ejolson
Posts: 6044
Joined: Tue Mar 18, 2014 11:47 am

Re: Why USB-C ?

Sat Mar 14, 2020 3:36 pm

bensimmo wrote:
Sat Mar 14, 2020 2:55 pm
I have no idea, why one wouldn't use and extension lead before the PSU.

I'm just commenting that they would alter the voltage into the longer inline switched wire to compensate for the extra voltage drop. Maybe using a thicker gauge.so it would give 5.1V and a capability of delivering up to 3A at the usb-C end.

'they' being the manufacturers of the PSU.
Increasing the voltage much beyond 5V to compensate for resistance in the switch and wire is difficult, because of how variable is the amount of current used by the Pi. In particular, the Pi draws between 0.68 and 3 amps which implies it provides a load between 1.67 and 7.35 ohms.

Question 1. If the voltage of the source supply is stable, what is the maximum resistance of the delivery wire such that the voltage at the Pi end varies no more than plus or minus 10% over the range from minimum to maximum loads.

Question 2. Consider the design of a DC power supply with a feedback control that increases the output voltage linearly as current is increased. Calibrate this control as well as possible to provide a stable 5V potential at the end of a delivery wire that has an internal resistance of 1 ohm. Comment on the practicality of this design.

Question 3. Repeat question 2 but for the case when the wire provides 2 ohms of resistance. What happens if a 0.5 ohm wire is substituted without recalibrating the control in the power supply? Explain.

alphanumeric
Posts: 2675
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Location: Sydney, Nova Scotia, Canada

Re: Why USB-C ?

Sat Mar 14, 2020 6:52 pm

This is IMHO one of those, you can't please all of the people all of the time, type deals. What works for one person doesn't cut it for somebody else. And just about any solution will have pluses and minuses. I do like the move to USB C over Micro USB. No worries of trying to plug it in upside down and breaking something.

W. H. Heydt
Posts: 13644
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Why USB-C ?

Sat Mar 14, 2020 7:55 pm

alphanumeric wrote:
Sat Mar 14, 2020 6:52 pm
This is IMHO one of those, you can't please all of the people all of the time, type deals. What works for one person doesn't cut it for somebody else. And just about any solution will have pluses and minuses. I do like the move to USB C over Micro USB. No worries of trying to plug it in upside down and breaking something.
Agreed, on both points. On the whole, probably beneficial in the long run.

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bensimmo
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Location: East Yorkshire

Re: Why USB-C ?

Sat Mar 14, 2020 8:06 pm

ejolson wrote:
Sat Mar 14, 2020 3:36 pm
bensimmo wrote:
Sat Mar 14, 2020 2:55 pm
I have no idea, why one wouldn't use and extension lead before the PSU.

I'm just commenting that they would alter the voltage into the longer inline switched wire to compensate for the extra voltage drop. Maybe using a thicker gauge.so it would give 5.1V and a capability of delivering up to 3A at the usb-C end.

'they' being the manufacturers of the PSU.
Increasing the voltage much beyond 5V to compensate for resistance in the switch and wire is difficult, because of how variable is the amount of current used by the Pi. In particular, the Pi draws between 0.68 and 3 amps which implies it provides a load between 1.67 and 7.35 ohms.

Question 1. If the voltage of the source supply is stable, what is the maximum resistance of the delivery wire such that the voltage at the Pi end varies no more than plus or minus 10% over the range from minimum to maximum loads.

Question 2. Consider the design of a DC power supply with a feedback control that increases the output voltage linearly as current is increased. Calibrate this control as well as possible to provide a stable 5V potential at the end of a delivery wire that has an internal resistance of 1 ohm. Comment on the practicality of this design.

Question 3. Repeat question 2 but for the case when the wire provides 2 ohms of resistance. What happens if a 0.5 ohm wire is substituted without recalibrating the control in the power supply? Explain.
I'm sure Strontronics, XP Power etc are more than capable of working it out how to get 5.1V u see normal use at the uUSB/USBc end and keep it in spec at a 3A draw.

I don't need a switch in mine, but you can buy them.
Not something the RPF need to worry about in my opinion, I don't see the expense as a need for the majority of people.
And the Pi4 will run off 2.5A happily, hence the adaptor for the older PSUs, there just isn't as much USB headroom.
So uUSB supplies can still be used https://www.raspberrypi.org/products/us ... c-adapter/


For me USB-C is great as I don't have to turn the cable over to fit it. And now my phone's and laptops and Switch are all using it.
If it was a barrel, I may well have stick a 12V,4.5V, 9V, 15.5V or whatever other one I have in.

USB keeps is safe!
I assume most agree on that.

pica200
Posts: 219
Joined: Tue Aug 06, 2019 10:27 am

Re: Why USB-C ?

