The new Zynthian case is wonderful but the project is slightly disadvantaged by the poor power input method for the Raspberry Pi. In my view, micro USB connectors are not reliable enough for long-term use and are prone to slipping out. I know that many music hardware manufacturers are now using this connection type to save space, but if it can be avoided or improved upon, then this should be a goal. I have 4 possible suggestions for discussion:-
add a cable clamp next to the power input connector to hold the USB cable in place
Semi-permanently attach a USB cable to the case with a blob of silicon rubber
Move the Pi + HiFiBerry away from the back wall of the case and add a more robust barrel connector to the case with an internal USB cable connecting from the PI to the barrel connector
Options 1 and 2 are quick and dirty solutions. People that really need to improve the power input right now can implement one of this 2 methods quite easily.
Option 3 has more “contras” than “pros”, IMHO.
Option 4 is the more elegant, and could have some interresting side benefits, like:
add a poweron/poweroff mechanism
include a small LIPO battery and a charging circuit
I’m not sure what the best solution is, but I agree that the micro USB connector is a poor choice for powering Zynthian. I’ve managed to break off the micro USB from a couple of RPi boards in the past & it’s impossible to solder them back on again.
A dream solution would be to have a USB B ("Printer connector) on the back of Zynthian. Then we can use a thicker USB A-B cable connect to a 5V PSU. These cables have much bigger cores so the voltage drops are much less than with the spindly micro USB cables.
I had lots of problems during booting until I used a better USB charger (2.4 A rated) and a real USB charger cable (2 A rated).
my disco-Zynthian ahs a 5A power supply - but currently with a micro-SD adapter. Will fix this as soon as I have time (and have a free Raspi3 for exchanhing the current Raspi2).
I used the same cable, cut it, shortened it and added a switch…
And by the way, RPi3, Hifiberry DAC+, midi keyboard, ttl midi out, extra leds, touchscreen etc… and never more than 0.6A current draw, even under heavy load.
I would recommend not using any type of USB connector to power the device if you want to move it around, e.g. take to gigs. Even the USB Type B is prone to failure. It is easily dislodged and I have a QX49 that has a faulty socket. (The central plastic locator can become unconnected and push back within the socket.) I would recommend using a standard (as if there is such a thing!) power connector proven in use over many years, e.g. concentric connectors used by Roland et al. (Better still - a locking connector.) Then have an internal power regulator (which could integrate with a rechargeable battery like jofemondo suggested which provides portability plus UPS). (I don’t personally like these connectors but they are still working on my 40 year old musical devices!!!) Or go a stage further and add an internal power supplier with IEC 60320 power inlet to get rid of the wall-wart all together. The further we get away from the micro USB the better (but probably also more complex and expensive).
Regarding power switch - adding a simple, press to make switch between pins 5 & 6 allows a powered but shutdown RPi to be booted. I have this on my Zynth and it works well. Because you don’t generally press it during normal operation it does not interfere with the I2C clock. (I2C recovers fine if you do press the button - it just won’t work whilst the button is pressed.) I haven’t bothered with implementing power off for this button because we have the option to long press the Select knob. I would recommend adding this power-on button to the core design.
