Respectech wrote:I'm trying to use a 7" LCD touchscreen (that I already own) with the RPi2. The LCD is powered through a microUSB cable which also transmits the touchscreen coordinates back through the cable, and has a full-sized HDMI port.
Here's the setup:
* RPi2 with the latest version of Raspbian with all updates
* Desktop Power Supply @ 5.0VDC -> USB to microUSB cable -> RPi2 microUSB port = RPi2 boots up fine
* RPi2 USB port -> USB to microUSB cable -> LCD microUSB port = LCD seems to have a power stability issue
* RPi2 HDMI port -> LCD HDMI port = LCD displays fine when USB power input to LCD is stable (like from an external power supply)
When powering up the RPi2, the LCD turns on and off in a repeating manner. However, if I power it from another USB power supply, the screen works fine and stays powered on properly. This, however, negates the possibility of getting feedback from the touchscreen through the USB port. I tried increasing the voltage on the power supply to 5.25VDC with no improvement. I have not yet tried using a powered USB hub on the RPi2 (I don't have one handy).
The other interesting problem is that the RPi2 seems to only display 640x480 and leaves the right-side 160x480 pixels off. I've tried numerous options in the /boot/config.txt file, but have the same problem.
An interesting thing to note is that the RPi2 seems to be able to downscale resolutions all the way up to 1920x1080 to fit on the LCD. However, at this point it is scaling those resolutions to fit in the leftmost 640 pixels.
Respectech wrote:The next challenge is getting the touchscreen driver to work. I built a USB cable that goes between the Raspberry Pi 2 and the LCD, but has two extra leads (5V and ground) that connect to pins on the 2x20 header. That took care of the power issue.
A compatible driver according to the screen's hardware ID is here: https://github.com/derekhe/waveshare-7i ... een-driver
But I still couldn't get the touchscreen to work after installing that.