I don't want to power anything from the HDMI port. My power supply has a neat switch built into the 5v cord, and after shutting down the Pi, I just want to cycle the switch to bring the Pi back alive. However, after shutting it down, (shutdown -h now), the Pi shuts down but the red light stays on. If I momentarily disconnect the HDMI connector, the light goes out. I can plug the HDMI back in and it stays out. Obviously, the HDMI can keep the Pi somewhat alive, but can't power it up again by itself. The HDMI drives a small 7" no-name NTSC/PAL LCD display. Any hints on how to keep the display from back-driving my Pi? Thanks. Tim
To clarify the situation a bit, the red LED is significant, since it means that I can't restart the Pi. Once I shut the Pi down (sudo shutdown now), I wait until I see all of the frantic activity on the 7" display stop and show NO SIGNAL. The computer terminal, since I am running SSH, also shows that the SSH session has been terminated, so I know that the Pi is "dead". I then turn the 5v power off to the Pi (the power supply has a switch in its 5v power cord). The red LED remains on. No matter how long I leave the power off, the LED remains on. If I turn the power switch back on, nothing happens. SSH can't reach the Pi. When I turn the wireless keyboard on (which has a USB dongle plugged into the Pi), it can't make the Pi do anything. Cycling the power switch on and off does nothing. With the power switch off, if I disconnect the HDMI connector, the LED immediately goes off. I plug the power back in (with the switch off) and the LED stays off. I turn the power on and the Pi boots up and is happy.
During most of my usage, the Pi (mod 4B) is connected to the power supply, the 7" display, to an Ethernet switch, and to a USB Wi-Fi dongle that connects it to a keyboard/scratchpad combo, even though I usually leave that turned off. The 7" display only connects to the Pi and to a 5v power supply. Instead of disconnecting the HDMI at the Pi, I can either disconnect it at the display or disconnect the power to the display. Turning the display off has no effect, probably since the "power button" appears to be a capacitive touch switch, so the display is never really turned off.
It really appears that the display back feeds enough power to the Pi to keep the circuitry just alive enough that the powerfail circuitry will not detect that the main 5v power source has been removed and re-applied, but it isn't enough to run anything. It is just enough to screw things up. Tim