Wednesday, December 31, 2014

HDMI-VGA adapter for Raspberry Pi

This year Santa left an HDMI to VGA adapter under the christmas tree. I have an old LCD monitor with only a VGA input while the Raspberry Pi and Beagleboard/Beaglebone boards only have HDMI outputs.
The specific adapter is under $10 from seeedstudio.com, although I see a bunch of others on ebay and other sites that look similar.
Setup on the Raspberry Pi was pretty easy - only one Google search. Had to edit the /boot/config.txt file to force the Pi to use the HDMI output and to set the screen resolution (both VGA and HDMI can report screen resolution back to the host, but it doesn't seem to happen with this setup).
Configuration info was found at www.raspberrypi.org/forums/viewtopic.php?p=269212.
Internally the adapter is just a Chrontel CH7101A chip to do the HDMI-VGA conversion, and an Everest Semiconductor ES7144LV audio output chip. My unit pulls about 180 milliAmps from the +5 volt output of the HDMI connector. That's way more than the 50 mA maximum (according to Wikipedia), but the Pi is driving it without any problems. I haven't tried the adapter with Beagles yet, but research so far indicates that they require an externally powered adapter because they can't supply enough current via HDMI.
Caution: poking around inside will most likely void the warranty and might smoke the adapter and/or the Beagleboard. You're on your own if you try something like this:
Interestingly, there's space on the lower right corner of the PCB for a USB connector as an alternate +5 input. I took out the zero-ohm resistor (R1, just to the left of the USB connector footprint), and brought out 3 wires: Ground, HDMI +5 out, and +5 power in. Now I can just connect the +5's together for the Pi and should be able to use external power for the Beagles.





No comments: