This is a conversation with my imaginary second half, I call her Jane. We’ve been talking about a better USB power concept that would free up a second USB port on the CHIP and protect the PC/Laptop.
Jane: Hey, have heard about the cool new “no-limit” version of CHIP-OS
Jane: You don’t sound amazed, it solves all the power problems, what’s the matter?
Me: Well we’ve talked about the AXP (the power controller of CHIP) and how it handles the three power sources, right?
Jane: Yes, there is the (1) micro-USB-in which can be current limited to 500/750mA and no-limit (2) AC-IN / CHR-IN (the first two pins on the left header, 2.3A in max) and (3) the battery connector
Me: Correct. Now the USB (1) has a dual purpose, as you know. We’ve used it for power and for communication via ‘sudo screen /dev/ttyACM0 115200’ to the CHIP. That’s a very neat feature as you can just walk around with CHIP and our laptop, plug in one cable and you’re good to go. It was a safe way because the current limiting feature of the AXP avoided that we’d burn our Laptop USB port.
Jane: Uhhh, I think I get it… That feature has just been disabled. So is our Laptop at risk?
Me: Well, in 90% of the cases, it’s not! Modern laptop can provide more than the 500/750mA and will provide their own overcurrent fuse. But if you tinker around with the CHIP and you short something, or add/remove DIPs which might require a current spike to reload their onboard capacitance – in those cases you could destroy your laptops USB ports, yes.
Jane: Was that the reason why NTC limited the current in the first place?
Jane: So what shall I do?
Me: As long as you just have the CHIP connected to your PC everything is alright. Make sure that you don’t drop liquids on it, or metal object like a paperclip, as this might destroy not only your CHIP but also your Laptop. Another solution would be an external power supply, e.g. the QUEOS and the SALSA carry those. They will provide rock-solid 5V to the CHIP via CHR-IN from any given external voltage (7-28V).
Jane: Yea, ok… but not everyone needs a USB hub and it’s kind of pricy compared to the CHIP.
Me: True, so another solution would be to connect your no-limit-CHIP only to a USB wall charger not to a PC. Even if CHIP goes crazy and surge too much current – worst thing is a broken wall charger.
Jane: OK, that’s a good suggestion. A wall charger, but when I use the micro USB with a wall charger, how will I communicate then? I can’t connect two cables to the same micro-usb-jack.
Me: True, but you still have ssh via Wi-Fi, or you could use a USB to Serial cable and hook it up to the header, or … never mind
Me: Well, in an idea world NTC would have installed a dedicated micro-usb-power-jack that is connected to the CHR-IN (2) like the QUESO is. Power only on that extra-jack and leave the overcurrent protection of the original jack at 750mA.
Jane: Ah, I see. One extra jack for power coming from a wall charger that can deliver as much current as needed (up to 2.3A) and the original micro USB for communication. Or really as a second USB port? I’ve read the micro USB supports USB-on-the-go! So that would give me a second USB port, right?
Me: Correct, you’d have two-ish USB ports for your peripherals and there is no danger, even if you hook CHIP up to your PC due to the protection feature. Heck, you can also still TRY to power your CHIP via your laptop – worst thing that can happen is a brown out on the CHIP.
Jane: Sounds better than a burned USB jack on a laptop. So why is there no dedicated mico-usb- power -jack?
Me: I really don’t know. It has been suggested many times in the forum but it is still missing. People asked for this connector on the DIP, but it’s simply not there. I guess cost could be a reason. But Jane, we could build our own boards with micro-usb- power-jacks if you want to. VGA, HDMI, ETHERNET, USB-HUB-light ..