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by TerryC65
Thu Sep 17, 2020 1:40 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: The Nature of SPI Bus Support on the Pi
Replies: 14
Views: 836

Re: The Nature of SPI Bus Support on the Pi

I can now report that the SPI Page at https://www.raspberrypi.org/documentati ... /README.md has now been updated to reflect the correct hardware arrangements.

Many thanks to all who contributed to this change.
by TerryC65
Mon Sep 14, 2020 1:45 pm
Forum: Networking and servers
Topic: Enabling SSH on one of two Ethernet Ports
Replies: 2
Views: 108

Re: Enabling SSH on one of two Ethernet Ports

Thanks for this. Setting the ListenAddress should be fine since the Pi has been set up with fixed IP Addresses which are unlikely to change before the world moves over to IPv6 :D
by TerryC65
Mon Sep 14, 2020 1:06 pm
Forum: Networking and servers
Topic: Enabling SSH on one of two Ethernet Ports
Replies: 2
Views: 108

Enabling SSH on one of two Ethernet Ports

I have a Raspberry Pi which is acting (amongst other things) as a router between two subnets, so it has two ports, the default eth0 and eth1 via a USB / Ethernet Adaptor. I enabled SSH but cannot see how to disable it only on eth1. I realise that I can block SSH using the firewall, but is there a mo...
by TerryC65
Sun Aug 30, 2020 2:00 pm
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

The problem with that is, the only way I can see of determining what the maximum is, is by risking destructive testing. Which is a very unreliable way to establish capability. When the tests are complete, how can anyone be sure that the sample chosen wasn't a particularly 'good' one? Test another o...
by TerryC65
Sun Aug 30, 2020 1:45 pm
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

The capability of the PAM2306AYPKE in this case (or of the switcher IC in the general dc-dc converter cse) is not the only factor. Saturation current of the inductor or ripple current in capacitors could impose a lower limit. Even more reason not to rely on the available current if the total consum...
by TerryC65
Sun Aug 30, 2020 6:58 am
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

Thanks for all the suggestions. I must say that there seems to be a wide disparity between the figures quoted; 50 mA to 800 mA :!: :lol: As I said at the beginning, when I raised this query I had already looked at the low level specs including the schematics for the Pi Zero. From the schematic I fou...
by TerryC65
Sat Aug 29, 2020 8:52 pm
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

FTrevorGowen wrote:
Sat Aug 29, 2020 8:40 pm
FWIW, I've used a MCP1700 for a backlit 3.3V display but it's a 250mA device which may not be enough for your purposes.
That might just be enough. If nothing else I could use two; one for a pair of displays.

Thanks for the tip.
by TerryC65
Sat Aug 29, 2020 7:58 pm
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

If you are worried about a clean 3.3v and are already using a buck converter for the 12-5v transition the best solution is probably a linear 3.3v regulator from the 5v rail. This will be 66% efficient and only dissipate under .5w at 200ma. I've been trying to find a linear converter that will work ...
by TerryC65
Sat Aug 29, 2020 4:24 pm
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

If you really think you won't need more than 200mA from that external regulator I would go to some length to satisfy myself that the Zero's onboard 3.3 volt supply is not up to the task. I may do that before committing to a separate regulator. It depends on what comes out of my current consumption ...
by TerryC65
Sat Aug 29, 2020 4:02 pm
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

That is a linear regulator. It does the conversion by converting electricity into heat. More than 4 Watts of heat if you want to take the full 500mA. Yes we know, it is also a lot quieter than an equivalent Buck Converter and will take up less real estate (which we are beginning to get short of). H...
by TerryC65
Sat Aug 29, 2020 3:24 pm
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

This. https://elinux.org/RPi_Low-level_peripherals#Power_pins Says 50mA This https://raspberrypi.stackexchange.com/questions/51615/raspberry-pi-power-limitations Says someone got 800mA. And that's the problem. In the absence of a spec people try to come up with something themselves and end up with ...
by TerryC65
Sat Aug 29, 2020 11:54 am
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

Subtracting that calculated current from the capability of the 3.3 volt dc-dc converter gives what should be safe to take for off-board use. But be aware that it is not only the dc-dc converter IC that determines the capability - the inductor does too. I fear that it is more complicated than that, ...
by TerryC65
Sat Aug 29, 2020 10:11 am
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

It's not actually recommended to power things from the 3.3V pins other than very low current devices. This is because a surge on that pin when things are switched on can upset the voltage regulator and cause instability with the Pi (I think this mostly applies to the later models.). We are aware of...
by TerryC65
Sat Aug 29, 2020 10:07 am
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

Closest I can find is https://www.raspberrypi.org/forums/viewtopic.php?t=208705 You did a better job than I did at searching the Forums; I tried but never found that. :? That link suggests that the internal regulator is good for 1 A whereas the spec of the device used in the Pi Zero says 1.5 A. See...
by TerryC65
Sat Aug 29, 2020 9:40 am
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