Sat Mar 14, 2020 8:19 pm

Yeah, it's good the voltage levels are standardized and USB always starts at 5V unless power supply and device agree on something else. Being able to plug USB-C plugs in either way is more of a convenience feature but i can understand why people like it.

Heater
Posts: 16874
Joined: Tue Jul 17, 2012 3:02 pm

Re: Why USB-C ?

Sat Mar 14, 2020 8:57 pm

On a slightly sideways note. I sometimes wonder why we bother having standards.

Despite standards it seems every time I get a new toy I need yet another bunch of adapters to play with it.

And soon enough my existing cables and adapters become useless.

The Pi 4 required I get micro-HDMI and USB C.

That is the latest in the line after I have accumulated a hug box full of cables and adapters dating back to Centronics parallel port printer cables and RS-232 null modems.

Meanwhile my recent MS Surface Pro 4 has a display port socket and my only spare monitor has something that look a bit like HDMI but is not.

Not to mention all the wall warts I have with barrel connectors. And historic USB cables.

It's hopeless. Just got to keep buying more cables and adapters every year. They will end up languishing in my junk box next year. Grrr...
Memory in C++ is a leaky abstraction .

ejolson
Posts: 6044
Joined: Tue Mar 18, 2014 11:47 am

Re: Why USB-C ?

Sat Mar 14, 2020 10:22 pm

bensimmo wrote:
Sat Mar 14, 2020 8:06 pm
ejolson wrote:
Sat Mar 14, 2020 3:36 pm
bensimmo wrote:
Sat Mar 14, 2020 2:55 pm
I have no idea, why one wouldn't use and extension lead before the PSU.

I'm just commenting that they would alter the voltage into the longer inline switched wire to compensate for the extra voltage drop. Maybe using a thicker gauge.so it would give 5.1V and a capability of delivering up to 3A at the usb-C end.

'they' being the manufacturers of the PSU.
Increasing the voltage much beyond 5V to compensate for resistance in the switch and wire is difficult, because of how variable is the amount of current used by the Pi. In particular, the Pi draws between 0.68 and 3 amps which implies it provides a load between 1.67 and 7.35 ohms.

Question 1. If the voltage of the source supply is stable, what is the maximum resistance of the delivery wire such that the voltage at the Pi end varies no more than plus or minus 10% over the range from minimum to maximum loads.

Question 2. Consider the design of a DC power supply with a feedback control that increases the output voltage linearly as current is increased. Calibrate this control as well as possible to provide a stable 5V potential at the end of a delivery wire that has an internal resistance of 1 ohm. Comment on the practicality of this design.

Question 3. Repeat question 2 but for the case when the wire provides 2 ohms of resistance. What happens if a 0.5 ohm wire is substituted without recalibrating the control in the power supply? Explain.
I'm sure Strontronics, XP Power etc are more than capable of working it out how to get 5.1V u see normal use at the uUSB/USBc end and keep it in spec at a 3A draw.
You seem to have misunderstood the educational opportunity to work it out for yourself. Although brands are people too, some real person must have done the engineering for the Strontronics and XP Power companies to have any products to sell at all.
Last edited by ejolson on Sat Mar 14, 2020 10:34 pm, edited 1 time in total.

W. H. Heydt
Posts: 13644
Joined: Fri Mar 09, 2012 7:36 pm
Location: Vallejo, CA (US)

Re: Why USB-C ?

Sat Mar 14, 2020 10:27 pm

ejolson wrote:
Sat Mar 14, 2020 10:22 pm
Although brands are people too, some person must have done the engineering for the Strontronics and XP Power companies to have any products to sell at all.
It's a peculiarity of US jurisprudence, but I think it applies here: I'll believe corporations are people when Texas executes one.

alphanumeric
Posts: 2675
Joined: Tue Jan 19, 2016 2:17 pm
Location: Sydney, Nova Scotia, Canada

Re: Why USB-C ?

Sat Mar 14, 2020 10:47 pm

For me personally, I still have a couple of Pi A+'s, some 3B and 3B+'s, and the newer 3A+ and 4B. And some Zero and Zero W's kicking around. My older cables and power supplies are still seeing some useful use and regularly come in handy. I have 2 dozen or so Pi's kicking around here. About 1/3 see daily use. The others get used here and there for test setups and just trying things out.
Power supply wise its mostly the two official ones in use, 2.5A Micro USB and the new 3A USB C.
HDMI wise I have at least three cables on the go. HDMI to HDMI, Mini HDMI to HDMI, and Micro HDMI to HDMI.
And a couple of USB Hubs for the A+, 3A+, and Zero's.
Changing standards is nothing new though, in the PC world and otherwise. Thats just the way it goes if you want to be cutting edge. ;)

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