Raspberry Pi Forums

davidcoton

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...

davidcoton

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.

davidcoton

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

davidcoton

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.

davidcoton

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...

davidcoton

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.

davidcoton

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...

davidcoton

I don't know the range, but the usage precludes 5GHz as that is not licenced for outdoor use (IIRC).

davidcoton

Depends entirely on what you want to achieve with them. Give us more info to work with.

davidcoton

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...

davidcoton

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?

davidcoton

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.

davidcoton

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).

davidcoton

See this post.

davidcoton

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...

davidcoton

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....

davidcoton

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...

davidcoton

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

davidcoton

What are you using for a power supply?

davidcoton

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.

davidcoton

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?

davidcoton

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...

davidcoton

ejolson wrote: ↑
Tue Feb 18, 2020 5:29 pm
How many errors are in that chart?

Discussed in another thread.

davidcoton

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.

davidcoton

They certainly don't need cake and Pi.

It sounds as though ROCU could use CAKE, though.

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