HawaiianPi wrote: ↑
Sat Oct 12, 2019 10:53 pm
alphanumeric wrote: ↑
Sat Oct 12, 2019 6:14 pm
One thing I have noticed with a Zero is if its booted up, and you swap or plug something into the USB DATA port it has a habit of rebooting.
That seems to be a problem with the newer models. There must have been some hardware change that was not accompanied by a revision change (same v1.1 revision number as 2016 model), but they do have a newer date on them (2017), and those are the ones with the rebooting issue when hot swapping USB devices (from what I've been reading in threads here).
Rebooting when plugging some USB device in, while the PI is already running, is normal
with a RPI Zero, the same thing happened with the original RPI 1.
When you "hot plug" an USB device in, on a zero, the zero's boards power collapses, because you suddenly connect a large(-ish) discharged capacitor, (on the 5V rail of the USB device you plug in) in parallel to the similar sized capacitance on the Zero. The zero sees this as a "short" of the 5V line (for a very short time, but long enough to crash a computer).
Charges on both capacitors equal out, and the largest capacitor "wins".
For example with equal capacitances the voltage over both is suddenly reduced to half
the original voltage, or 2.5V, which means the PI crashes.
Its called the "inrush current" problem, and later PI's all had some mechanism to reduce the inrush current so USB devices became "hot pluggable".
The are two solutions:
1) don't hot plug in USB devices.
2) do something to mitigate the voltage drop caused by hot plugging.
The second solution in practical terms, as limiting the current isn't really possible without putting a limiting device in between 5V and the USB device, would be to add a low impedance large capacitor over the 5V rail close to the USB connector. With large meaning something like 1000uF.
so that is why its not mounted on the zero already, because it would be physically large as well.
Another solution would be to use an USB hub, these generally have rush in current limitation solutions in place.