Do you mean the gpio pins or the 2 3.3v supply pins ? Dougie has answered for gpio but the 3.3v is a bit more vague, l think it used to be 50mA but then the 3.3v regulator was uprated in later pi's. 3.3 V Pins. pinout.xyz says 500 mA (if you follow the link), but I'd like to see an actual spec if t...
by TerryC65
Sat Aug 29, 2020 9:36 am
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Re: Maximum Current Output from 3.3 V Pins - Pi Zero

DougieLawson wrote:
Sat Aug 29, 2020 9:34 am
It's 16mA per pin (which is just enough to switch a transistor and nothing more).
Max 50ma for each 8 GPIO bank.
Isn't that the GPIO Pins? My question was about the two 3.3 V pins - 1 and 17.
by TerryC65
Sat Aug 29, 2020 8:48 am
Forum: Advanced users
Topic: Maximum Current Output from 3.3 V Pins - Pi Zero
Replies: 33
Views: 1077

Maximum Current Output from 3.3 V Pins - Pi Zero

Hi, Can anyone point me to the specification for the output current capacity for the Pi Zero 3.3 V Pins? I've had a look at the hardware Spec at https://www.raspberrypi.org/documentation/hardware/raspberrypi/README.md , but can only find the input current draw for the various models, but nothing abo...
by TerryC65
Tue Aug 18, 2020 3:18 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: The Nature of SPI Bus Support on the Pi
Replies: 14
Views: 836

Re: The Nature of SPI Bus Support on the Pi

Write an update for the docs at: https://github.com/raspberrypi/documentation/blob/master/hardware/raspberrypi/spi/README.md then create a Github pull request. Unfortunately Dougie, as I said above; 'I would be happy to do this, but I hesitate to do so because of my limitations in understanding wha...
by TerryC65
Tue Aug 18, 2020 9:04 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: The Nature of SPI Bus Support on the Pi
Replies: 14
Views: 836

Re: The Nature of SPI Bus Support on the Pi

Thanks to all for the feedback; I've learnt a lot. Although I hesitate to criticise, I believe that there are significant discrepancies between the various resources available on this subject. As I mentioned at the outset the Raspberry PI SPI Documentation ( https://www.raspberrypi.org/documentation...
by TerryC65
Mon Aug 17, 2020 3:09 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: The Nature of SPI Bus Support on the Pi
Replies: 14
Views: 836

Re: The Nature of SPI Bus Support on the Pi

The additional SPI controllers only exist on the Pi 4 and most of them can be mapped to the GPIO header. I just had another look at /boot/overlays/README on one of our Pis and this is what it says about SPI2: Name: spi2-1cs Info: Enables spi2 with a single chip select (CS) line and associated spide...
by TerryC65
Mon Aug 17, 2020 12:58 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: The Nature of SPI Bus Support on the Pi
Replies: 14
Views: 836

Re: The Nature of SPI Bus Support on the Pi

FYI I've raised an issue about this on the Pinout.xyz GitHub page (https://github.com/Gadgetoid/Pinout.xyz/issues/372). The problem, as noted, isn't that Pinout.xyz is wrong; it is simply that it's misleading.

Thanks for explaining the situation to me Dougie.
by TerryC65
Mon Aug 17, 2020 12:41 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: The Nature of SPI Bus Support on the Pi
Replies: 14
Views: 836

Re: The Nature of SPI Bus Support on the Pi

That is interesting. If I've understood the information in /boot/overlays/README correctly, the SoC has hardware support of up to 6 discrete SPI Busses (but only 2 for 'normal' RPis (eg not Compute Modules)). That's quite impressive!
by TerryC65
Mon Aug 17, 2020 12:01 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: The Nature of SPI Bus Support on the Pi
Replies: 14
Views: 836

Re: The Nature of SPI Bus Support on the Pi

I'm not sure why https://pinout.xyz/pinout/spi includes the normally inactive SPI1 stuff. Ah! So the second bus exists, but isn't normally available. There's more than one way to wire multiple devices. They can either get a chip select each. Of for devices that pass the bus from input to output you...
by TerryC65
Mon Aug 17, 2020 11:33 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: The Nature of SPI Bus Support on the Pi
Replies: 14
Views: 836

The Nature of SPI Bus Support on the Pi

I must confess to being a bit confused about how the Pi supports the SPI Bus. Wikipedia gives a fairly clear description of how SPI Bus works and this section of its page on the Topic shows how multiple devices may be connected to a generic SPI master https://en.wikipedia.org/w/index.php?title=Seria...
by TerryC65
Tue Jul 07, 2020 2:10 pm
Forum: Networking and servers
Topic: DNS Server Not Resolving
Replies: 4
Views: 233

Re: DNS Server Not Resolving

I've fixed this. Like most of these things there was a combination of things, but the main problem was that I had put the entry in the hosts file using the device's hostname against the IP address instead of the Web Address.

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