs to the SDCard, or for backing up the SDCard in the Pi (slightly dodgy to back up the running OS, though).
by davidcoton
Wed Feb 19, 2020 10:39 pm
Forum: Troubleshooting
Topic: RPI 4 Boot up and USB
Replies: 4
Views: 191

Re: RPI 4 Boot up and USB

I notice from the listing that the PSU has a switch on the 5V side. This feature is known to be a common source of problems. Is there a lightning flash on the top right of the screen? Does the Pi's red PoWeR LED ever go out? If either of these happen, it's a supply problem. The official RPT PSU is g...
by davidcoton
Wed Feb 19, 2020 10:20 am
Forum: General discussion
Topic: How to demonstrate high speed broadband in an imaginative way?
Replies: 2
Views: 167

Re: How to demonstrate high speed broadband in an imaginative way?

Will others in the village have access to the new system by the open day? If so, set up four Pis with cameras in public places around the village, each streaming HD video. Display the four streams simultaneously on the big screen. Have another camera at the school, so that the links are all two-way....
by davidcoton
Tue Feb 18, 2020 10:20 pm
Forum: Advanced users
Topic: Raspberry Pi Zero W + External Antenna (Certified)
Replies: 3
Views: 177

Re: Raspberry Pi Zero W + External Antenna (Certified)

you could use a usb wifi device but it would be of absolutely no benefit aside from the ability to reposition it as the Pi already uses the maximum power permissible. It can be a major benefit, because the physically small antenna on the Pi is not very efficient, and a USB adapter with a well-desig...
by davidcoton
Tue Feb 18, 2020 10:15 pm
Forum: General discussion
Topic: Powering Pi Zero with AA batteries
Replies: 25
Views: 772

Re: Powering Pi Zero with AA batteries

Heater wrote:
Tue Feb 18, 2020 9:57 pm
4 Watts for half an our is only 2 Watt/hours.
Now who's confusing units?
The common (non-SI) unit of energy used for battery capacity is the Watt-hour (Wh), power multiplied by time.
A joule is the SI unit of energy, 1 Watt second.
1 Wh = 3600J
by davidcoton
Tue Feb 18, 2020 10:04 pm
Forum: Troubleshooting
Topic: RPI 4 Boot up and USB
Replies: 4
Views: 191

Re: RPI 4 Boot up and USB

What are you using for a power supply?
by davidcoton
Tue Feb 18, 2020 10:02 pm
Forum: Troubleshooting
Topic: switch monitor
Replies: 2
Views: 267

Re: switch monitor

miguelcanal88 wrote:
Tue Feb 18, 2020 8:20 pm
I'm having the same problem now. Did you find any solution to this?
You are unlikely to get an answer. superkind has not logged on for three years.
by davidcoton
Tue Feb 18, 2020 9:55 pm
Forum: Troubleshooting
Topic: Raspberry Pi green LED
Replies: 5
Views: 100

Re: Raspberry Pi green LED

Just to avoid a possible problem that others have found, you are using the SDCard slot on the board, not on a plug-in USB card reader?
by davidcoton
Tue Feb 18, 2020 9:52 pm
Forum: Troubleshooting
Topic: Dead after 5.5V Input at micro USB
Replies: 45
Views: 1343

Re: Dead after 5.5V Input at micro USB

Read my previous answer again, and rpdom's post. Try to understand what is written, not what you think it says. Bypassing the polyfuse is not a good idea. With no power supply, you can measure the resistance of the polyfuse. It should be low (virtual short circuit). If not, give it time to recover a...
by davidcoton
Tue Feb 18, 2020 9:31 pm
Forum: Beginners
Topic: Consumption raspberry pi zero w
Replies: 9
Views: 214

Re: Consumption raspberry pi zero w

ejolson wrote:
Tue Feb 18, 2020 5:29 pm
How many errors are in that chart?
Discussed in another thread.
by davidcoton
Tue Feb 18, 2020 9:24 pm
Forum: General discussion
Topic: Pi4 broken after about 1 hour of use?
Replies: 4
Views: 336

Re: Pi4 broken after about 1 hour of use?

Imperf3kt wrote:
Tue Feb 18, 2020 9:07 pm
sounds like some form of short circuit.
I'd run a continuity check between 5v and ground, see if there's current flowing somewhere.
Tells you absolutely nothing -- current is supposed to flow from 5V to ground. The question is, how much, and where? A continuity check is not appropriate.
by davidcoton
Tue Feb 18, 2020 3:01 pm
Forum: Off topic discussion
Topic: My kid is using a Raspberry Pi - should I call the police???
Replies: 33
Views: 1881

Re: My kid is using a Raspberry Pi - should I call the police???

They certainly don't need cake and Pi. :lol:
It sounds as though ROCU could use CAKE, though.

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