Heads up if you are installing the keyswitch power option

[Carl Claunch]

The Hacks page lists an option to install a power keyswitch and USB-C receptacle in the holes that are already provided on the back panel. I installed the connectors onto the LED PCB and wired it up, using the recommended 12mm keyswitch and USB-C power receptacle.

When I plugged the Raspberry Pi 27W power supply into the receptacle, nothing happened. 

In hindsight that makes perfect sense. The power supply for the Pi 5 can support multiple voltages and currents up to its 27W limit - the only way it can determine what voltage to feed is to negotiate with the Pi to agree on the profile to use. 

The USB receptacle provides just two wires, has no way to negotiate and therefore the Pi supply will not deliver any power to it. 

To use this power option, you can't use the RPi 5 power supply. I will need to buy a less smart power supply that delivers a fixed 5V on USB-C with no need for a protocol negotiation. Plan for this if you are going to implement this hack. 

[johntk...@gmail.com]

Maybe wire the key switch to the Pi 5’s onboard power switch jumper instead?

The J2 jumper is located between the RTC battery connector and the board edge. This breakout allows you to add your own power button to Raspberry Pi 5 by adding a Normally Open (NO) momentary switch bridging the two pads. Briefly closing this switch will perform the same actions as the onboard power button.

[Brian welland]

Hi,

Have you actually pressed the onboard Pi 5 on/off push-button after you used the keyswitch? 

All my Pi 5 units only work after I use the on/off switch following plugging in the official Raspberry Pi 27W supply.

Trust this helps.

 

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[Carl Claunch]

Hi Brian

On my RPi 5, when I have the 27W supply plugged directly into the Pi and plug the supply in, it starts up immediately. I have never had to use the power button. Maybe this is some Pi configuration option?

I did try plugging it into the receptacle for the keyswitch, turning on the switch and pushing the button on the Pi, but no effect at all.

Since the supply can provide multiple voltages, I don't see how it can know which to use when the receptacle is just two wires. 

Carl

[Haritech (Gmail)]

The supply will always default to 5v if it can’t negotiate. 

Lawrence

On Jul 18, 2024, at 07:04, Carl Claunch <carlcl...@gmail.com> wrote:

Hi Brian

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[Carl Claunch]

When I hook up the supply to any of the two wire receptacles, I see 0V across the leads, with or without an electronic load. 

[oscarv]

Carl,

I don't think this will be your problem, but just in case: you did connect the power switch (blue/red trace leading in to it)? See the circuit layout - if the switch is not set, the voltage does not make it to the Pi:

But from your description, that is not the issue. I tested with a Pi 4 power supply (which works fine for my Pi 5 without any power-hungry accessories). 

Should I try with a Pi 5 'smart' power supply too? Indeed, that one is supposed to just default to output 5V. Let me know if you indeed have the problem persisting, and I will!

Kind regards,

Oscar.

[Carl Claunch]

Hi Oscar

I did wire it that way and confirmed connectivity via ohmmeter as well.

When I use a spare two wire USB-C socket and plug in the supply, I see 0V coming from the supply. Thinking it might need a load, a la PC power supplies, I hooked it to an electronic load set to a couple hundred ma but still zero volts. Clearly this is a behavior of the particular Pi 5 27W supply I bought. 

In any case, I instead converted the keyswitch to a momentary pushbutton and wired that to the J2 on the Pi 5, as suggested by another member of the forum. That sends a signal that causes the Pi to execute an orderly Debian shutdown, which is preferable to maintain the integrity of the filesystems. Doesn't look as authentic but enhanced behavior considering the hidden Linux in the Pi. 

Carl

[terry-...@glaver.org]

USB-C continues the "2 steps forward, 3 steps back" of USB history.

A USB-C supply (a box with a wall plug on one end and a USB-C socket on the other) defaults to providing no power. This is because all USB-C to USB-C cables are supposed to be male at both ends, and you can imagine the hilarity that would ensue when two 60W+ supplies both tried to power the same cable.

In order for a USB-C supply to provide power, it either needs to see "programming resistors" on its CC1 and CC2 pins that tell it what sort of thing it is connected to*, or an intelligent IC that can negotiate for higher power, current, or both.

* There have been various unintentional and intentional foulups along the way. The first production rev of the Raspberry Pi 4 said "I'm a pair of passive headphones, don't worry about giving me any power". Certain brands of smartphones/tablets ship with chargers that default to wildly inappropriate voltage and/or current output (one such supply provides over 20V). In theory, to comply with the USB Implementers Forum requirements, devices that specify their desire via programming resistors are limited to the "classic" 500mA at 5V. Raspberry Pi (or other large resellers like Canakit) provide supplies that can provide far more than 500mA (which won't get you far on a modern Pi), but which apparently do not utilize the CC pins. All of these Pi-specific chargers that I've seen have had USB-C cables permanently attached to the wall plug part.

A USB-A charger with a USB-A to USB-C cable doesn't know anything about any of this, and just supplies 5V, presumably at the 500mA standard.

In summary: A USB-C charger and a USB-C to USB-C cable won't work with the snap-in 2-wire socket option on the back of the case. A Raspberry Pi (or other large reseller) charger will probably power it, but the leads I've seen on those snap-in sockets don't inspire confidence that they are sufficient for the current. A USB-A to USB-C cable into that socket may provide enough current to start the PI, but probably not.

Users are much better off using a Raspberry PI (or other major brand) Pi supply plugged directly into the USB C port on the back of the PI. After all, it is sticking out of the back of the case on the PiDP-10 (unlike on the -11).