So, I have a Raspberry PI B+. It has HDMI video output. Since the only device in my house that has HDMI input is the TV, which is in another room and is usually occupied by my wife, and as my monitor has a spare DVI input, I bought a HDMI -> DVI converter. The strange thing is, it works only when I power the Pi from a PC.
- The Pi, when plugged in to the TV (via normal HDML cable) works, when powered by a 3A USP power supply (haven't tried others).
- The Pi, when plugged into the monitor via converter and DVI cable works, when it's powered from my desktop PC.
- The Pi, when plugged into the monitor via converter and DVI cable does not work, when powered by USB charger. Tried 3 different ones, with output currents 1A, 1.35A and 3A (the last one works with TV, others were not tested).
- My laptop, which happens to have a HDMI output, works with converter and my display.
- The PC does not see the Pi in any way when connected to USB (which does not surprise me, it's for power not communication). Even
I have a thing called 'charger doctor' which is supposed to be USB pass-through with current and voltage meter, alternating them each few seconds on a small display. I do not know if this device offers correct readings and. I haven't cross-verified if the readings are consistent with anything else.
- When the 1A or 1.35A USB charger is connected, it shows something like 5.11-5.14V and 0.19A, with occasional spikes up to 0.24A.
- When the PC is connected, it shows 4.84-4.86V with stable current at 0.20A and spikes up to 0.3A
This is for a device doing nothing but booting Raspbian and than sitting idle.
So, two questions:
- Why it only works when PC is the power source?
- What can I do to make it work with USB power supply?